6. Chemical reactions
A section of Chemistry, 0620
Listing 10 of 905 questions
Hydrogen peroxide decomposes to form water and oxygen. This reaction is catalysed by manganese(oxide. 2H2O2→ 2H2O+ O2The rate of this reaction can be investigated using the following apparatus. aqueous hydrogen peroxide and manganese(oxide oxygen gas 40 cm3 of aqueous hydrogen peroxide was put in the fl ask and 0.1 g of small lumps of manganese(oxide was added. The volume of oxygen collected was measured every 30 seconds. The results were plotted to give the graph shown below. volume of oxygen time t1 t2 t3 How do the rates at times t1, t2 and t3 differ? Explain the trend in reaction rate that you described in . The experiment was repeated using 0.1 g of fi nely powdered manganese(oxide. All the other variables were kept the same. On the axes opposite, sketch the graph that would be expected. Explain the shape of this graph. Describe how you could show that the catalyst, manganese(oxide, was not used up in the reaction. Manganese(oxide is insoluble in water. In the fi rst experiment, the maximum volume of oxygen produced was 96 cm3 measured at r.t.p. Calculate the concentration of the aqueous hydrogen peroxide in mol / dm3. 2H2O2→ 2H2O+ O2number of moles of O2 formed = number of moles of H2O2 in 40 cm3 of solution = concentration of the aqueous hydrogen peroxide in mol / dm3 =
0620_s14_qp_31
THEORY
2014
Paper 3, Variant 1
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Propanoic acid is a carboxylic acid. Its formula is CH3–CH2–COOH. Propanoic acid is the third member of the homologous series of carboxylic acids. Give the name and structural formula of the fourth member of this series. name formula Members of a homologous series have very similar chemical properties. State three other characteristics of a homologous series. Carboxylic acids can be made by the oxidation of alcohols. Draw the structural formula of the alcohol which can be oxidised to propanoic acid. Show all atoms and bonds. Name a reagent, other than oxygen, which can oxidise alcohols to carboxylic acids. Complete the following equations for some of the reactions of propanoic acid. The salts of this acid are called propanoates. zinc + propanoic acid → + hydrogen calcium + propanoic → + oxide acid LiOH + CH3CH2COOH → + A piece of magnesium was added to 100 cm3 of an aqueous acid. The time taken for the metal to react completely was measured. This experiment was repeated using different aqueous acids. The same volume of acid was used in each experiment and the pieces of magnesium used were identical. In one experiment the reaction was carried out at a different temperature. experiment acid concentration in mol / dm3 temperature / °C time / minutes A propanoic 1.0 B propanoic 1.0 C propanoic 0.5 D hydrochloric 1.0 Explain the following in terms of collision rate between reacting particles. Why is the rate in experiment C slower than the rate in experiment A? Why is the rate in experiment B faster than the rate in experiment A? Why is the rate in experiment D faster than the rate in experiment A?
0620_s14_qp_32
THEORY
2014
Paper 3, Variant 2
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Questions Discovered
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