NYGH O’ Level Database Questions for Practice and Revision Chemistry

1 Chem!stry Name: …………………… ( ) Class: ……………… Date: …… / …… / …… O’ Level Database Questions for Practice and Revision • Note: A link to the answers is given on pg. 47. A copy of the Periodic Table is given on pg. 48. Question 1. This graph shows how the percentage of three of the gases in the Earth’s atmosphere has changed over five thousand million years. Use the information from the graph to answer the following questions. (a) (i) How long have the percentages of all gases in the atmosphere remained unchanged? …………………………………………………………………………………………………… (ii) Name gas 3. Give a reason for your answer. [3] …………………………………………………………………………………………………… ……………………………………………………………………………………………………

2 (b) (i) Describe how the percentages of carbon dioxide and oxygen have changed. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… (ii) Suggest an explanation for the changes that have taken place in carbon dioxide and oxygen percentages, identifying the processes involved and giving equations for any reactions. [7] …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… [Total: 10]

3 Question 2. Read the information about the chlorides of the elements in Period 3 of the Periodic Table. Elements and their Chlorides The formulae and chemical properties of the chlorides of the elements change across Period 3. The chlorides behave differently when they are added to water. Some of the chlorides dissolve in water to form a solution. Some hydrolyse when they are added to water. This means that they react chemically with water to produce new products. element metal or non- metal formula of main chloride bonding in chloride effect of adding chloride to water products of adding chloride to water Na metal NaCl ionic dissolves NaCl(aq) Mg metal MgCl2 ionic dissolves MgCl2(aq) Al metal AlCl3 covalent hydrolyses complex mixture of products including HCl(aq) Si non-metal SiCl4 covalent hydrolyses SiO2(s) HCl(aq) P non-metal PCl3 covalent hydrolyses H3PO3(aq) HCl(aq) S non-metal S2Cl2 covalent hydrolyses complex mixture of products including HCl(aq) Cl non-metal Cl2 covalent hydrolyses HClO(aq) HCl(aq) The reaction of chlorine with water is interesting because it is an example of a disproportionation reaction. Disproportionation happens when the oxidation state of the same element both increases and decreases in the reaction. The chlorides have different formulae and the ratio of the element to chlorine changes across Period 3. Some examples are shown in the table below. formulae of chloride ratio of element to chlorine NaCl 1:1 MgCl2 1:2 AlCl3 1:3

4 (a) Describe the pattern for the ratio of each element to chlorine across Period 3. Include ratios in your answer. [2] ………………………………………………………………………………………………………... ………………………………………………………………………………………………………... ………………………………………………………………………………………………………... ………………………………………………………………………………………………………... (b) (i) Which chloride forms a precipitate when added to water? [1] …………………………………………………………………………………………………… (ii) Write a balanced equation for the reaction of phosphorus(III) chloride with water. [1] …………………………………………………………………………………………………… (c) Use ideas about oxidation states to explain why the reaction of chlorine with water is a disproportionation reaction. [2] ………………………………………………………………………………………………………... ………………………………………………………………………………………………………... ………………………………………………………………………………………………………... ………………………………………………………………………………………………………... (d) Two students talk about the data. Student 1: “I think that whether or not the chloride hydrolyses is linked to the metal or non-metal character of the chloride.” Student 2: “I think that whether or not the chloride hydrolyses is linked to the bonding of the chloride.” Does the information in the table support the ideas of the students? Explain your reasoning. [3] ………………………………………………………………………………………………………... ………………………………………………………………………………………………………... ………………………………………………………………………………………………………... ………………………………………………………………………………………………………... (e) Another student performs an experiment to test whether some other chlorides dissolve or hydrolyse when they are added to water. She adds each chloride to water and tests the pH of the mixture. Explain how the result of a pH test shows whether or not the chloride has hydrolysed. [2] ………………………………………………………………………………………………………... ………………………………………………………………………………………………………... ………………………………………………………………………………………………………...

5 (f) Suggest a reason why argon is not included in the table of information about Period 3 chlorides. [1] ………………………………………………………………………………………………………... ………………………………………………………………………………………………………... [Total: 12] Question 3. A series of experiments were carried out to investigate the effect of different catalysts on the rate of a reaction. The table shows the time taken for the reaction to finish when different metal compounds were used as catalysts. The metal compounds contain Group 1 metals, Group 2 metals or transition metals. experiment catalyst temperature at start / C time taken for reaction to finish / s 1 NaCl 19 45 2 FeCl2 20 22 3 CoCl2 19 26 4 MgCl2 20 46 5 NaNO3 19 45 6 Fe(NO3)2 20 22 7 Fe(NO3)3 19 15 8 Co(NO3)2 19 26 9 Mg(NO3)2 19 46 (a) Explain why it is important to take note of the temperature at the start of the reaction. [1] ………………………………………………………………………………………………………... ………………………………………………………………………………………………………... (b) Group 1 and Group 2 metal compounds are less effective than transition metal compounds as catalysts. Explain how the information in the table supports this statement. [2] ………………………………………………………………………………………………………... ………………………………………………………………………………………………………... ………………………………………………………………………………………………………... ………………………………………………………………………………………………………...

6 (c) Two different iron ions were used in the experiment. (i) Give the formulae for the two ions. [1] …………………………………………………………………………………………………… (ii) Which iron ion seems to be the more effective catalyst? Explain your reasoning. [2] …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… (d) A student wrote this conclusion from the results in the table. The type of anion in the c