IGCSE 2020 4CH1/2C January Edexcel Chemistry

IGCSE 2020 4CH1/2C January (pdf)

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1. This question is about elements, compounds and mixtures.
   (a) Name the element that burns with a lilac flame
   (b) Name the technique used to separate the mixture of colours in black ink.
   (c) The box gives the names of some substances
   Choose substances from the box to answer these questions.
   (i) Identify the compound.
   (ii) Identify the mixture
   (iii) Identify the non-metal element that is a solid at room temperature.
2. Crude oil is a mixture of hydrocarbons.
   (a) Name the process used to separate crude oil into fractions
   (b) Give one use of the kerosene fraction.
   (c) One of the hydrocarbons in the refinery gas fraction is an alkane with the structural formula CH₃CH₂CH_{32/sub>CH3
   (i) Give the name of this alkane.
   (ii) Calculate the relative molecular mass (Mr) of this alkane.
   (d) One of the alkanes in the gasoline fraction has the displayed formula
   (i) Determine the molecular formula of this alkane.
   (ii) Give the general formula for the alkanes.
   (e) Catalytic cracking is used to convert long-chain alkanes into shorter-chain alkanes.
   (i) Name the catalyst used in catalytic cracking
   (ii) Explain why it is necessary to convert long-chain alkanes into shorter-chain alkanes.
   (f) Catalytic cracking also produces alkenes.
   C11H24 can undergo cracking to give pentane (C5H12) and two different alkenes.}
   
3. This question is about copper and its compounds.
   (a) Copper is a metal used for electrical wiring.
   Explain why copper is a good conductor of electricity
   Complete the equation for this cracking reaction.
   (b) This apparatus is used to investigate the electrolysis of copper(II) sulfate solution with graphite electrodes.
   Copper forms at the negative electrode and oxygen forms at the positive electrode.
   (i) State what would be observed at each electrode.
   (ii) The ionic half-equation for the reaction at the negative electrode is
   Cu²⁺ + 2e^– → Cu
   State why this is a reduction reaction.
   (c) When hydrated copper(II) sulfate crystals are heated, anhydrous copper(II) sulfate forms.
   A mass of 12.5g of hydrated copper(II) sulfate crystals is heated in a crucible until all the water of crystallisation is removed.
   A mass of 8.0g of anhydrous copper(II) sulfate forms.
   Show by calculation that the formula of hydrated copper(II) sulfate is CuSO₄.5H₂O
   [Mr of CuSO₄ = 159.5 Mr of H₂O = 18]

4. A student investigates the reaction between sodium hydroxide solution and dilute sulfuric acid.
   He does a titration to find the concentration of the sulfuric acid.
   This is his plan for the titration. There are some mistakes and omissions in his plan.
   

• rinse a conical flask with the sodium hydroxide solution
• use a measuring cylinder to measure out 25cm³ of the sodium hydroxide solution and add it to the conical flask
• add a few drops of methyl orange indicator to the conical flask
• rinse a burette with water and then fill it with the sulfuric acid
• add the acid from the burette to the conical flask until the indicator changes colour at the end‑point of the titration
• record the final burette reading
  (a) Give the colour change of the methyl orange indicator at the end-point.
  (b) Describe four changes that the student could make to improve his plan.
  (c) The student then does the titration correctly.
  He finds that 16.70cm³ of the dilute sulfuric acid neutralises 25.0cm³ of sodium hydroxide solution of concentration 0.200mol/dm³
  The equation for the reaction is
  2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O
  Calculate the concentration, in mol/dm³, of the sulfuric acid.

5. Oxygen can be prepared from hydrogen peroxide using a catalyst.
   (a) Which is a correct statement about oxygen?
   (b) Explain how a catalyst increases the rate of a reaction
   (c) The equation for the preparation of oxygen from hydrogen peroxide is
   2H₂O₂ → 2H₂O + O₂
   This equation can also be written using displayed formulae to show all the covalent bonds in the molecules.
   2H—O—O—H → 2H—O—H + O O
   The table gives the bond energies for these bonds
   (i) Use the values in the table to calculate the enthalpy change, ΔH, for the reaction. Include a sign in your answer
   (ii) Complete the energy level diagram to show the position of the products and the enthalpy change, ΔH, for the reaction.
6. Ethanol, C₂H₅OH, can be manufactured from ethene and steam using a phosphoric acid catalyst.
   (ii) Draw the displayed formula of ethanol
   (b) Ethanol burns in a plentiful supply of air to form carbon dioxide and water.
   (i) Give the chemical equation for this reaction.
   (ii) When the air supply is limited, incomplete combustion occurs and carbon monoxide forms.
   State why carbon monoxide is poisonous to humans.
   (c) When ethanol reacts with ethanoic acid, an ester forms.
   Give the name of this ester.
   (d) Butanedioic acid and ethanediol react together to form a polyester and water.
   (i) Give the name of this type of polymerisation
   (ii) Complete the equation.
   Show only one repeat unit of the polyester
7. This question is about some Group 2 elements and their compounds.
   (a) Calcium reacts with water to produce calcium hydroxide and hydrogen gas.
   (i) Give the word equation for this reaction.
   (ii) State two observations that would be made during this reaction.
   (b) (i) Describe how a pure, dry sample of the insoluble salt, barium sulfate, could be made from the two solids sodium sulfate and barium chloride
   (ii) Give an ionic equation for the reaction that occurs.
   Include state symbols in your equation.
   (c) When magnesium nitrate is heated, magnesium oxide, nitrogen dioxide and oxygen form.
   The equation for the reaction is
   2Mg(NO₃)₂(s) → 2MgO(s) + 4NO₂(g) + O₂(g)
   (i) What is the name for this type of reaction?
   (a) (i) State the temperature and pressure used in this manufacturing process.
   (ii) Calculate the total volume, in dm³, of gas produced at rtp when 7.7g of magnesium nitrate completely reacts.
   [Assume that the molar volume of a gas at rtp is 24dm³]
   [Mr of Mg(NO₃)₂ = 148]
   Give your answer to two significant figures.

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