2022 A Level H2 Chemistry Paper 1 Solutions - Questions 11 to 20

Question 11 Answer: D Topic: Energetics Explanation: Enthalpy change is negative as given in the question. From the balanced equation, there is an increase in moles of gas, increase in degree of disorder hence entropy change is positive. When delta H is negative and (-T delta S) term is negative, we can deduce Gibbs free energy is always negative and reaction is always feasible or spontaneous. Question 12 Answer: C Topic: Kinetics Explanation: In experiment 2, lead(IV) oxide is added and same mass of it was recovered. There is also an increase in rate of volume of oxygen gas collected. This means PbO2 is a catalyst which lowers the activation energy and increase rate constant in experiment 2. Question 13 Answer: B Topic: Chemical Equilibria Explanation: We can use the ICE table to deduce equilibrium concentrations of reactants and products. Then substitute all these values into equilibrium constant expression to solve for Kc. Question 14 Answer: B Topic: Buffer Solution Explanation: Use buffer equation to calculate [HCO3-]/[H2CO3] = 6266 Then inverse that ratio to find [H2CO3]/[HCO3-] Question 15 Answer: C Topic: Solubility Product Explanation: When aqueous ammonia is added, diamminesilver complex is formed which lowers concentration of Ag+(aq). This will shift position of equilibrium to the right, cause more AgCl salt to dissolve hence solubility will increase. When aqueous sodium chloride is added, concentration of Cl-(aq) increases. This will shift position of equilibrium to the left, less AgCl salt will dissolve and solubility will decrease. Question 16 Answer: C Topic: Solubility Product Explanation: At equilibrium, silver ion concentration is 0.032 moldm-3 and sulfate ion concentration is 0.016 moldm-3. We can then calculate Ksp to be 1.638 x 10e-5 mol3dm-9. In presence of 0.50 moldm-3 of Na2SO4, concentration of Ag+ is 2y, SO42- is approximately 0.50 since contribution of SO42- from sparingly soluble Ag2SO4 is negligible. We can substitute these values into the same Ksp expression to solve for y and then silver ion concentration. Question 17 Answer: A Topic: Organic Chemistry Explanation: Follow the arrow pushing to determine product and deduce which ones are carbocations. Question 18 Answer: C Topic: Intro to Organic Chem Explanation: Optical isomers will react differently with chiral compounds with optical activity. Since only one enantiomer has the desired activity, this means the biological receptors that react with the drug must be chiral. Enantiomers are stereoisomers with almost identical chemical and physical properties. Only difference in physical property is the direction of rotating plane polarised light. Question 19 Answer: B Topic: Intro to Organic Chem Explanation: In the compound alkene is reduced to alkane and alcohol is oxidised to aldehyde. The molecular formula for the reactant and product are the same, they are structural isomers of each other, hence the reaction can be considered isomerisation. Question 20 Answer: D Topic: Intro to Organic Chem Explanation: On reducing all the alkenes to alkanes, we can then find the number of chiral carbons in the product. Subscribe to our channel for more A Level Chemistry video lessons! View the full video with description at my website https://chemistryguru.com.sg/2022-p1-... We are conducting weekly classes for A Level H2 Chem at Bishan, Singapore and online webinar. Find out more at https://chemistryguru.com.sg/ 00:00 Introduction 00:15 Question 11 03:10 Question 12 05:57 Question 13 09:02 Question 14 12:55 Question 15 16:12 Question 16 22:52 Question 17 25:30 Question 18 28:44 Question 19 31:23 Question 20