0620_s21_qp_41
A paper of Chemistry, 0620
Questions:
7
Year:
2021
Paper:
4
Variant:
1
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Potassium reacts with chlorine to form potassiumchloride, KCl. Write a chemical equation for this reaction. Potassiumchloride is an ionic compound. Complete the diagram to show the electron arrangement in the outer shells of the ions present in potassium chloride. Give the charges on both ions. K Cl  Molten potassiumchloride undergoes electrolysis. State what is meant by the term electrolysis. Name the products formed at the positive electrode and negative electrode when molten potassiumchloride undergoes electrolysis. anode cathode  Concentrated aqueous potassiumchloride undergoes electrolysis. Write an ionic half-equation for the reaction at the negative electrode . Name the product formed at the positive electrode . Name the potassium compound that remains in the solution after electrolysis. Complete the dot-and-cross diagram to show the electron arrangement in a molecule of chlorine, Cl 2. Show the outer electrons only. Cl Cl  The melting points and boiling points of chlorine and potassium chloride are shown. melting point / °C boiling point / °C chlorine –101 –35 potassium chloride Deduce the physical state of chlorine at –75 °C. Use the data in the table to explain your answer. physical state explanation  Explain, in terms of structure and bonding, why potassiumchloride has a much higher melting point than chlorine. Your answer should refer to the: ● types of particle held together by the forces of attraction ● types of forces of attraction between particles ● relative strength of the forces of attraction. 
4. Electrochemistry  →  4.1. Electrolysis
9. Metals  →  9.4. Reactivity series
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Dinitrogentetroxide, N2O4, decomposes into nitrogendioxide, NO2. The reaction is reversible. N2O42NO2colourless gas brown gas A gas syringe containing a mixture of dinitrogentetroxide and nitrogendioxide gases was sealed and heated. After reaching equilibrium the mixture was a pale brown colour. end sealed plunger mixture of dinitrogen tetroxide and nitrogen dioxide State what is meant by the term equilibrium. The plunger of the gas syringe is pushed in. The temperature does not change. The mixture initially turns darker brown. After a few seconds the mixture turns lighter brown because the equilibrium shifts to the left. N2O42NO2colourless gas brown gas Explain why the mixture initially turns darker brown. Explain why the position of equilibrium shifts to the left. The forward reaction is endothermic. State what happens to the position of equilibrium when the temperature of the mixture is increased. State what happens to the rate of the forward reaction and the rate of the backward reaction when the temperature of the mixture is increased. rate of the forward reaction rate of the backward reaction  
6. Chemical reactions  →  6.3. Reversible reactions and equilibrium
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This question is about salts. Salts that are insoluble in water are made by precipitation. ● Lead(iodide, PbI2, is insoluble in water. ● All nitrates are soluble in water. ● All sodium salts are soluble in water. You are provided with solid lead(nitrate, Pb(NO3)2, and solid sodiumiodide, NaI. Describe how you would make a pure sample of lead(iodide by precipitation. Your answer should include: ● practical details ● a chemical equation for the precipitation reaction. Nitrates decompose when heated. When hydrated zincnitrate is heated, oxygen gas is given off. Describe a test for oxygen. test observations  Complete the equation for the decomposition of hydrated zincnitrate. 2Zn(NO3)2•6H2O → ZnO + NO2 + O2 + H2O Some sulfates are hydrated. When hydrated sodiumsulfate crystals, Na2SO4•xH2O, are heated, they give off water. Na2SO4•xH2O→ Na2SO4+ xH2OA student carries out an experiment to determine the value of x in Na2SO4•xH2O. step 1 Hydrated sodiumsulfate crystals are weighed. step 2 The hydrated sodiumsulfate crystals are then heated. step 3 The remaining solid is weighed. Describe how the student can check that all the water has been given off. In an experiment, 1.61 g of Na2SO4•xH2O is heated until all the water is given off. The mass of Na2SO4 remaining is 0.71 g. [Mr: Na2SO4,142; H2O,18] Determine the value of x using the following steps. ● Calculate the number of moles of Na2SO4 remaining.  mol ● Calculate the mass of H2O given off.  g ● Calculate the number of moles of H2O given off.  mol ● Determine the value of x.  x =  
7. Acids, bases and salts  →  7.3. Preparation of salts
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This question is about iron. Iron is extracted from its main ore in a blast furnace. waste gases raw materials: coke, iron ore, limestone molten iron A B Name the main ore of iron used in the blast furnace. Name the substance that enters the blast furnace at A. Name the substance that leaves the blast furnace at B. Give two reasons for using coke in the blast furnace.  Another ore of iron is iron pyrites, FeS2. Iron pyrites contains the positive ion, Fe2+. Deduce the formula of the negative ion in FeS2. Iron is a transition element. A list of properties of iron is shown. ● Iron is a good conductor of electricity. ● Iron forms soluble salts. ● Iron forms coloured compounds. ● Iron has variable oxidation states. ● Iron acts as a catalyst. ● Iron forms a basic oxide. Give two properties from the list in which iron differs from GroupI elements.  Give two properties from the list in which iron is similar to GroupI elements.  Steel consists mainly of iron. Iron forms rust when it reacts with water and oxygen. Magnesium blocks can be attached to the bottom of steel boats. The magnesium does not completely cover the steel. water containing dissolved oxygen magnesium blocks steel boat Explain how the magnesium blocks prevent iron from rusting. Explain why replacing the magnesium blocks with copper blocks will not prevent the bottom of the boat from rusting. 
9. Metals  →  9.6. Extraction of metals
9. Metals  →  9.5. Corrosion of metals
9. Metals  →  9.4. Reactivity series
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Many organic compounds contain carbon, hydrogen and oxygen only. An organic compound V has the following composition by mass. C, 48.65%; H, 8.11%; O, 43.24% Calculate the empirical formula of compound V.  empirical formula = CompoundW has the empirical formula CH4O and a relative molecular mass of 32. Calculate the molecular formula of compoundW.  molecular formula = Compounds X and Y have the same general formula. X and Y are both carboxylic acids. CompoundX has the molecular formula C2H4O2. CompoundY has the molecular formula C4H8O2. Deduce the general formula of compounds X and Y. Draw the structure of compoundY. Show all of the atoms and all of the bonds. Name compoundY. name  Give the name used to describe a ‘family’ of similar compounds with the same general formula, similar chemical properties and the same functional group. Propene is an unsaturated hydrocarbon. The formula of propene is shown. CH3CH=CH2 State the colour change observed when propene is added to aqueous bromine. from to Propene can be produced by cracking long chain alkanes. Pentadecane, C15H32, is cracked to produce an alkane and propene in a 1 : 2 molar ratio. Complete the chemical equation for this reaction. C15H32 → +  Propene can be converted into poly. Name the type of polymerisation that occurs when propene is converted into poly. Complete the diagram to show a section of poly. C C C C  
11. Organic chemistry  →  11.2. Naming organic compounds
3. Stoichiometry  →  3.1. Formulae
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