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⚛️ Lesson 7 ⚛️ < Back Atomic Structure Lesson 7 ⚛️ Lesson 7 ⚛️ Section Test 1 , Test 2 Previous Next Quiz 1 : Atomic Structure, Isotopes, and Subatomic Particles 1️⃣ Boron is an element in Group 13 of the Periodic Table. a) Define the term "isotope." 🌟 b) Provide the number of i) protons, ii) neutrons, and iii) electrons in one neutral atom of the isotope 11B. 🧪 c) State the relative masses and charges of: i) an electron 🌌 ii) a neutron 🌌 iii) a proton 🌌 2️⃣ Zirconium (Zr) and hafnium (Hf) are metals. a) i) Write the isotopic symbol for the isotope of zirconium with 40 protons and 91 nucleons. 🌟 ii) How many neutrons are present in one atom of this isotope? 🌟 b) Hafnium ions, 18072Hf2+, are produced in a mass spectrometer. How many electrons are present in one of these hafnium ions? 🌟 c) Describe the behavior of a beam of protons passing through the gap between charged plates and explain what happens when a beam of neutrons passes through the same gap. 🌌 3️⃣ a) Describe the structure of an atom, including details of the subatomic particles present. 🌟 b) Explain the terms atomic number and nucleon number. 🌌 c) Copy and complete the table: Neutral atom | Atomic number | Nucleon number | Numbers of each subatomic particle present Mg | 12 | 24 | Al | 13 | 27 | d) Explain why atoms are neutral. 🌌 e) Explain why an oxygen atom cannot have 9 protons. 🌌 f) Explain why electrons are not used when calculating the relative mass of an atom. 🌌 4️⃣ The symbols below describe two isotopes of the element uranium. 235 92U 238 92U a) Define the term "isotope." 🌟 b) i) In what ways are these two isotopes of uranium identical? 🌟 ii) In what ways do they differ? 🌟 c) State the number of electrons present in one U2+ ion. 🌌 5️⃣ The table below shows the two naturally occurring isotopes of chlorine. a) Copy and complete the table: 35 17Cl 37 17Cl number of protons | number of electrons | number of neutrons | b) Based on the relative atomic mass of chlorine (35.5), what can you infer about the relative abundance of the two naturally occurring isotopes of chlorine? 🌟 c) i) Explain why a magnesium ion is positively charged. 🌌 ii) Explain why a chloride ion has a single negative charge. 🌌 Note: 🌟 indicates questions with fill-in-the-blank format, and 🌌 indicates multiple-choice questions. Good luck! 🧪🔬 Answers 1️⃣ Boron is an element in Group 13 of the Periodic Table. a) The term "isotope" refers to different forms of an element that have the same number of protons but different numbers of neutrons. b) i) Protons: 5, ii) Neutrons: 6, iii) Electrons: 5. 2️⃣ Zirconium (Zr) and hafnium (Hf) are metals. a) i) The isotopic symbol for the isotope of zirconium with 40 protons and 91 nucleons is 9123Zr. ii) The number of neutrons in one atom of this isotope is 51. b) The hafnium ion (18072Hf2+) contains 68 electrons. c) - i) The beam of protons passing through the gap between the charged plates is deflected towards the negative plate due to the electric field. ii) When a beam of neutrons passes through the gap between the charged plates, it remains unaffected as neutrons are neutral particles. 3️⃣ a) The structure of an atom consists of subatomic particles: protons and neutrons located in the nucleus, and electrons orbiting the nucleus. b) - Atomic number represents the number of protons in an atom's nucleus. Nucleon number (mass number) represents the total number of protons and neutrons in an atom's nucleus. c) Neutral atom | Atomic number | Nucleon number | Numbers of each subatomic particle present Mg | 12 | 24 | 12 protons, 12 neutrons, 12 electrons Al | 13 | 27 | 13 protons, 14 neutrons, 13 electrons d) Atoms are neutral because they have an equal number of protons and electrons, resulting in a net charge of zero. e) An oxygen atom cannot have 9 protons because the number of protons determines the element's identity, and oxygen is defined by having 8 protons. f) Electrons are not used when calculating the relative mass of an atom because their mass is significantly smaller compared to protons and neutrons. Their contribution to the total mass is negligible. 4️⃣ The symbols below describe two isotopes of the element uranium. 235 92U 238 92U a) The term "isotope" refers to different forms of an element that have the same number of protons but different numbers of neutrons. b) - i) These two isotopes of uranium are identical in terms of the number of protons (92) and the chemical properties. ii) They differ in terms of their mass number (235 and 238) and the number of neutrons. c) One U2+ ion has 90 electrons. 5️⃣ The table below shows the two naturally occurring isotopes of chlorine. a) 35 17Cl 37 17Cl number of protons | 17 | 17 number of electrons | 17 | 17 number of neutrons | 18 | 20 b) The relative atomic mass of 35.5 suggests that the two isotopes of chlorine have approximately equal abundance. c) - i) A magnesium ion is positively charged because it has lost two electrons, resulting in more protons than electrons. ii) A chloride ion has a single negative charge because it has gained one electron, resulting in more electrons than protons. Well done on completing the quiz! Keep up the great work! 🔬🎉 Quiz 2 : Atomic Structure, Isotopes, and Subatomic Particles 1️⃣ Boron is an element in Group 13 of the Periodic Table. a) Boron has two isotopes. 🔄❓ What do you understand by the term isotope ? [1] b) State the number of: i) protons, ii) neutrons, and iii) electrons in one neutral atom of the isotope 11 5B. [3] c) State the relative masses and charges of: i) an electron, ii) a neutron, and iii) a proton. [2] 2️⃣ Zirconium, Zr, and hafnium, Hf, are metals. An isotope of zirconium has 40 protons and 91 nucleons. ⚛️❓ a) i) Write the isotopic symbol for this isotope of zirconium. [1] ii) How many neutrons are present in one atom of this isotope? [1] b) Hafnium ions, 18072Hf2+ , are produced in a mass spectrometer. How many electrons are present in one of these hafnium ions? [1] c) The subatomic particles present in zirconium and hafnium are electrons, neutrons, and protons. A beam of protons is fired into an electric field produced by two charged plates, as shown in the diagram below: ) Describe how the beam of protons behaves when it passes through the gap between the charged plates. Explain your answer. [2] ii) Describe and explain what happens when a beam of neutrons passes through the gap between the charged plates. [2] 3️⃣ a) Describe the structure of an atom, giving details of the subatomic particles present. 🏢🔬 [6] b) Explain the terms: Atomic number, and Nucleon number. [2] c) Copy and complete the table: d) Explain why atoms are neutral. [1] e) An oxygen atom has 8 protons in its nucleus. Explain why it cannot have 9 protons. [1] f) When calculating the relative mass of an atom, the electrons are not used in the calculation. Explain why not. [1] 4️⃣ The symbols below describe two isotopes of the element uranium. 235 92U 238 92 U a) State the meaning of the term isotope . [1] b) i) In what ways are these two isotopes of uranium identical? [2] ii) In what ways do they differ? [2] c) In a mass spectrometer, uranium atoms can be converted to uranium ions, U2+ . State the number of electrons present in one U2+ ion. [1] 5️⃣ The table below shows the two naturally occurring isotopes of chlorine. a) Copy and complete the table: b) The relative atomic mass of chlorine is 35.5. What does this tell you about the relative abundance of the two naturally occurring isotopes of chlorine? [2] c) Magnesium chloride contains magnesium ions, Mg2+ , and chloride ions, Cl– . i) Explain why a magnesium ion is positively charged. [1] ii) Explain why a chloride ion has a single negative charge. [2] Total = 50 🌟 ✨ Quiz Answers: ✨ 1a) Isotope refers to different forms of an element with the same number of protons but different numbers of neutrons. 1b) i) Protons: 5, ii) Neutrons: 6, iii) Electrons: 5 1c) i) Electron: Relative mass = 1/1837 amu, Charge = -1 e ii) Neutron: Relative mass = 1 amu, Charge = 0 iii) Proton: Relative mass = 1 amu, Charge = +1 e 2a) i) 91Zr ii) Neutrons: 51 2b) Electrons: 72 2c) i) The beam of protons is deflected towards the negatively charged plate due to their positive charge. ii) Neutrons are electrically neutral, so they are not affected by the electric field and continue on a straight path. 3a) An atom consists of a nucleus (containing protons and neutrons) surrounded by electrons in energy levels or shells. 3b) - Atomic number: Number of protons in an atom's nucleus. - Nucleon number: Total number of protons and neutrons in an atom's nucleus. 3c) e) The number of protons determines the identity of an element. Changing the number of protons would result in a different element. f) Relative mass calculations focus on the mass of the nucleus, which is primarily determined by protons and neutrons. Electrons contribute negligible mass. 4a) Isotope refers to different forms of an element with the same number of protons but different numbers of neutrons. 4b) i) Both isotopes have the same number of protons (92) and belong to the element uranium. ii) They differ in the number of neutrons: Uranium-235 has 143 neutrons, while uranium-238 has 146 neutrons. 4c) U2+ ion has 90 electrons. 5a) | | 35 | 17 Cl | 37 | 17 b) The relative atomic mass of 35.5 indicates that there is a mixture of the two isotopes of chlorine, with a higher abundance of the isotope with a mass number of 35.c) i) A magnesium ion is positively charged because it has lost two electrons, resulting in a net positive charge. ii) A chloride ion has a single negative charge because it has gained one electron, resulting in a net negative charge.I hope you enjoyed the quiz! 🎉

d46c3f20-3f31-4e9f-8deb-0dbd0d3b1ee2 Atomicity explanation General Lesson: Atomicity 🔬 Introduction: In chemistry, atomicity refers to the number of atoms present in a molecule. It tells us how many atoms of an element are bonded together to form a single unit of a compound. Understanding atomicity is crucial in determining the properties and behavior of substances at the atomic level. Let's explore the concept of atomicity in more detail. 💡 Definition of Atomicity: Atomicity is the term used to describe the number of atoms bonded together within a molecule. It represents the smallest unit of a compound that retains the chemical properties of that substance. 🔍 Examples of Atomicity: Oxygen (O2): Oxygen gas consists of two oxygen atoms bonded together. This means the atomicity of oxygen gas is 2, indicating that two oxygen atoms are chemically bonded within each oxygen molecule. Ozone (O3): Ozone is a molecule composed of three oxygen atoms bonded together. The atomicity of ozone is 3, signifying that three oxygen atoms form each ozone molecule. Hydrogen (H2): Hydrogen gas consists of two hydrogen atoms bonded together, giving it an atomicity of 2. 🔬 Determining Atomicity: To determine the atomicity of a molecule, we examine its chemical formula and identify the number of atoms of each element present. The subscript numbers in the formula represent the atomicity. 💥 Significance of Atomicity: Atomicity plays a significant role in understanding the physical and chemical properties of substances. It influences factors such as reactivity, stability, and bonding behavior. 🧪 Quiz (Basic Understanding): What does atomicity refer to? a) The number of atoms bonded together within a molecule. b) The mass of an atom. c) The atomic number of an element. What is the atomicity of oxygen gas (O2)? a) 1 b) 2 c) 3 How many atoms are bonded together in a water molecule (H2O)? a) 1 b) 2 c) 3 What does the atomicity of a compound determine? a) Its color b) Its physical state c) The number of atoms in a molecule What is the atomicity of hydrogen gas (H2)? a) 1 b) 2 c) 3 🔍 Answers: a) The number of atoms bonded together within a molecule. b) 2 b) 2 c) The number of atoms in a molecule b) 2 Great job! You've gained a basic understanding of atomicity and its significance in chemistry. Keep exploring the world of atoms and molecules to deepen your knowledge in this exciting field!

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4d273e93-9c73-4a5f-a142-6b5097399467 Boyle's Law The principle that states the volume of a given amount of gas is inversely proportional to its pressure at a constant temperature.

3bf487dc-3f9b-45fc-8132-84460b422a56 < Back Previous Next Time, temperature, mass & volume Time Time can be measured using a stopwatch or stopclock which are usually accurate to one or two decimal places The units of time normally used are seconds or minutes Other units may be used for extremely slow reactions (e.g. rusting) Remember: 1 minute = 60 seconds Examiner Tips and Tricks Careful: Units of time often cause issues in results tables. If the display on a stopwatch showed 1:30. The incorrect time to record would be 1.30 minutes. The correct time would be 1.5 minutes. To avoid any confusion, if the time intervals are less than a minute, it is best / easire to change the recorded units to seconds. So, the same stopwatch display would be recorded as 90 seconds. Temperature Temperature is measured with a thermometer or digital temperature probe Laboratory thermometers usually have a precision of a half or one degree Digital temperature probes are available which are more precise than traditional thermometers and can often read to 0.1 oC Traditional thermometers rely upon the uniform expansion and contraction of a liquid substance with temperature Digital temperature probes can be just as, if not, more accurate than traditional thermometers The units of temperature are degrees Celsius (ºC) Mass Mass is measured using a digital balance which normally gives readings to two decimal places Balances should be tared (set to zero) before use Balances should also be allowed time to settle on a final measurement / reading before it is recorded The standard unit of mass in kilograms (kg) However, in chemistry grams (g) are most often used Remember: 1 kilogram = 1000 grams Volumes of liquid The volume of a liquid can be determined using different pieces of apparatus The choice of apparatus depends on the level of accuracy needed Three common pieces of apparatus for measuring the volume of a liquid are: Burettes Volumetric pipettes Measuring cylinders Burettes are the most accurate way of measuring a variable volume of liquid between 0 cm3 and 50 cm3 They are most commonly used in titrations Careful: Read the burette scale from top to bottom as 0.00 cm3 is at the top of the column Volumetric pipettes are the most accurate way of measuring a fixed volume of liquid, They have a scratch mark on the neck which is matched to the bottom of the meniscus to make the measurement A pipette filler is used to draw the liquid into the volumetric pipette The most common volumes for volumetric pipettes are 10 cm3 and 25 cm3 Measuring cylinders are used when approximate volumes are required (accuracy is not an important factor) These are graduated (have a scale so can be used to measure) Measuring cylinders typically range from 10 cm3 to 1 litre (1 dm3) Whichever apparatus you use, you may see markings in millilitres, ml, which are the same as a cm3 Volumes of gas For some experiments, the volume of a gas produced needs to be measured This is typically done by using one of the following methods: Using a gas syringe By downward displacement of water A gas syringe is more precise and accurate than downward displacement of water Diagram of the set-up for an experiment involving a gas syringe Downward displacement of water is where a measuring cylinder is inverted in water to collect the gas produced This method does not work if the gas is soluble in water Diagram of the set-up for an experiment collecting gas by downward displacement of water If the gas happens to be heavier than air and is coloured, the cylinder does not need to be inverted Advantages & disadvantages of methods & apparatus In the lab, we often have choices of different apparatus to do the same job Evaluating which piece of apparatus is the best one to use is part of good experimental planning and design This means appreciating some of the advantages and disadvantages of laboratory apparatus Advantages and disadvantages of lab apparatus Apparatus Advantage Disadvantage Temperature probe More precise readings Easy to make multiple repeat readings Can be automated to run over long periods of time Can be corroded by some reagents More expensive (to replace) Volumetric pipette Accurate measurement of a fixed volume Harder to use than a normal pipette Only measures one fixed volume Gas syringe Easy to set up Keeps the gas dry The syringe can stick Collects limited volumes Expensive and delicate / fragile Microscale experiments Less wasteful Saves energy Safer Hard to see what's happening Lose a lot of material separating / purifying the products Five pieces of apparatus that can be used to measure the volume of a liquid. They all have their pros and cons Planning your method Good experimental design includes the answers to questions like Have I chosen a suitable apparatus for what I need to measure? Is it going to give me results in an appropriate time frame? Is it going to give me enough results to process, analyse and make conclusions? Does it allow for repetitions to check how reliable my results are? Does my plan give a suitable range of results? How can I be sure my results are accurate ? Have I chosen an appropriate scale of quantities without being wasteful or unsafe? You may be asked about experimental methods in exam questions and your experience and knowledge of practical techniques in chemistry should help you to spot mistakes and suggest improvements Solutions You need to know all the following terms used when describing solutions: Terminology about solutions table Term Meaning Example Solvent The liquid in which a solute dissolves The water in seawater Solute The substance which dissolves in a liquid to form a solution The salt in seawater Solution The mixture formed when a solute is dissolved in a solvent Seawater Saturated solution A solution with the maximum concentration of solute dissolved in the solvent Seawater in the Dead Sea Soluble A substance that will dissolve Salt is soluble in water Insoluble A substance that will not dissolve Sand is insoluble in water Filtrate The liquid or solution that has passed through a filter Fresh coffee in a cup Residue The substance that remains after evaporation, distillation, filtration or any other similar process Coffee grounds in filter paper Acid-base titrations Titrations are a method of analysing the concentration of solutions They can determine exactly how much alkali is needed to neutralise a quantity of acid – and vice versa You may be asked to perform titration calculations to determine the moles present in a given amount or the concentration / volume required to neutralise an acid or a base Titrations can also be used to prepare salts Apparatus 25 cm3 volumetric pipette Pipette filler 50 cm3 burette 250 cm3 conical flask Small funnel 0.1 mol / dm3 sodium hydroxide solution Sulfuric acid of unknown concentration A suitable indicator Clamp stand, clamp & white tile The steps in performing a titration Method Use the pipette and pipette filler and place exactly 25 cm3 sodium hydroxide solution into the conical flask Using the funnel, fill the burette with hydrochloric acid placing an empty beaker underneath the tap. Run a small portion of acid through the burette to remove any air bubbles Record the starting point on the burette to the nearest 0.05 cm3 Place the conical flask on a white tile so the tip of the burette is inside the flask Add a few drops of a suitable indicator to the solution in the conical flask Perform a rough titration by taking the burette reading and running in the solution in 1 – 3 cm3 portions, while swirling the flask vigorously Quickly close the tap when the end-point is reached The endpoint is when one drop causes a sharp colour change Record the volume of hydrochloric acid added, in a suitable results table as shown below Make sure your eye is level with the meniscus Repeat the titration with a fresh batch of sodium hydroxide As the rough end-point volume is approached, add the solution from the burette one drop at a time until the indicator just changes colour Record the volume to the nearest 0.05 cm3 Repeat until you achieve two concordant results (two results that are within 0.1 cm3 of each other) to increase accuracy Rough titre Titre 1 Titre 2 Titre 3 Final reading (cm3) First reading (cm3) Titre (cm3) Examiner Tips and Tricks Common errors during a titration include: Not removing the funnel from the burette This can lead to some liquid dripping into the burette and cause false / high readings Not filling the jet space of the burette The jet space is the part of the burette after the tap Not filling this space can lead to false readings Reading the volume from the burette incorrectly Readings should be taken from the bottom of the meniscus Careful: The scale on the burette has 0.0 cm3 at the top and 50 cm3 (typically) at the bottom Indicators Indicators are used to show the endpoint in a titration Wide range indicators such as litmus are not suitable for titration as they do not give a sharp colour change at the endpoint However, methyl orange and phenolphthalein are very suitable Some of the most common indicators with their corresponding colours are shown below: Common acid-base indicators Indicator Colour in acid Colour in alkali Colour in neutral Litmus solution Red Blue Purple Red litmus paper Stays red Turns blue No change Blue litmus paper Turns red Stays blue No change Methyl orange Red Yellow Orange Phenolphthalein Colourless Pink Colourless Thymolphthalein Colourless Blue Colourless Paper chromatography Chromatography is used to separate substances and provide information to help identify them The components have different solubilities in a given solvent E.g. Different coloured inks that have been mixed to make black ink A pencil line is drawn on chromatography paper and spots of the sample are placed on it A pencil is used for this as ink would run into the chromatogram along with the samples The paper is then lowered into the solvent container, making sure that the pencil line sits above the level of the solvent so the samples don’t wash into the solvent container The solvent used is usually water but it can be other substances such as ethanol The solvent travels up the paper by capillary action , taking some of the coloured substances with it Different substances have different solubilities so they will travel at different rates, causing the substances to spread apart Those substances with higher solubility will travel further than the others How to carry out chromatography The pigments in ink can be analysed using paper chromatography Interpret simple chromatograms We can use a chromatogram to compare the substances present in a mixture to known substances and make assumptions Pure substances will produce only one spot on the chromatogram Impure substances will produce more than one spot on the chromatogram If two or more substances are the same, they will produce identical chromatograms If the substance is a mixture , it will separate on the paper to show all the different components as separate spots It is common practice to include a known compound as a reference spot This can help match up to an unknown spot or set of spots in order to identify it Example chromatogram results The brown ink has separated showing a spot of red ink, blue ink and yellow ink We can draw several conclusions from this chromatogram: The brown ink is a mixture as there are three dots Red, yellow and blue are pure as there is only one dot for each The brown ink contains red, blue and yellow as the dots are in line with one another horizontally Examiner Tips and Tricks Chromatograms in exams will be in black and white so to identify whether a mixture contains a known sample, the dots need to be in line with one another. Locating agents Extended tier only For chromatography to be useful, the chemist needs to be able to see the components move up the paper This is not the case for colourless substances such as amino acids or sugars Locating agents can be used to see the spots These are substances which react with the sample and produce a visible / coloured spot for the product(s) The chromatogram is treated with the agent after the chromatography run has been carried out, making the sample runs visible to the naked eye Retention factor (Rf) values Extended tier only R f values are used to identify the components of mixtures The R f value of a particular compound is always the same However, it does depend on the solvent used If the solvent is changed then the R f value changes Calculating the R f value allows chemists to identify unknown substances because it can be compared with the R f values of known substances under the same conditions The retention factor, R f, is calculated by the equation: R f = The R f value: Is a ratio Has no units Will always be less than 1 Worked Example A student obtained the following chromatogram when carrying out chromatography. Calculate the R f value of the substance. Answer: The R f value of the substances in the chromatogram above can be calculated by: R f = = = 0.5 Examiner Tips and Tricks When you calculate R f values in exams, make sure to use your ruler carefully to measure the distance moved by the solvent and the substance as mark schemes can be strict about the values accepted for these. Filtration & crystallisation The choice of separation technique depends on the substances being separated All techniques rely on a difference in properties of the chemicals in the mixture This is usually a physical property such as boiling point Separating a mixture of solids Differences in solubility can be used to separate solids For a difference in solubility, a suitable solvent must be carefully chosen Only the desired substance should dissolve in the solvent Other substances or impurities in the mixture should not dissolve in the solvent For example, to separate a mixture of sand and salt: Water is a suitable solvent because salt is soluble in water, but sand is insoluble in water Filtration This technique is used to separate an undissolved solid from a mixture of the solid and a liquid / solution ( e.g. sand from a mixture of sand and water) Centrifugation can also be used for this mixture A filter paper is placed in a filter funnel above another beaker The mixture of insoluble solid and liquid is poured into the filter funnel The filter paper will only allow small liquid particles to pass through in the filtrate Solid particles are too large to pass through the filter paper so will stay behind as a residue Filtration of a mixture of sand and water Crystallisation This method is used to separate a dissolved solid from a solution A simple application of this is to heat a solution to boiling, remove the heat and leave the solvent to evaporate A more common application of this is sometimes called crystallisation This is when the solid is more soluble in hot solvent than in cold, e.g. copper sulphate from a solution of copper(II) sulphate The solution is heated, allowing the solvent to evaporate and leaving a saturated solution behind You can test if the solution is saturated by dipping a clean, dry, cold glass rod into the solution If the solution is saturated, crystals will form on the glass rod when it is removed and allowed to cool The saturated solution is allowed to cool slowly Solids will come out of the solution as the solubility decreases This will be seen as crystals growing The crystals are collected by filtration They are then washed with distilled water to remove any impurities Finally, they are allowed to dry Common places to dry crystals are between sheets of filter paper or in a drying oven The process of crystallisation The solution is slowly heated to remove around half of the liquid. The remaining liquid will evaporate slowly Examiner Tips and Tricks In exams, you need to be specific that no more than half of the solution is removed by direct heating or you may lose a mark. Distillation: simple & fractional Simple distillation Distillation is used to separate a liquid and soluble solid from a solution (e.g. water from a solution of saltwater) or a pure liquid from a mixture of liquids The solution is heated and pure water evaporates producing a vapour which rises through the neck of the round-bottomed flask The vapour passes through the condenser , where it cools and condenses, turning into pure water which is collected in a beaker After all the water is evaporated from the solution, only the solid solute will be left behind Simple distillation apparatus Diagram showing the distillation of a mixture of salt and water Simple distillation can be used to separate the products of fermentation, such as alcohol and water However, fractional distillation is a more effective separation technique, commonly used when the boiling points of the liquids are close and/or a higher degree of purity is required, such as crude oil Fractional distillation Used to separate two or more liquids that are miscible with one another (e.g. ethanol and water from a mixture of the two) The solution is heated to the temperature of the substance with the lowest boiling point This substance will rise and evaporate first The vapours will pass through a condenser, where they cool and condense The condensed liquid is then collected in a beaker All of the substance is evaporated and collected, leaving behind the other component(s) of the mixture For water and ethanol: Ethanol has a boiling point of 78 ºC Water has a boiling point of of 100 ºC The mixture is heated until it reaches 78 ºC, at which point the ethanol distills out of the mixture and into the beaker When the temperature starts to increase to 100 ºC heating should be stopped as the water and ethanol are now separated Fractional distillation of a mixture of ethanol and water An electric heater is safer to use when there are flammable liquids present The separation of the components in petroleum is achieved by fractional distillation on an industrial scale Fractional distillation of crude oil is not carried out in school laboratories due to the toxic nature of some of the components of the crude oil, but it can sometimes be simulated using a synthetic crude oil made specially for the demonstration Worked Example A student is given a mixture of calcium sulfate, magnesium chloride and water. The table below shows some information about calcium sulfate and magnesium chloride. substance solubility in water state at room temperature calcium sulfate insoluble solid magnesium chloride soluble solid How does the student obtain magnesium chloride crystals from the mixture? Crystallisation followed by distillation Crystallisation followed by filtration Distillation followed by crystallisation Filtration followed by crystallisation Answer The correct answer is D because: The difference in solubility in water means the first step is to make a solution The magnesium chloride will dissolve, but the solid calcium sulfate will be left behind The mixture is filtered to remove the calcium sulfate and then evaporated and crystallised to obtain magnesium chloride crystals Examiner Tips and Tricks You may be asked how to separate a mixture of gases: One method involves cooling the gaseous mixture sufficiently to liquefy all of the gases, which are then separated by fractional distillation. They can also be separated by diffusion, where the boiling points are very close or it is impractical or expensive to use fractional distillation. Assessing purity Pure substances melt and boil at specific and sharp temperatures For example, water has a boiling point of 100°C and a melting point of 0°C Mixtures have a range of melting and boiling points as they consist of different substances that melt or boil at different temperatures Therefore, melting and boiling point data can be used to distinguish pure substances from mixtures An unknown pure substance can be identified by experimentally determining its melting point and boiling point and comparing them to literature values / data tables Boiling points are commonly determined by distillation Melting point analysis is routinely used to assess the purity of drugs for example This is done using a melting point apparatus which allows you to slowly heat up a small amount of the sample, making it easier to observe the exact melting point Melting point test using an oil bath This is then compared to data tables The closer the measured value is to the actual melting or boiling point, the purer the sample is If the sample contains impurities: The boiling point may appear higher than the sample's actual boiling point The melting point may appear lower than the sample's actual melting point Identification of anions Negatively charged non-metal ions are known as anions You must be able to describe the tests for the following ions: Carbonate ions, CO32– Halide ions, Cl– , Br– , I– Nitrate ions, NO3– Sulfate ions, SO42– Sulfite ions, SO32– Test for carbonate ions Carbonate compounds contain the carbonate ion, CO32- The test for the carbonate ion is: Add dilute acid Bubble the gas released through limewater Limewater turns cloudy if the carbonate ion is present If a carbonate compound is present then fizzing / effervescence should be seen as CO2 gas is produced, which forms a white precipitate of calcium carbonate when bubbled through limewater: CO32- (aq) + 2H+ (aq) → CO2 (g) + H2O (l) CO2 (g) + Ca(OH)2 (aq) → CaCO3(s) + H2O(l) The white precipitate turns limewater cloudy Testing for carbonate ions Limewater turns milky in the presence of carbon dixoide caused by the formation of insoluble calcium carbonate Examiner Tips and Tricks If you are asked to describe the test for carbonate ions, make sure that you say: Bubble the gas produced through limewater, which turns cloudy if the carbonate ion is present Just saying that limewater turns cloudy is not enough This isn't describing the test, it is stating the result Test for halide ions Halide ions are the negative ions / anions formed by the elements in Group 7 The test for the halide ions is: Acidify the sample with nitric acid Add silver nitrate solution, AgNO3, A silver halide precipitate forms if a halide ion is present The precipitate is indicated by the state symbol (s) The colour of the silver halide precipitate depends on the halide ion: The chloride ion forms a white precipitate of silver chloride potassium chloride + silver nitrate → potassium nitrate + silver chloride KCl (aq) + AgNO3 (aq) → KNO3 (aq) + AgCl (s) The bromide ion forms a cream precipitate of silver bromide potassium bromide + silver nitrate → potassium nitrate + silver bromide KBr (aq) + AgNO3 (aq) → KNO3 (aq) + AgBr (s) The iodide ions forms a yellow precipitate of silver iodide potassium iodide + silver nitrate → potassium nitrate + silver iodide KI (aq) + AgNO3 (aq) → KNO3 (aq) + AgI (s) Testing for halide ions Each silver halide produces a precipitate of a different colour Examiner Tips and Tricks The acidification step in the halide ion test must be done with nitric acid rather than hydrochloric acid. HCl contains the chloride ion which would interfere with the results. Test for nitrate ions Nitrate compounds contain the nitrate ion, NO3– The test for the nitrate ion is Add aqueous NaOH and aluminium foil Warm gently and test the gas released The gas given off is ammonia, NH3 Ammonia is a gas with a characteristic sharp choking smell that turns damp red litmus paper blue Test for sulfate ions Sulfate compounds contain the sulfate ion, SO42- The test for the sulfate ion is: Acidify the sample with dilute nitric acid Add a few drops of barium nitrate solution A white precipitate of barium sulfate is formed, if the sulfate ion is present Ba2+ (aq) + SO42- (aq) → BaSO4 (s) The test can also be carried out with barium nitrate solution Testing for sulfate ions A white precipitate of barium sulfate is a positive result for the presence of sulfate ions Examiner Tips and Tricks Nitric is added first to remove any carbonates which may be present which would also produce a precipitate and interfere with the results. Test for sulfite ions Sulfite compounds contain the sulfite ion, SO32- The test for the sulfite ion is: Add dilute acid Warm the mixture gently Bubble the gas released through potassium manganate(VII) solution The potassium manganate(VII) solution changes from purple to colourless if the sulfite ion is present Examiner Tips and Tricks For qualitative inorganic analysis, there will be one test for the metal cation and another test for the non-metal anion . If you are an extended level student you may be asked to write balanced ionic equations for cation and anions tests, so make sure you know the formulae of all the ions and precipitates formed. Identification of cations Test for ammonium ions Ammonium ions, NH4+, can be identified by gently warming a solution containing the ions with sodium hydroxide solution The sodium hydroxide solution is a source of hydroxide ions, OH–, for the test This releases ammonia gas which turns damp red litmus paper blue Testing for ammonium ions Heating ammonium ions with sodium hydroxide solution releases ammonia gas which turns damp red litmus blue Metal cations in aqueous solution can be identified by the colour of the precipitate they form on addition of sodium hydroxide and ammonia Most transition metals produce hydroxides with distinctive colours Test for metal ions with sodium hydroxide solution If a small amount of sodium hydroxide solution is used, the resulting metal hydroxide normally precipitates out of solution If excess sodium hydroxide solutionis used, some of the precipitates may re-dissolve For this reason, just a few drops of sodium hydroxide solutionare added at first and very slowly The sodium hydroxide test for the metal ion is: Add a few drops of sodium hydroxide solution Record any colour changes or precipitates formed Add excess sodium hydroxide solution Record any colour changes or changes to precipitates Test for metal ions with ammonia solution If a small amount of ammonia solution is used, the resulting metal hydroxide normally precipitates out of solution If excess ammonia solution is used, some of the precipitates may re-dissolve For this reason, just a few drops of ammonia solution are added at first and very slowly The ammonia test for the metal ion is: Add a few drops of ammonia solution Record any colour changes or precipitates formed Add excess ammonia solution Record any colour changes or changes to precipitates Metal ion tests summary Initially, sodium hydroxide solution and ammonia solution give the same results for 2 - 3 drops This is because they both contain the hydroxide ion, OH– Metal Ion Addition of 2-3 drops of NaOH or ammonia Addition of excess NaOH Addition of excess ammonia Al3+ White precipitate forms Precipitate dissolves to form a colourless solution Precipitate does not dissolve Ca2+ White precipitate forms Precipitate does not dissolve Precipitate does not dissolve Cr3+ Green precipitate forms Precipitate dissolves to form a green solution Precipitate does not dissolve Cu2+ Light blue precipitate forms Precipitate does not dissolve Precipitate dissolves to form a dark blue solution Fe2+ Green precipitate forms Precipitate does not dissolve Precipitate does not dissolve Fe3+ Brown precipitate forms Precipitate does not dissolve Precipitate does not dissolve Zn2+ White precipitate forms Precipitate dissolves to form a colourless solution Precipitate dissolves to form a colourless solution Analysing results The tables above contain the results for all metal cations included in the syllabus If a precipitate is formed from either sodium hydroxide or ammonia solution, then the hydroxide is insoluble in water For example, zinc chloride: ZnCl2 (aq) + 2NaOH (aq) → Zn(OH)2 (s) + 2NaCl (aq) There are 3 metal ions that all form white precipitates: Aluminium ions, Al3+ Calcium ions, Ca2+ Zinc ions, Zn2+ Calcium ions, Ca2+, can be easily distinguished from Zn2+ and Al3+ The white precipitate of calcium hydroxide does not dissolve in excess sodium hydroxide solution The white precipitates of zinc hydroxide and aluminium hydroxide dissolve in excess sodium hydroxide solution Zinc ions, Zn2+, can then be distinguished from Al3+ ions as The white precipitate of zinc hydroxide dissolves in excess ammonia solution The white precipitate of aluminium hydroxide does not dissolve in excess ammonia solution Examiner Tips and Tricks The ammonia or sodium hydroxide solution must be added very slowly. If it is added too quickly and the precipitate is soluble in excess, then you run the risk of missing the formation of the initial precipitate, which dissolves as quickly as it forms if excess solution is added. Be sure to distinguish between the term “ colourless ” and “ clear ”. A solution that loses its colour has become colourless. A clear solution is one that you can see through such as water. Solutions can be clear and have colour eg. dilute copper sulphate. Flame tests for metal ions The flame test is used to identify the metal cations by the colour of the flame they produce Ions from different metals produce different colours Dip the loop of an unreactive metal wire such as nichrome or platinum in concentrated acid and then hold it in the blue flame of a Bunsen burner until there is no colour change This is an important step as the test will only work if there is just one type of ion present Two or more ions means the colours will mix, making identification erroneous This cleans the wire loop and avoids contamination A small sample of the compound is placed on an unreactive metal wire loop such as nichrome or platinum Dip the loop into the solid sample / solution and place it in the edge of the blue Bunsen flame Avoid letting the wire get so hot that it glows red otherwise this can be confused with a flame colour Diagram showing the technique for carrying out a flame test The colour of the flame is observed and used to identify the metal ion present: Cation Flame Colour Li+ Crimson Na+ Yellow K+ Lilac Ca2+ Red Ba2+ Apple-green Cu2+ Blue-green Metal ions form distinctive coloured flames Experimental Techniques Next Topic

⚛️ Lesson 1 ⚛️ < Back Atomic Structure Lesson 1 ⚛️ Lesson 1 ⚛️ Get Ready by joining Lesson 1 , it is easy but you need to know it .Explore the structure of an atom and its subatomic particles in this visually enhanced quiz. Learn about atomic and ionic radii, understand the role of protons, neutrons, and electrons, and discover how to determine the number of neutrons in an atom. Embark on a journey through the microcosm of atoms and ions and unlock the secrets of the periodic table! Previous Next ⚛️ 1.1.1Structure of an Atom ⚛️ Welcome ! Today we are diving into the heart of matter to understand the structure of an atom. Let's get started! 💠 Atomic Structure 💠 Matter, as we know it, is composed of atoms, the smallest particles of an element capable of engaging in chemical reactions. The core of an atom is a very small, dense nucleus surrounded by a large area of mostly empty space. 1️⃣ Nucleus: It contains protons and neutrons, giving the nucleus an overall positive charge. 2️⃣ Protons: These particles carry a positive charge. 3️⃣ Neutrons: These particles are neutral, with no charge. 4️⃣ Electrons: These are negatively charged particles that reside in orbitals around the nucleus. Remember, the diagram of an atom is not to scale; the nucleus is much smaller compared to the overall size of the atom. 🎲 Subatomic Particles 🎲 Atoms are made up of protons, neutrons, and electrons, referred to as subatomic particles. Their masses and charges are usually relative and not actual charges and masses. 1️⃣ Protons and Neutrons: They both have a similar mass and are assigned a relative mass of 1. 2️⃣ Electrons: They are 1836 times smaller than a proton or a neutron, and their mass is usually considered negligible. Here are their relative masses and charges: Proton: Relative mass = 1, Charge = +1 Neutron: Relative mass = 1, Charge = 0 Electron: Relative mass ≈ 0 (negligible), Charge = -1 Q1: What are the relative masses and charges of protons, neutrons, and electrons? 🐘🪶 Picture this: a colossal elephant 🐘 named Proton, a mighty rhino 🦏 named Neutron, and a tiny, agile mouse 🐁 called Electron. These three are the heart and soul of our extraordinary, molecular circus, much like protons, neutrons, and electrons being the star ⭐ performers in the grand show of an atom. Just like in a regular circus, it's important to know our performers' talents and traits. But we can't use the conventional tools 🔧🔨! Imagine trying to weigh these performers on a feather 🪶 scale. It's just not accurate enough! It's the same with subatomic particles: we can't measure their masses and charges using everyday units like grams or coulombs. So, to bypass this problem, we dive into the world of 'relatives' 🎭. Imagine if we said, "Compared to the elephant 🐘, the rhino 🦏 weighs the same, but the mouse 🐁 is much, much lighter." We're not giving their weights in pounds or kilograms; instead, we're comparing their weights relative to each other. In the same manner, the mass of a proton is taken as a standard 🏆 (like our elephant 🐘), and it's given a 'relative mass' of 1️⃣. The neutron (our rhino 🦏) also weighs as much as the proton, so it too has a relative mass of 1️⃣. But our tiny mouse 🐁, the electron, is much lighter, with a relative mass of only 1/1836 ❗ And just like our performers have different weights, they also have different charges. The proton (our jolly, positive 🟢 elephant) has a relative charge of +1️⃣, the electron (the negatively charged 🔴 mouse) has -1️⃣, and the neutron (the neutral 🔘 rhino) is a 0️⃣. So remember, these 'relative' masses and charges are like comparisons, not actual masses or charges. It's like comparing our elephant, rhino, and mouse in our molecular circus! 🎪🌈 🔑 Atomic Key Terms 🔑 There are a few terms that you need to know to understand the structure of an atom. 1️⃣ Atomic Number (Z): It is the number of protons in the nucleus of an atom. In a neutral atom, the atomic number is also equal to the number of electrons. 2️⃣ Mass Number (A): It is the total number of protons and neutrons (nucleons) in the nucleus of an atom. The number of neutrons in an atom can be calculated by subtracting the atomic number from the mass number. Number of Neutrons = Mass Number - Atomic Number Q2: If an atom has a mass number of 11 and an atomic number of 5, how many neutrons does it have? 📚 Exam Tip 📚 In the Periodic Table, each element is represented with its mass number and atomic number. This notation helps us understand the structure of the atom for that particular element. Stay tuned for more lessons where we delve deeper into the Periodic Table and explore the properties and behaviors of atoms! 💥🔬📚 Quiz Level 1: Beginner Level 🌱 What is the smallest part of an element that can participate in chemical reactions? 🤔 Where are protons and neutrons found in an atom? 📍 What is the charge of an electron? ⚡ What do we call the particles that an atom is made up of? 🎭 What is the relative mass of an electron compared to protons and neutrons? ⚖️ Answers: An atom. In the nucleus of an atom. Negative. Subatomic particles. The mass of an electron is often considered negligible, being around 1/1836 times smaller than that of protons and neutrons. Level 2: Novice Explorer 🧭 Quiz What are the charges of protons, neutrons, and electrons, respectively? 🌈 What does the atomic number of an atom tell us? 🔢 What is the term for protons and neutrons together? 🤝 How can we calculate the number of neutrons in an atom? 🧮 What is the space called that electrons move around in, outside the nucleus? 🌌 Answers: Protons have a positive charge, neutrons have no charge (neutral), and electrons have a negative charge. The atomic number tells us the number of protons in the nucleus of an atom. Protons and neutrons together are called nucleons. The number of neutrons = mass number - atomic number. This space is called the electron cloud or orbitals. ⚛️ Level 3 Questions: Structure of an Atom ⚛️ : Practicing More 💪 🔬💫 Level 3: Structure of an Atom 💫🔬 Describe the structure of an atom, giving details of the subatomic particles present. [6] Explain the terms atomic number and nucleon number. [2] 💡 Atomic Number (Z) - The atomic number represents the number of protons in an atom's nucleus, determining its unique identity. 🎯 💡 Nucleon Number (A) - The nucleon number, also known as the mass number, signifies the total number of protons and neutrons in the nucleus. 🔢 Copy and complete the table: 📋 [2] Explain why atoms are neutral. [1] An oxygen atom has 8 protons in its nucleus. Explain why it cannot have 9 protons. [1] When calculating the relative mass of an atom, the electrons are not used in the calculation. Explain why not. [1] 🌟💡 Level 3 Answers: Structure of an Atom 💡🌟 The structure of an atom revolves around its nucleus, containing protons and neutrons, while electrons occupy energy levels or shells surrounding the nucleus. Protons bear a positive charge, neutrons are neutral, and electrons carry a negative charge. ⚛️ Atomic Number (Z) signifies the count of protons, determining the element's identity. It corresponds to the number of electrons in a neutral atom. 💫 Nucleon Number (A) accounts for the total protons and neutrons present in the nucleus, representing the atom's mass. 📊 Atoms are neutral since they possess an equal number of positively charged protons and negatively charged electrons. This balance of charges yields an overall neutral charge. ⚖️ An oxygen atom with 8 protons cannot have 9 protons since the number of protons defines its identity as oxygen. Altering the proton count would result in a different element. 🚫 When calculating the relative mass of an atom, electrons are not considered due to their significantly smaller mass compared to protons and neutrons. An electron's mass is approximately 1/1836 amu, whereas protons and neutrons have a mass close to 1 amu. Consequently, electrons have a negligible impact on the overall mass calculation. ⚖️❌ Stay tuned for more exciting lessons on the atomic world and its mesmerizing phenomena! 🌌🔬✨ Quiz Level 4: Pro Player 🏅 If an atom's mass number is 12 and its atomic number is 6, how many neutrons does it have? 🧠 Why is an atom mainly empty space? 🌌 Can the number of protons in an atom change? Why or why not? 🔄 What is the role of electrons in chemical reactions? ⚗️ If an atom gains an electron, does it become positively or negatively charged? Why? 🎭 Answers: The atom has 6 neutrons (mass number - atomic number = 12 - 6). An atom is mainly empty space because the electrons orbit the nucleus in this space, and electrons are much smaller than the nucleus. The number of protons in an atom cannot change, as changing the number of protons would change the identity of the element (its atomic number). Electrons participate in chemical bonds, either being transferred (ionic bonds) or shared (covalent bonds) between atoms. If an atom gains an electron, it becomes negatively charged because electrons carry a negative charge. Quiz Level 5: Expert Challenger 🏆 What determines the identity of an element? 🔎 How does the arrangement of electrons impact the chemical properties of an atom? 🌈 How does the atomic number affect the position of an element in the periodic table? 📚 What happens to the charge of an atom if it loses an electron? Why? 🎭 If an atom's mass number is 14 and it has 7 neutrons, what is its atomic number? 🧮 Answers: The number of protons (atomic number) in an atom determines the identity of an element. The arrangement of electrons, especially those in the outermost shell (valence electrons), impacts the chemical properties of an atom as they are involved in bonding. The atomic number determines the position of an element in the periodic table; elements are arranged in order of increasing atomic number. If an atom loses an electron, it becomes positively charged because it loses a negatively charged particle. The atom has an atomic number of 7 (mass number - number of neutrons = 14 - 7).

9f61eea9-b517-46ae-a62d-2d02c62243b5 Know that in for endothermic reactions H products > H reactants, ∆ H> 0 and reaction absorbs energy Grade 10 SABIS In chemical reactions, an endothermic reaction is one that absorbs energy from the surroundings. It is characterized by the fact that the enthalpy (H) of the products is greater than the enthalpy of the reactants. This change in enthalpy (∆H) is positive, indicating that energy is absorbed during the reaction. To understand endothermic reactions, let's consider an everyday example: the process of cooking pasta. When you boil water and add pasta to it, the reaction between the pasta and the hot water is endothermic. The energy from the heat source is absorbed by the pasta, causing it to cook and increase in temperature. In an endothermic reaction, the potential energy of the products is higher than that of the reactants. This means that the reactants have a lower energy level compared to the products. As the reaction progresses, energy is absorbed from the surroundings, leading to an increase in potential energy. On a potential energy diagram for an endothermic reaction, the reactants are represented at a lower energy level compared to the products. The curve starts at a lower point (representing the energy of the reactants) and gradually increases (representing the increase in potential energy) as the reaction proceeds towards the products. The difference in potential energy between the reactants and products is the amount of energy absorbed from the surroundings. The positive value of ∆H indicates that the reaction absorbs energy. This energy can be in the form of heat, light, or any other form of energy. In the case of the cooking pasta example, the absorbed energy is in the form of heat from the boiling water. Endothermic reactions are essential in various processes. For instance, in photosynthesis, plants absorb energy from sunlight to convert carbon dioxide and water into glucose and oxygen. This process requires energy input to drive the reaction. Another example is the process of evaporation. When a liquid evaporates, it absorbs energy from the surroundings, causing a cooling effect. This is because the liquid particles need to gain energy to break the intermolecular forces and transform into a gas state. Endothermic reactions are also prevalent in chemical reactions used for cooling, such as instant cold packs or ice packs. These packs contain chemicals that undergo an endothermic reaction when activated, absorbing heat from the surroundings and providing a cooling sensation. In summary, endothermic reactions are characterized by the absorption of energy from the surroundings. The enthalpy of the products is greater than that of the reactants, resulting in a positive change in enthalpy (∆H). On a potential energy diagram, the potential energy increases from the reactants to the products, indicating the energy absorbed during the reaction. Understanding endothermic reactions helps us comprehend processes that require energy input and have a cooling effect, such as cooking, photosynthesis, evaporation, and cooling packs.

6b4d40ef-0011-442b-b2d6-ae15b26f0831 Sublimation The process of a substance changing directly from a solid to a gaseous state at a specific temperature.

37826294-3bce-4e63-98ad-5e0f89c2dfca Conservation of Mass Grade 10 SABIS SABIS In chemical reactions, the total mass of the reactants is equal to the total mass of the products. This principle states that matter cannot be created or destroyed.

3368b554-6764-42d8-8f1e-81bb53feca19 Volume at STP Grade 10 SABIS SABIS 1.00 mole of ANY gas occupies 22.4 dm3