VJC 2023 H2 Chem Yearend Consolidation Practice Paper QP

1 Victoria Junior College 2023 JC1 H2 Chemistry Year-end Practice Paper Recommended Questions For Consolidation of Concepts and Skills Check answers at Cohort Google Drive only after you have attempted the questions. 1 The chalcogens, or the oxygen family, are the elements in group 16 of the Periodic Table. These elements are common in both organic and inorganic compounds. (a) The graph below shows the trend in the first ionisation energies of oxygen, sulfur and selenium. (i) Explain the trend in the first ionisation energies of oxygen, sulfur and selenium. ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… [2] (ii) On the same grid above, sketch the trend in the first ionisation energies of nitrogen, phosphorus and arsenic. [1] (b) A common chalcogen-containing reagent used in both organic and inorganic synthesis is hydrogen peroxide, H2O2. Hydrogen peroxide readily decomposes at room temperature. Iodide ions, I–, catalyse this decomposition, as shown below: Step I: H2O2 + I – → H2O + IO– (slow) Step II: H2O2 + IO– → H2O + O2 + I – The overall equation for the decomposition of hydrogen peroxide is shown below: 2H2O2 → 2H2O + O2

2 The enthalpy and entropy changes for the reaction above are shown in the table below: Enthalpy change / kJ mol–1 –98 Entropy change / J K–1 mol–1 +71 (i) Using the data above, complete the diagram below to show the energy profile diagram for the decomposition of hydrogen peroxide in the presence of iodide ions, labelling clearly the activation energies and enthalpy change of the reaction. [2] (ii) An unknown amount of hydrogen peroxide was allowed to decompose in a 5 dm 3 closed vessel at 120 ºC. When all the hydrogen peroxide was decomposed, a pressure of 177 kPa was measured in the vessel. Determine the amount of hydrogen peroxide that decomposed in the vessel. (Assume that H2O and O2 are ideal gases under the above reaction conditions) [2] 2 (a) Vitamin C is an essential nutrient also known as ascorbic acid. A deficiency of vitamin C leads to a disease known as scurvy. Ascorbic acid is known to have a Mr of 176.0 and contains 40.9% of carbon and 54.5% of oxygen by mass. (i) Determine the molecular formula of ascorbic acid. [2] Energy Progress of reaction H2O2 + I –

3 (b) Ascorbic acid is a monobasic acid, HA, and has a pKa of 4.10. The amount of ascorbic acid contained in dietary supplement tablets can be verified by titration. A tablet containing 500 mg of ascorbic acid was dissolved in 25.0 cm3 of deionised water and titrated against 0.100 mol dm-3 sodium hydroxide. (i) Calculate the volume of 0.100 mol dm -3 sodium hydroxide required for complete neutralisation. [1] (ii) Calculate the initial pH of the ascorbic acid solution. [2] (iii) Suggest a suitable indicator for the titration and describe the colour change at end- point. ……………………………………………………………………………………..………… ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. [1] (iv) With the aid of a suitable equation, explain your choice of indicator in (iii). ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… [2]

4 (c) When a vitamin C tablet is swallowed, it dissolves in the stomach. The pH of the stomach is 2. (i) Determine the percentage of ascorbic acid that is ionised in the stomach. [2] The pH of blood is maintained at 7.35 by a H2CO3/HCO3- buffer. (ii) Using appropriate equations, explain how the buffer minimises changes in pH. ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ………………………………………………………………………………………………. [2] 3 (a) Singapore has been affected by severe smoke haze due to forest fires in the region periodically. The National Environment Agency (NEA) is taking action to ensure that its population is better equipped to deal with haze. During one of the sample analysis of air, the air sample was found to contain elevated amounts of NO2 and gas S. By careful measurements and extrapolation, the value of 𝑝 ρ for gas S has been found to be approximately 110.3, a t 100 °C and at very low pressure. [𝑝 is the pressure of the gas in Pa and ρ is the density of the gas in g m–3] 𝑝 110.3 𝑝 ρ

5 (i) State two main assumptions of the kinetic theory as applied to an ideal gas , and use these to explain why you might expect the behaviour of nitrogen dioxide to be less ideal compared to that of hydrogen. [3] ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… (ii) Calculate an approximate value for the relative molecular mass of S. [1] (iii) Hence, identify gas S, where S is a diatomic neutral pollutant. [1] Gas S is …………………… (b) Atmospheric sulfur dioxide is a major air pollutant that forms acid rain. The pollution problem caused by sulfur dioxide is amplified in the presence of atmospheric oxides of nitrogen, which act as a homogeneous catalyst. Explain, with the aid of equation(s), how atmosphe ric oxides of nitrogen act as a homogeneous catalyst to amplify the pollution problems of sulfur dioxide. [3] ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ……………………………………………………………………………………………… ………………………………………………………………………………………………

6 (c) The Contact Process is an important industrial process that occurs at 450 °C. The key stage in this process is the reaction between sulfur dioxide and oxygen. 2SO2(g) + O2(g) → 2SO3(g) Two laboratory experiments were conducted at 450 °C to investigate the kinetics of this reaction. The graph below shows the results obtained when concentrations of sulfur dioxide were varied. [O2] / mol dm–3 (i) Use the graphs above to deduce the order of reaction with respect to sulfur dioxide and oxygen. [3] 0 0.01 0.02 0.03 0.04 0.05 0.06 0 20 40 60 80 100 120 140 160 Time / s Expt 1 [SO2] =