2025 SAJC H1 Chem Prelim P2_Questions

1 ST ANDREW’S JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATIONS HIGHER 1 CANDIDATE NAME CLASS 2 4 S CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 8873/02 02 September 2025 2 hours READ THESE INSTRUCTIONS FIRST Write your name and class on all the work that you hand in. Write in dark blue or black pen. You may use a HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all questions in the spaces provided on the Question Paper. Section B Answer one question. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 26 printed pages (including this cover page). For Examiner’s Use Section A Q1 25 Q2 12 Q3 12 Q4 11 Section B Q5 20 Q6 20 Total 80

2 1 (a) Aluminium oxide , Al2O3, is a white, crystalline solid with high thermal stability and hardness. (i) Complete the electronic configuration of an aluminium atom. 1s2 …………………………………… [1] (ii) Explain why the first ionisation energy of Al is lower than the first ionisation energy of Mg. [2] …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… (iii) Draw the ‘dot-and-cross’ diagram of Al2O3. [1] (iv) The ionic radius of Al3+ is 0.050 nm and Ga3+ is 0.062 nm. Explain the difference in ionic radii between Al3+ and Ga3+. [2] …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… ……………………………………………………………………………………

3 (a) (v) The melting point of Al2O3 is 2072 °C while the melting point of Ga 2O3 is 1720 °C. Explain the difference in melting points of these two oxides. [2] …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… (b) (i) Aluminium oxide , Al2O3 and silicon dioxide , SiO2, are both solid ceramic materials with high melting points and are electrical insulators. Explain how differences in their structure and bonding account for their high melting points and poor electrical conductivity. [3] …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… …………………………………………………………………………………… (ii) Al2O3 and SiO2 have different acid -base behaviour . With the aid of equations, explain the difference in the acid and base behaviour of these two oxides. [4] …………………………………………………………………………………… …………………………………………………………………………………… ……………………………………