OCR A Jan 2010 Paper 2 Q2

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2 Dilute aqueous hydrogen peroxide, H2O2(aq), is used to sterilise contact lenses. (a) Dilute H2O2(aq) slowly decomposes at room temperature to produce oxygen and water. The decomposition of H2O2(aq) can be made faster by:increasing the concentration of the H2O2(aq), adding a small amount of manganese(IV) oxide catalyst, heating the solution to 60 C. (i) Construct the equation for the decomposition of H2O2.[1] (ii) Explain why decomposition. increasing the concentration of H2O2(aq) increases the rate of[2] (iii) Explain how the catalyst can increase the rate of decomposition of H2O2(aq).[2]OCR 2010<br />
 (iv) Explain why increasing decomposition. the temperature of H2O2(aq) increases the rate of As part of your answer, you should add a second curve and any necessary labels to the Boltzmann distribution of molecular kinetic energies shown below. number of molecules with a given energy energy[3]OCR 2010 Turn over<br />
 (b) (i) In the past, hydrogen peroxide was manufactured by reacting barium peroxide, BaO2, with ice-cold dilute sulfuric acid. BaO2(s) + H2SO4(aq) BaSO4(s) + H2O2(aq) This method required the disposal of poisonous barium compounds. Calculate the atom economy for this manufacture of hydrogen peroxide from BaO2. Use the table of relative formula masses given below. compound relative formula mass BaO2 H2SO4 BaSO4 H2O2 169.3 98.1 233.4 34.0 atom economy =% [2]OCR 2010<br />
 (ii) Nowadays, hydrogen peroxide is manufactured using hydrogen gas, oxygen from the air and a substance called anthraquinone. stage 1 stage 2 H2 + anthraquinone anthraquinol O2 + anthraquinol H2O2 + anthraquinone Compare the manufacture of H2O2 from hydrogen and oxygen with the manufacture from barium peroxide described in b(i). Explain the advantages of the manufacture of H2O2 from hydrogen and oxygen.[3] (c) Some reactions of H2O2 are exothermic. Use ideas about the enthalpy changes that take place during bond breaking and bond making to explain why some reactions are exothermic.[2] [Total: 15]OCR 2010 Turn over<br />

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