CXC CSET Chemistry Exam Insights

Sep 23, 2024

CXC CSET Chemistry Paper 2 Breakdown - May/June 2023

General Overview

  • This breakdown is not the official CXC answers but aims to provide a guide for acceptable responses.
  • Focus on understanding the questions and providing complete answers.
  • Allocate time wisely, e.g., no more than 30 minutes on question 1.

Question 1: Data Analysis on Hydrogen Peroxide Decomposition

Part A: Definitions

  • Rate of Reaction: Change in concentration of reactant or product per unit time.
  • Catalyst: A substance that speeds up the rate of a reaction without being chemically changed.

Part B: Recorded Times for Decomposition of Hydrogen Peroxide

  • Record the following times taken for decomposition:
    • Experiment 1: 59 seconds
    • Experiment 2: 42 seconds
    • Experiment 3: 31 seconds
    • Experiment 4: 25 seconds
    • Experiment 5: 21 seconds

Part C: Calculating Rate of Reaction

  • Rate formula: Rate = 1/time (in seconds)
  • Calculated rates:
    • Experiment 1: 0.017
    • Experiment 2: 0.024
    • Experiment 3: 0.032
    • Experiment 4: 0.040
    • Experiment 5: 0.048

Part D: Graph Plotting

  • X-axis: Concentration of hydrogen peroxide (independent variable)
  • Y-axis: Rate of reaction (dependent variable)
  • Plot values and draw a line of best fit.

Part E: Graph Analysis

  • Relationship: As the concentration of hydrogen peroxide increases, the rate of reaction also increases.
  • Concentration at Rate 0.045/s: Approximately 0.256 mole/dm³.

Part F: Mass Calculation

  • Calculate mass using the formula: Mass = Moles × Molar Mass
  • Molar mass of H2O2: 34.01 g/mol
  • Calculated mass: 8.707 grams per dm³.

Part G: Balanced Chemical Equation

  • H2O2 (l) → H2O (l) + O2 (g)

Question 2: States of Matter

Part A: States of Water and Energy of Particles

  • States of matter for water: Solid, Liquid, Gas
  • Energy of Particles:
    • Solid: Little to no kinetic energy, strong forces of attraction.
    • Liquid: Moderate kinetic energy, particles can flow.
    • Gas: Large kinetic energy, weak attractive forces.

Part B: Carbon Dioxide Transition

  • Sublimation Process: Solid CO2 changes directly to gas.
  • Arrangement of Particles: Particles in solid CO2 (dry ice) are closely packed, and upon heating, they gain energy to move apart into the gaseous state.

Part C: Diagrams for Sodium Chloride and Diamond Structures

  • Sodium Chloride: Draw a cubic lattice showing Na+ and Cl- ions.
  • Diamond Structure: Show a tetrahedral structure connecting carbon atoms with covalent bonds.

Question 3: Organic Chemistry

Part A: Compounds Analysis

  • Compound A: Alkane (saturated hydrocarbon)
  • Compound B: Carboxylic acid (C=O, O-H functional group)
  • Compound C: Alcohol (O-H functional group)

Part B: Balanced Equation for Ethanol Burning

  • C2H5OH + O2 → CO2 + H2O
  • Balanced: C2H5OH (l) + 3O2 → 2CO2 + 3H2O (g)

Part C: Solubility Comparison

  • Compound C (Ethanol) is more soluble in water due to its polar OH group.

Part D: Reactivity with Sodium Metal

  • Compound B: More vigorously reacts due to the presence of the carboxylic group, making H more readily lost.

Part E: Reaction Equation with Sodium Metal

  • C2H5OH + 2Na → C2H5O-Na + H2

Part F: Gas Identification Test

  • Test: Lighted splint produces a "pop" sound when hydrogen is present.

Part G: Catalyst in Ester Formation

  • Catalyst Name: Sulfuric acid
  • Compound D Structure: Draw the structure for ethyl propanoate.

Question 4: Oxides and Bonding

Part A: Oxides of Sulfur and Magnesium

  • Oxides of Sulfur: Covalent, low melting point.
  • Oxides of Magnesium: Ionic, high melting point.

Part B: Conductivity

  • Sulfur Oxides: Do not conduct electricity (no ions).
  • Magnesium Oxide: Conducts electricity when molten (ions are free to move).

Question 5: Anaerobic Fermentation

Part A: Fermentation Process

  • Definition: Conversion of glucose to alcohol in the absence of oxygen.
  • High Temperatures Impact: High temperatures denature enzymes in yeast.

Part B: Hydrolysis of Esters

  • Products: Glycerol and corresponding alcohol (e.g., ethanol).

Part C: Saponification Byproduct

  • Byproduct: Glycerol.

Part D: Difference between Soap and Detergent

  • Soap: Forms scum in hard water.
  • Sopless Detergents: Do not form scum.

Question 6: Magnesium Deficiency in Plants

Part A: Importance of Magnesium

  • Key Roles: Part of chlorophyll, aids protein formation, assists in energy transfer.

Part B: Impact of Deficiency

  • Low Yield: Low chlorophyll = Reduced photosynthesis = Less food produced.

Part C: Other Important Metal Ions

  • Calcium: Deficiency leads to stunted growth.
  • Potassium: Deficiency results in weak leaves and poorly developed seeds.