MI_H1_CHEM_P2_Answer

Class Adm No Candidate Name: This question paper consists of X printed pages and X blank page. 2015 Promotional Examination II Pre-university 2 H1 CHEMISTRY 8872 / 02 Paper 2 Structured Questions 16 Sept 2015 2 hours Candidates answer Section A on the Question Paper Additional Materials: Cover page Data Booklet Writing paper READ THESE INSTRUCTIONS FIRST Write your name, index number and class on all the work you hand in. Write in dark blue or black pen on both sides of the writing paper. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluids. The use of an approved scientific calculator is expected, where appropriate. Section A Answer all the questions. Section B Answer two questions on the separate writing papers. Start each new question on a fresh sheet of writing paper. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. FOR EXAMINER’S USE Section A Section B Total Question No 1 (12m) 2 (11m) 3 (7m) 4 (10m) 5 (20m) 6 (20m) 7 (20m) 80 Marks Obtained

2 Section A (40 marks) Answer ALL questions in this section in the spaces provided. 1 Phosphorus is an essential part of life for both human beings and plants. Phosphorus compounds can be found in the minerals in bones and teeth. Phosphorus is also a vital element for plants which is present in the form of phosphates in the fertiliser to maximise the growth of the plant. For Examiner’s Use (a) Phosphoric acid reacts with potassium hydroxide as shown in the following reaction. H3PO4(aq) + 3KOH(aq) → K3PO4(aq) + 3H2O(l) Some thermochemical data are shown below. ΔHθ/ kJ mol-1 Standard enthalpy change of formation of H3PO4(aq) -1277 Standard enthalpy change of formation of KOH(aq) -482 Standard enthalpy change of formation of K3PO4(aq) -1950 Standard enthalpy change of formation of H2O(l) -286 (i) Define standard enthalpy change of formation of H3PO4 (aq). [1] The standard enthalpy change of formation of aqueous H3PO4 is the enthalpy change when one mole of aqueous H3PO4 is formed from its constituent elements in their standard states (H2, P 4 and O2) under standard conditions. (ii) Calculate the standard enthalpy change for the reaction between phosphoric acid and potassium hydroxide based on the information provided. [2] ΔHθ rxn = -1950 + (-286 x 3) – [(-1277) +(-482 x 3)] ; = -85.0 kJ mol-1 ; (b) Phosphorus can react with chlorine to form phosphorus pentachloride and phosphorus trichl