2024 Prelims SAJC H2 Chem P1 (Ans)

1 ST ANDREW’S JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATIONS HIGHER 2 CANDIDATE NAME CLASS 2 3 S CHEMISTRY Paper 1 Multiple Choice Candidate answer on the Optical Answer Sheet Additional Materials: Data Booklet 9729/01 11 September 2024 1 hour READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, glue or correction fluid. There are thirty questions on this paper. Answer all questions. For each question there are four possible answers A, B, C and D. Choose the one you consider correct and record your choice in soft pencil on the separate Optical Answer Sheet. Each correct answer will score one mark. A mark will not be deducted for a wrong answer. Any rough working should be done in this booklet. The use of an approved scientific calculator is expected, where appropriate. This document consists of XX printed pages (including this cover page).

2 1 Use of Data Booklet is relevant to this question. Sodium azide, NaN3, is an ionic salt which is used to inflate airbags inside a car during a crash. How many electrons are there in a sodium ion and an azide ion respectively? sodium ion azide ion A 10 22 B 11 21 C 22 42 D 22 43 Ans: A Total number of electrons in Na+ = 11 – 1 = 10 Total number of electrons in N3– = (7 x 3) + 1 = 22 2 The first seven successive ionisation energies for element Y are as shown. Y is found in Period 3. 1st 2nd 3rd 4th 5th 6th 7th Ionisation energy / kJ mol–1 1010 1900 2900 5000 6300 21300 25400 Which statements are correct? 1 The valence shell of Y contains only s and p orbitals. 2 The element after Y in the same period has a lower first ionisation energy than Y. 3 Y can react with magnesium metal to form the compound Mg3Y2. A 1, 2 and 3 B 1 and 3 only C 2 and 3 only D 2 only Ans: C Option 1 is wrong as the valence shell is n = 3, which consists of s, p and d orbitals. The d orbitals are empty though.

3 Option 2 is correct as the valence electronic configuration of the element after Y is 3s23p4, where there is interelectronic repulsion between the paired electrons and this outweighs the increase in nuclear charge across the period. Hence, the 1 st ionisation energy will be lower than that of Y. Option 3 is correct as Y is P which has a valency of 3. Mg has a valency of 2. 3 The structure of ice is as shown. Which statement is incorrect? A The open structure causes ice to be less dense than liquid water. B The open structure gives ice a smaller mass than liquid water. C Four electrons from each oxygen are involved in forming hydrogen bonds. D Each oxygen atom in a water molecule is tetrahedrally bonded to 4 hydrogen atoms. Ans: B Option A is correct as the open structure (owing to the hydrogen bonds between water molecules) results in a larger volume occupied than liquid water and hence, density of ice is smaller than water. Option B is incorrect as th