XMS SEC 3 WA3 2023 QP

3 6092/Chemistry/2023 Term 3 Weighted Assessment Section A Answer all questions. Write your answers in the boxes provided at the end of the Section. 1 Which of the following shows the processes used to separate solid potassium nitrate crystals from sand? A dissolve in water → evaporate the filtrate → crystallise → filter B dissolve in water → filter → evaporate the filtrate → crystallise C filter → dissolve in water → evaporate the filtrate → crystallise D filter → evaporate the filtrate → dissolve in water → crystallise 2 Which of the following shows the correct ionic equation for the reaction between dilute nitric acid and zinc metal? A 2H+ + Zn → H2 + Zn2+ B H+ + OH− → H2O C Zn2+ + 2NO3− → Zn(NO3)2 D Zn2+ + 2H+ → H2 + Zn 3 1 Titration of an acid against a base is a method often used in the preparation of salts. 2 3 Which properties of the acid, the base and the salt are required if this method is to be used? acid base salt A insoluble insoluble insoluble B soluble insoluble insoluble C soluble soluble insoluble D soluble soluble soluble 4 A mixture of three liquids is separated by fractional distillation. Which statements are correct? 1 The liquid with the highest boiling point is collected first. 2 The liquid with the lowest boiling point is collected first. 3 The mixture boils at a constant temperature throughout the separation. 4 The temperature at which the mixture boils increases during the separation. A 1 and 3 B 1 and 4 C 2 and 3 D 2 and 4 4

4 6092/Chemistry/2023 Term 3 Weighted Assessment 5 The table below shows information about three indicators. indicator colour change pH at which colour changes methyl yellow red to yellow 3 bromocresol green yellow to blue 5 thymolphthalein colourless to blue 9 Which one of the following colours would be obtained for each indicator if it were added separately to pure water? methyl yellow bromocresol green thymolphthalein A red blue blue B red yellow blue C yellow blue colourless D yellow yellow colourless Question 1 2 3 4 5 Answer

5 6092/Chemistry/2023 Term 3 Weighted Assessment For Examiner’s Use Section B Answer all questions. Write your answers in the spaces provided. 6 Choose from the following substances to answer the questions. Al2O3 NaCl N2 Pb(NO3)2 SO2 Each substance may be used once, more than once or not at all. Select from the list above, (a) the amphoteric oxide(s). …………………………………………………………………..………………..…… [1] (b) the acidic oxide(s). …………………………………………………………………..………………..…… [1] (c) the compound that will react with dilute hydrochloric acid to form a precipitate. …………………………………………………………………..………………..…… [1] (d) the compound that can be prepared by titration. …………………………………………………………………..………………..…… [1] [Total: 4]

6 6092/Chemistry/2023 Term 3 Weighted Assessment For Examiner’s Use 7 Study the reaction scheme below. (a) Write down the identities of P, Q and R. P : …………………………………………... Q : …………………………………………... R : …………………………………………... [3] (b) Ammonia gas can also be made industrially by reacting nitrogen with hydrogen via the Haber process. The conditions required for this reaction are 450 oC and 250 atm with finely-divided iron as the catalyst. The reaction is reversible. (i) Write the chemical equation for the formation of ammonia via the Haber process. [2] (ii) State the source of either nitrogen or hydrogen. …………….………………………………………………………………….… ……………..………………………………………………...……………….… [1] [Total: 6]

7 6092/Chemistry/2023 Term 3 Weighted Assessment For Examiner’s Use Section C Answer all questions. Write your answers in the spaces provided. 8 Acids in our daily lives Acids are an important part of our everyday lives. Our muscles produce lactic acid, the vinegar we use in our cooking is ethanoic acid, and citric acid is found in the citrus fruits we eat. In addition, the human stomach secretes gastric juice, which contains hydrochloric acid at relatively high concentrations. This strong acid can break down many substances ingested causing them to be absorbed into our blood stream. Although this reaction is important biologically, it has its threats. One example is ‘barium poisoning’ caused by ingesting these metals or their compounds unknowingly. These compounds react with the gastric juices in our stomach producing aqueous barium ions which are highly poisonous. Dissociation of acids pKa (acid dissociation constant ) is the measure of the extent t o which an acid dissociates/ionises. The larger the pKa value, the less dissociation/ionisation of the molecules occurs in solution and thus the weaker the acid. The table below shows the p Ka values of some acids, and the volume of carbon dioxide produced after 1 g of calcium carbonate is reacted with the acid for 1 minute. pKa volume of CO2 produced/cm3 ethanoic acid 4.7 2.32 citric acid 3.1 4.02 lactic acid 3.9 3.62 carbonic acid 6.3 0.95 Table 8.1 (a) High concentrations of aqueous barium ions found in the stomach can cause ‘barium poisoning’ because it will affect the nervous system and could result in paralysis. Yet a ‘barium meal’ containing barium sulfate is often given to patients for consumption before X-ray imaging procedure is carried out. (i) Use ideas about solubility to explain why a ‘barium meal’ is not poisonous and can be fed to patients. ………………………………………………………..…………………..…..… …………………………………………………………..………………....…… [1] (ii) Explain why barium carbonate must not be substituted for barium sulfate in a ‘barium meal’. ………………………………………………………..…………………..…..… …………………………………………………………..………………....…… …………………………………………………………..………………....…… [2]

8 6092/Chemistry/2023 Term 3 Weighted Assessment For Examiner’s Use (b) Describe a test and the results to confirm the identity of carbon dioxide gas. …………………………………………………………………..………………..…… ………………………………………………………………..……………………..… [2] (c) (i) Explain how the ionisation in a weak acid differs from the ionisation of a strong acid, such as dilute hydrochloric acid. …………………………………………………………..………………....…… ………………………………………………………..…………………..…..… …………………………………………………………..………………....…… ………………………………………………………..…………………..…..… [2] (ii) A student commented that pH is similar to pKa in terms of the way their values change in strong or weak acids. Using the information from (c)(i) and the passage above, circle the correct description of pH and pKa in a solution of a strong and weak acid. pH pKa strong acid high / low high / low weak acid high / low high / low [2] (d) Using information from the passage and Table 8.1, suggest which acid is the weakest and explain your reasoning. …………………………………………………………………..………………..…… ………………………………………………………………..……………………..… …………………………………………………………………..………………..…… ………………………………………………………………..……………………..… …………………………………………………………………..………………..…… [3] (e) Litmus papers are commonly used to test for the pH of various substances. Suggest why carbon monoxide has no effect on litmus papers. ………………………………………………………………..……………………..… [1] [Total: 13]

9 6092/Chemistry/2023 Term 3 Weighted Assessment For Examiner’s Use 9 Lavandulol is found in lavender plants. Figure 9.1 shows the formula of a lavandulol molecule. Figure 9.1 Lavandulol can be extracted from lavender flowers using the apparatus shown below. The lavandulol is carried off in small droplets with the steam. (i) What is the name of this separation technique? (ii) Describe the process that takes place in the condenser. Figure 9.2 (a) Using arrows, indicate and