Chemistry WCH15 January 2021 Questions & Answers

Questions & Worked Solutions For Chemistry WCH15 January 2021

IAL Chemistry WCH15 January 2021 Questions - Complete Paper (pdf)

1. When an alkene is added to a solution of potassium manganate(VII), the purple solution turns colourless. In terms of electron transfer and oxidation number, how does the manganese change in this reaction?
2. The standard hydrogen electrode uses an electrode of platinum coated in a finely divided form of the metal called platinum black. What is the purpose of this coating?
3. An electrochemical cell is set up to measure E cell for the reaction
4. Hydrogen-oxygen fuel cells can operate in acidic or alkaline conditions. What is the reaction at the anode in an alkaline hydrogen-oxygen fuel cell?
5. Which of these has the greatest number of unpaired electrons in each of its atoms?
6. Nickel is classified as a transition metal. This is because nickel
7. Platinum forms a complex with the formula Pt(NH₃)₂Cl₂ and chromium forms a complex with the formula CrCl4⁻.
   (a) What are the shapes of these complexes?
8. Cobalt chloride is used as a test for the presence of water. This test depends on the fact that
9. Iodide ions are oxidised by peroxodisulfate ions in aqueous solution.
10. The delocalised electrons in benzene result from the overlap of
11. The reaction of ethene with bromine occurs under normal laboratory conditions but the reaction of benzene with bromine to form bromobenzene requires heat and the presence of a catalyst. The best explanation for the difference in reactivity is that the delocalised electrons in benzene
12. What is the name of the compound shown?
13. Separate 0.1 mol dm⁻³ aqueous solutions of ammonia, butylamine and phenylamine were prepared. Which of the following sequences shows the solutions in order of increasing pH?
14. The repeat unit of a polymer is shown
15. The repeat unit of a polymer is shown
16. The structure of a hydrocarbon is shown What is the maximum oxidation number shown in compounds of this element?
17. When a sample of a hydrocarbon is burned completely in oxygen, 2.64 g of carbon dioxide and 0.81 g of water are formed. Which of these could be the molecular formula of the hydrocarbon?
18. Benzenecarboxylic acid may be produced from benzene in a two-step synthesis.

19. The diagram summarises some reactions of copper compounds
20. Ketones are useful starting compounds in organic synthesis.
    This question is about butanone.
    (a) The mass spectrum of butanone has significant peaks at m/ z = 43 and at m/ z = 57.
    (i) Give the structures of the species responsible for these two peaks
    (ii) Give the structure of one other species that you would expect to produce a peak at a different m/ z value in the mass spectrum of butanone.
    (b) Devise a reaction scheme to prepare propan-1-ol from butanone, using no more than four steps.
    Identify the reagents and essential conditions for each step and give the name or structure of each of the intermediate compounds.
    (c) Devise a reaction scheme to prepare 2-methylbut-2-ene from butanone, using no more than four steps.
    Identify the reagents and essential conditions for each step and give the name or structure of each of the intermediate compounds.
21. A yellow crystalline solid E dissolved in distilled water to give a yellow solution. Addition of dilute sulfuric acid to this solution produced an orange solution F. Warming F with ethanol resulted in a green solution G, and the formation of ethanal. A standard cell was set up using solutions of F and G for the right-hand electrode and ethanol and ethanal for the left-hand electrode. E cell was found to be +1.94 V
22. Using excess oxygen, 25 cm³ of a gaseous hydrocarbon CxHy was burned completely. After cooling to room temperature the total gas volume was measured and found to be 75 cm³ less than the total gas volume before the mixture was ignited. When the product gases were shaken with potassium hydroxide solution, the total gas volume decreased by a further 100 cm³. All gas volumes were measured at room temperature and pressure.
23. Compare and contrast the mechanism of the action of platinum as a catalyst in the removal of pollutants from car engine exhaust fumes with that of vanadium(V) oxide as a catalyst in the Contact Process for the manufacture of sulfuric acid. General definitions of catalysts are not required.
24. There are over a thousand chemical compounds in coffee and their physiological effects are the subject of considerable speculation and research. The verdict on coffee is contradictory: some of the compounds have been identified as toxic and even carcinogenic but others are antioxidants associated with cancer prevention. Recent research has identified compounds in coffee that might be used in the treatment of prostate cancer. By far the best known compound in coffee is caffeine, the most widely consumed psychoactive drug in the world. In small amounts it is a stimulant but doses in excess of 10 g per day are toxic. Caffeine contains amide and amine groups.

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