Organic Chemistry prac qns

SECONDARY 4 EXPRESS – COMBINED CHEMISTRY Class Index No NAME SCIENCE (CHEMISTRY) Topical Revision – Organic Chemistry Candidates answer on the Question Paper. Additional Materials: Periodic Table, Data Sheet 5086/5088 30 minutes Date: _______________ READ THESE INSTRUCTIONS FIRST Write your class, index number and name on ALL the work you hand in You may use a HB pencil for any drawing. Write in dark blue or black pen. Do not use staples, paper clips, glue or correction fluid. Section A – Multiple Choice Questions (5 marks) There are 15 questions in this Section. Answer ALL questions. For each question, there are four possible answers A, B, C and D . Choose the one you consider correct and write your answer in the given spaces. Each question scores 1 mark. A mark will not be deducted for a wrong answer. Any rough working should be done in this booklet. Section B – Structured Questions (15 marks) Answer ALL questions. The number of marks is given in the brackets [ ] at the end of each question or part question. The total marks for this paper is 20 . FOR EXAMINERS’ USE Target marks Your marks Full Marks TOTAL 20 Adapted from past year prelim papers This document consists of 6 pages.

2 Section A – Multiple Choice Questions (5 marks) Write your answers in the given boxes on page 3. 1 An organic compound, X, decolourises red-brown aqueous bromine and extinguishes a lighted splint with a 'pop' sound when it reacts with magnesium. Which of the following is X? (AES 2024 Q19) A B C D 2 The structure below shows a monomer. Which of the following shows three repeating units of the polymer chain formed? (GMSS 2024 Q19) A B C D © chiasamuel 2025

3 3 Bitumen contains an organic compound with the molecular formula of C ₂₀ H ₄₂ . It undergoes a process called catalytic cracking, to form hydrocarbons with shorter carbon chains which are higher in demand. The chemical equation is given as shown: C ₂₀ H ₄₂ →2C ₆ H ₁₂ + compound K +H ₂ What is the identity of compound K ? (AMKSS 2024 Q17 - edited) A C ₄ H ₈ B C ₄ H ₁₀ C C ₈ H ₁₆ D C ₈ H ₁₈ 4 Many molecules of X combine to form a single molecule Y, as shown in the equation. n X → Y (n is a large number) Which terms best describe X and Y in this reaction? (GESS 2024 Q19) X Y A fraction monomer B monomer fraction C monomer polymer D polymer fraction 5 What reagent is used to differentiate a sample of ethanoic acid from ethanol? A Aqueous bromine B Acidified potassium manganate (VII) C Limewater D Lighted splint WRITE YOUR ANSWERS IN THE GIVEN BOXES BELOW Q1 Q2 Q3 Q4 Q5 © chiasamuel 2025

4 Section B – 15 marks Answer all questions. 6 (a) Naphtha is a fraction of crude oil. Naphtha is processed by cracking in an oil refinery. One of the molecules in naphtha is a saturated hydrocarbon X containing 5 carbon atoms. When this molecule is cracked it produces propane, C ₃ H ₈ and one other hydrocarbon Y. (i) Why is cracking of naphtha an important process in an oil refinery? [2] (ii) Draw a dot-and-cross diagram of propane. [2] (b) Deduce the general formula of the organic compound with a functional formula of –COOH. [1] [Total: 5] © chiasamuel 2025

5 7 In Formula One, octane is used as fuel. Octane belongs to a family of organic compounds called alkanes, which is also known as a hydrocarbon. Table 2.1 shows the melting points and boiling points of a few alkanes. Table 2.1 Name of alkane Formula Melting point / ºC Boiling point / ºC ethane C ₂ H ₆ -183 -89 propane C ₃ H ₈ -188 -42 butane C ₄ H ₁₀ -138 -1 pentane C ₅ H ₁₂ -130 36 hexane C ₆ H ₁₄ -95 69 octane C ₈ H ₁₈ -57 126 (a) What is the type of bonding in octane? [1] (b) Describe why a molecule of octane has a low boiling point. [3] (c) (i) Describe how you would differentiate a sample of octane with a sample of octene. [3] © chiasamuel 2025

6 (ii) Describe how you would differentiate a sample of ethanol with a sample of ethanoic acid. [3] [Total: 10] [END OF PAPER] © chiasamuel 2025