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 2