Chemistry WCH12 January 2021 Questions & Answers

Questions And Worked Solutions For Chemistry WCH12 January 2021

IAL Chemistry WCH12 January 2021 Questions - Complete Paper (pdf)

1. The energy profile for a reaction is shown.
   What is the minimum energy needed for this reaction to occur?
2. Which of these isomers with the formula C₈H₁₈ has the lowest boiling temperature?
3. Which of these pure compounds has hydrogen bonding in the liquid state?
4. The hydrogen ion, H⁺, bonds to a water molecule forming an H₃O⁺ ion.
5. The viscosities of four liquid organic compounds are compared by placing the liquids in separate identical tubes, each with an air bubble at the top.
6. This question is about the reaction of potassium iodide with concentrated sulfuric acid.
7. Iodate(V) ions, IO₃⁻, oxidise dithionate ions, S₂O₆²⁻, according to the equation
8. Magnesium reacts with hydrochloric acid.
9. Which of these compounds does not produce a colour in a flame test, and produces an alkaline gas when warmed with sodium hydroxide solution?
10. Which of these increases as Group 7 is descended?
11. The table shows the amount of energy released per gram when some alkanes are burned in excess oxygen under standard conditions
12. The enthalpy changes for two reactions are shown
13. What is the skeletal formula of 2-chloro-4,4-dimethylhexane?
14. Some alcohols react with concentrated phosphoric(V) acid, H₃PO₄ , to form alkenes.
15. Magnesium nitrate decomposes on heating.
16. How many moles are there in 15.1 cm³ of liquid propan-1-ol?
17. The oxidation of propan-1-ol by acidified potassium dichromate(VI) forms propanoic acid with a yield of 36 % by mass.
18. Barium chloride solution, BaCl₂(aq), reacts with gallium sulfate solution, Ga₂(SO₄)₃(aq) to form a precipitate of barium sulfate, BaSO₄(s).

19. Ethanol can be made in industry by the reaction of ethene with steam, using a phosphoric(V) acid catalyst.
    The reaction is carried out at 300°C and 60 atm. An initial yield of 5% is achieved when the ethene and steam first pass through the reactor.
    (a) Explain the chemical reasons for the conditions used and why such a low initial yield is acceptable in the industrial process.
    (b) The product of the reaction is a mixture of ethanol and water.
    Explain why ethanol and water mix together fully.
    You may find it helpful to draw a diagram.
    (c) Ethanol can be oxidised using a solution of acidified potassium dichromate(VI), K₂Cr₂O₇(aq).
    Ethanoic acid and another organic compound, Y, are both possible products
20. The compound DMAA was originally synthesised as a decongestant.
    A suggested synthetic route for DMAA is shown.
    (a) (i) Give the systematic name of compound A.
    (ii) Identify, by name or formula, a suitable reagent for Step 1.
    (iii) Give the mechanism for the reaction in Step 2.
    Include curly arrows, and any relevant dipoles and lone pairs.
    (b) DMAA is only slightly soluble in water but dissolves readily in hydrochloric acid to form an aqueous solution
    (i) Explain the type of bonding that occurs between the nitrogen atom and the hydrogen ion, when the positive ion forms.
    (ii) Complete the diagrams to show how the ions formed in the reaction between DMAA and hydrochloric acid interact with water molecules.
21. This question is about ethanoic acid and some related salts. (a) A test to confirm the presence of an aqueous acid is adding a small amount of solid sodium carbonate to the solution. Describe two observations you would see in this test. (b) Sodium ethanoate is a component of reusable hand warmers. In use, a supersaturated solution of sodium ethanoate recrystallises to form solid hydrated sodium ethanoate, releasing energy (c) Ammonium ethanoate, CH₃COONH₄(s), is used to control the pH of foods. It can be formed by the reaction of pure ethanoic acid, CH₃COOH(l), with ammonium carbonate, (NH₄)2CO₃(s). Calculate the standard enthalpy change for this reaction by completing the Hess cycle and using the data shown. (d) Ammonium carbonate, (NH₄)2CO₃ , is an ingredient in cleaning solutions for camera lenses. These are aqueous solutions which contain no more than 1.8 g of ammonium carbonate in 100 cm³ of solution. Calculate the maximum concentration, in mol dm−3, of ammonium carbonate in such a solution
22. Potassium chlorate(V), KClO3 , is a crystalline solid used in fireworks. It is produced by the Liebig Process in two stages

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