6. Chemical reactions
A section of Chemistry, 0620
Listing 10 of 905 questions
The table shows some properties of four substances, A, B, C and D. substance melting point / °C does the solid conduct electricity? does a solution of the solid conduct electricity? A yes does not dissolve B no dissolves and conducts C no does not dissolve D no does not dissolve Which one of these substances has a giant covalent structure, a simple molecular structure, a metallic structure? A student carried out an experiment to determine the rate of reaction of calcium carbonate with excess hydrochloric acid. CaCO3+ 2HCl → CaCl 2+ CO2+ H2OHe recorded the loss of mass of the reaction mixture over a period of time. 362.05 cotton wool small pieces of calcium carbonate balance hydrochloric acid Explain why the reaction mixture decreases in mass. He carried out the reaction at constant temperature using 2 g of calcium carbonate in small pieces. The hydrochloric acid was in excess. He plotted his results on a grid. This is shown below. 1.0 0.8 0.6 0.4 0.2 time / seconds loss in mass / g At what time has the reaction just fi nished? s From the graph, deduce the loss in mass in the fi rst 100 seconds. g The student repeated the experiment keeping everything the same except for the size of the pieces of calcium carbonate. He used smaller pieces of calcium carbonate but the mass used was the same. On the grid above, draw a line to show how the loss of mass changes with time when smaller pieces of calcium carbonate are used. State the effect of increasing the concentration of hydrochloric acid on the rate of this reaction when all other factors remain constant.
0620_s13_qp_21
THEORY
2013
Paper 2, Variant 1
View
Hydrogen peroxide, H2O2, decomposes in the presence of an enzyme called peroxidase. The products of this reaction are water and oxygen. What is meant by the term enzyme? Complete the symbol equation for this reaction. H2O2 → 2H2O + O2 A student followed the course of this reaction by measuring the volume of oxygen released over a period of time. The diagram below shows some results that he obtained using hydrogen peroxide at three different concentrations. volume of oxygen / cm3 time / seconds concentration of H2O2 0.4 mol / dm3 0.2 mol / dm3 0.1 mol / dm3 Describe how the concentration of hydrogen peroxide affects the rate of this reaction. On the graph above, draw a line to show the course of the reaction when the starting concentration of hydrogen peroxide is 0.3 mol / dm3. For the concentration of hydrogen peroxide of 0.4 mol / dm3, deduce ● the volume of oxygen given off when the reaction is complete, cm3 ● the time it takes to produce 14 cm3 of oxygen. seconds In the presence of sulfuric acid, hydrogen peroxide reacts with iodide ions to form iodine and water. This involves the reduction of hydrogen peroxide. What is the meaning of the term reduction ? Complete the word equation for the reaction of sulfuric acid with calcium hydroxide. sulfuric acid + calcium hydroxide → + Describe a test for iodide ions. test result
0620_s13_qp_23
THEORY
2013
Paper 2, Variant 3
View
A small piece of marble, CaCO3, was added to 5.0 cm3 of hydrochloric acid, concentration 1.0 mol / dm3, at 25 °C. The time taken for the reaction to stop was measured. The experiment was repeated using 5.0 cm3 of different solutions of acids. The acid was in excess in all of the experiments. Typical results are given in the table. experiment temperature / °C acid solution time / min hydrochloric acid 1.0 mol / dm3 hydrochloric acid 0.5 mol / dm3 ethanoic acid 1.0 mol / dm3 hydrochloric acid 1.0 mol / dm3 Explain why it is important that the pieces of marble are the same size and the same shape. How would you know when the reaction had stopped? The equation for the reaction in experiment 1 is: CaCO3+ 2HCl → CaCl 2+ CO2+ H2OComplete the following ionic equation. CaCO3+ 2H+→ + + Explain why the reaction in experiment 1 is faster than the reaction in experiment 2. The acids used for experiment 1 and experiment 3 have the same concentration. Explain why experiment 3 is slower than experiment 1. Explain in terms of collisions between reacting particles why experiment 4 is slower than experiment 1.
0620_s13_qp_31
THEORY
2013
Paper 3, Variant 1
View
One of the factors which determine the reaction rate of solids is particle size. A mixture of fi nely powdered aluminium and air may explode when ignited. An explosion is a very fast exothermic reaction. This causes a large and sudden increase in temperature. Explain each of the following in terms of collisions between reacting particles. Why is the reaction between fi nely powdered aluminium and air very fast? Explain why for most reactions the rate of reaction decreases with time. Suggest an explanation why the rate of reaction in an explosion could increase rather than decrease with time. Give another example of a substance other than a metal which, when fi nely powdered, might explode when ignited in air. Describe a simple test-tube reaction which shows the effect of particle size on the rate at which a solid reacts with a solution.
0620_s13_qp_33
THEORY
2013
Paper 3, Variant 3
View
Questions Discovered
905