2024 XMS SEC4 WA1 QP

3 6092/Chemistry/2024 Term 1 Weighted Assessment Section A Answer all questions. Write your answers in the boxes provided at the end of the Section. 1 What is the empirical formula of a gas that contains 50% by mass of sulfur and 50% by mass of oxygen? A SO B SO2 C SO3 D S2O 2 What is the maximum mass of chromium metal, Cr that can be extracted from 76 kg of chromium(III) oxide, Cr2O3? The equation is shown below: 2Cr2O3 → 4Cr + 3O2 A 24 kg B 48 kg C 52 kg D 104 kg 3 Molecules of hydrogen (H 2) and chlorine (C l2) are produced when hydrogen chloride (HC l) decomposes. The equation for the decomposition is shown below. 2HCl(g) → H2(g) + Cl2(g) Hydrogen chloride was added to a container which already contained some hydrogen. After the hydrogen chloride has decomposed for some time, the final volumes of hydrogen chloride, hydrogen and chlorine in the container were determined. The volumes, measured in cm3 at room conditions, before and after the reaction are shown in the table. HCl H2 Cl2 before 200 20 0 after x 100 80 What is the value x? A 0 B 20 C 40 D 160

4 6092/Chemistry/2024 Term 1 Weighted Assessment 4 A solution containing one mole of sodium hydroxide is added to a solution containing one mole of iron(III) sulfate. The equation is shown below: Fe2(SO4)3(aq) + 6NaOH(aq) → 2Fe(OH)3(s) + 3Na2SO4(aq) What is the number of moles of iron(III) hydroxide precipitated? A 3 1 B 2 1 C 6 1 D 3 5 In two experiments to study the rate of reaction between dilute hydrochloric acid and excess zinc powder, the total volume of hydrogen formed was measured at regular time intervals and graphs were plotted from the results. What can be deduced from the graphs? 1 The acid in experiment I was more concentrated than in experiment II. 2 After time t, the reaction in experiment II was still proceeding. 3 The rate of evolution of hydrogen was the same in both experiments at time t. A 1 only B 1 and 2 only C 2 and 3 only D 1, 2 and 3 Question 1 2 3 4 5 Answer total volume of hydrogen / cm3 time /s graph for experiment I graph for experiment II t 0

5 6092/Chemistry/2024 Term 1 Weighted Assessment

5 6092/Chemistry/2024 Term 1 Weighted Assessment For Examiner’s Use Section B Answer all questions. Write your answers in the spaces provided. 6 A student was given a sample of a metal hydroxide of formula, B(OH)2. The student was asked to identify the element B by titrating an aqueous solution of B(OH)2 with 0.095 mol/dm3 nitric acid. A sample of B(OH)2 was placed in a weighed container, which was reweighed. mass of container + B(OH)2 = 10.94 g mass of container = 8.89 g The sample of B(OH)2 was transferred to a flask and made up to 250 cm3 with water. This was solution S. 25.0 cm3 of S was transferred to a conical flask. A few drops of methyl orange indicator were added. Nitric acid was added from a burette until an end-point was reached. Three titrations were done. The diagrams below show parts of the burette with the liquid levels before and after each titration. (a) Use the diagrams to complete the table. titration first second third final reading / cm3 25.80 initial reading / cm3 0.00 volume of acid used / cm3 best results (✓) Using the best results, average volume of acid used = ……………………… cm3 [3]

6 6092/Chemistry/2024 Term 1 Weighted Assessment For Examiner’s Use (b) The equation for the reaction is shown. B(OH)2 + 2HNO3 → B(NO3)2 + 2H2O Calculate the number of moles of the alkali B(OH)2 in 25.0 cm3 of S. [2] (c) Calculate the number of moles of B(OH)2 in the original 250 cm3 of S. [1] (d) Hence find the relative molecular mass, Mr of B(OH)2. [2] (e) Calculate the relative atomic mass, Ar of B, and hence identify element B. Element B is ………………………………. [2] [Total: 10]

7 6092/Chemistry/2024 Term 1 Weighted Assessment For Examiner’s Use 7 (a) Sandstone contains sand (mainly silicon dioxide) and calcium carbonate. 12.00 g of sandstone was added to an excess of dilute hydrochloric acid. CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l) The rate of the reaction was followed by measuring the mass lost during the reaction. Table 8.1 shows the results. Table 8.1 time / min total mass lost / g 0 0.00 2 0.32 4 0.56 6 0.77 8 0.93 10 1.04 12 1.10 14 1.10 16 1.10 (i) How does the data show that the rate of reaction decreased with time? ……………………………………………………………………………………. ……………………………………………………………………………………. [1] (ii) Show by calculations that the percentage by mass of the calcium carbonate in the sandstone is 20.8%.

8 6092/Chemistry/2024 Term 1 Weighted Assessment For Examiner’s Use [3] (b) Four experiments were performed using an equal mass of magnesium metal (an excess) and an acid. For each, the time taken for the reaction to complete was measured. Table 8.2 shows the experimental conditions and the results. Table 8.2 experiment acid used volume of acid in cm3 concentration of acid in mol/dm3 temperature / oC time / min 2 HCl 50 1.00 25 9 3 HCl 100 1.00 35 7 4 H2SO4 50 1.00 35 5 5 H2SO4 100 1.00 35 5 (i) How does the data show that the volume of the acid used does not affect the rate of the reaction? ……………………………………………………………………………………. ……………………………………………………………………………………. [1] (ii) Use ideas about collisions between particles to explain the differences in the reaction rate of the experiments shown in Table 8.2. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. ……………………………………………………………………………………. [4] [Total: 10]

9 6092/Chemistry/2024 Term 1 Weighted Assessment For Examiner’s Use Section C Answer all questions. Write your answers in the spaces provided. 8 Life-Saving Devices Oxygen Generators Rather than carrying heavy high-pressure oxygen cylinders, most aircraft rely on chemically generated oxygen in the event of an emergency. These generators (in the overhead compartments of the aircraft) typically compose of a mixture of sodium chlorate , NaC lO3, iron powder, Fe and barium peroxide, BaO 2. Once initiated, the sodium chlorate undergoes thermal decomposition producing oxygen gas. The iron combines with some of the oxygen to sustain the decomposition process. During the production of oxygen, the generator becomes extremely hot and should not be touched. When a mask is deployed, the flow rate of oxygen gas is designed to change over time as the aircraft descends to a safe altitude. Oxygen supply typically lasts at least 10 minutes. Graph 1 gives information on the typical supply rate from one such oxygen generator. Graph 1 10 seconds after activation, the oxygen supply rate reaches its maximum of 3.6 dm 3 / min. Airbags Timing is everything in an airbag's ability to deploy quickly enough to save a life in a head- on collision. An airbag must be able to deploy in a matter of milliseconds from the initial collision impact. Inside the airbag is a gas generator containing a mi xture of NaN3, KNO3, and SiO2. When the car undergoes a head-on collision, a series of three chemical reactions inside the gas generator produce gas (N2) to fill the airbag and convert NaN3, which is highly toxic, to harmless glass.