2025 P1 Q021 Q30

2025 A Level H2 Chemistry Paper 1 Suggested Solutions - Q21 to Q30 Question 21 Answer: B Topic: Carboxylic Acid and Derivatives Explanation: For each of the compounds 1 to 3, we hydrolyse the ester with sulfuric acid to form carboxylic acid and alcohol, followed by oxidation of alcohol with dichromate(VI) to form carboxylic acid. If there is only 1 organic compound product then it could be ester J. Ester 1 will form only ethanoic acid on hydrolysis followed by oxidation. Ester 2 will form propanoic acid and propanone as final products. Ester 3 will form butanoic acid and ethanoic acid as final products. --- Question 22 Answer: B Topic: Nitrogen Compounds and Polymers Explanation: The building blocks of proteins are alpha-amino acids where the amine group is bonded to the carbon directly bonded to acid group. Only 2,6-diaminohexanoic acid is alpha-amino acid. The other two are beta-amino acids hence not found in proteins. --- Question 23 Answer: A Topic: Carboxylic Acid and Derivatives Explanation: A is correct. Product formed is ethyl ethanamide. B is wrong. Product formed should be phenyl ethanoate with 2 oxygen atoms instead of 1. C is wrong. Product formed should be 1-methylethyl ethanoate instead of 1-methylethyl propanoate. D is wrong. Product formed should be ethanoic acid instead of ethanal. --- Question 24 Answer: B Topic: Nitrogen Compounds and Polymers Explanation: To compare base strengths between the 3 compounds, we focus on lone pair availability on nitrogen for donation. Phenylamine Y is the least basic since lone pair of N is delocalised into benzene ring and less available for donation. Z is a primary amine with 1 electron donating alkyl group which increase nitrogen's electron density and lone pair availability for donation, hence more basic than Y. X is a secondary amine with 2 electron donating groups therefore should be more basic than Z. Finally the base strength in increasing order should be Y, Z, X. --- Question 25 Answer: C Topic: Organic Chemistry Synthesis Explanation: The synthesis routes with reagents and conditions are given so we just need to verify if the correct final product is formed for each route. Route 2 is wrong since we start off with chloromethylbenzene to form benzoic acid but we want to form phenylethanoic acid (with an additional carbon) instead. Route 3 is wrong since in step 3 there is no reaction between 2 alcohols to form ester. --- Question 26 Answer: C Topic: Electrochemistry Explanation: The chlorine half cell should undergo reduction and silver half cell oxidation and Ecell can be calculated to be +0.56V. On adding sodium chloride to the silver half cell, AgCl ppt is formed which lowers the Ag+ concentration. This shifts the position of equilibrium for silver half cell to the left, and E value should decrease (less than +0.8V). Since silver half cell is the anode, a less positive E for oxidation means Ecell will increase (greater than +0.56V). --- Question 27 Answer: A Topic: Electrochemistry Explanation: From the balanced equation we can deduce 6 moles of electrons are transferred between the reactants. Using formula dG = -nFEcell we can calculate dG to be -625 kJ mol-1. --- Question 28 Answer: C Topic: Electrochemistry Explanation: To be reduced by Ni, the E value for M2+/M half cell must be greater than -0.25V. Therefore answer must be Sn2+. --- Question 29 Answer: B Topic: Electrochemistry Explanation: To find charge of copper ion, we need to determine mole ratio of electrons to Cu. Mole of electrons can be determined via Faraday's equations Q = I.t = n.F Mole of copper is its mass over atomic mass. --- Question 30 Answer: B Topic: Transition Elements Explanation: Element M must be a transition metal with larger atomic mass and smaller radius than Ca. Hence M must have greater density than Ca. MCl2 will have more exothermic lattice energy compared to CaCl2 since M2+ is smaller than Ca2+ and magnitude of lattice energy for MCl2 should be greater. --- This video is brought to you by Singapore's top JC Chemistry tuition centre Chemistry Guru. Subscribe to our channel for more A Level Chemistry video lessons! View the full video with description at my website https://chemistryguru.com.sg/2025-h2c... We are conducting weekly classes for A Level H2 Chem at Bishan, Singapore and online. Find out more at https://chemistryguru.com.sg/