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Chemistry Paper 1: Form 4 QA Model – Document ID 20250302001

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Featured Questions

Here is a list of all the featured questions from the KCSE Mock Chemistry Paper 1:

  1. Using equations only differentiate the bleaching effect of Chlorine and SO2 (2 marks).
  2. The diagram below shows some steps used in the manufacture of sodium carbonate by the Solvay process.
    • (a) Name substance D (1 mark).
    • (b) What process takes place in:
      • i. Step II (2 marks).
      • ii. Step III (2 marks).
    • (c) Write an equation for the reaction taking place in step I (1 mark).
  3. Natural Gallium consists of two isotopes, with atomic masses 69 and 71 in the atomic ratio of 3: 2 respectively. Calculate the relative atomic mass of Gallium (2 marks).
  4. 10 molecules of an unknown gas have a mass of 1.0667 × 10^-21 g. Determine the relative molecular mass of the gas (L=6.0×10^23) (2 marks).
  5. Calcium Hypochlorite is usually added to water when washing.
    • (i) Why is it necessary to add to water (1 mark)?
    • (ii) Give one disadvantage of adding the substance to water when washing (1 mark).
  6. In temperate countries, salt is sprayed on roads to defrost and clear roads but the long-term effect on this practice is costly to motorists.
    • (a) Explain the role of salt in defrosting the ice (1 mark).
    • (b) Explain why the long-term effect is costly to motorists (1 mark).
  7. Describe how you would prepare crystals of sodium nitrate starting with 200 cm³ of 2M sodium hydroxide (3 marks).
  8. 10 cm³ of gaseous hydrocarbon was mixed with 90 cm³ of oxygen and sparked. The resulting volume at r.t.p was 70 cm³ which was reduced by 30 cm³ on shaking with sodium hydroxide. Find the empirical formula of the hydrocarbon (3 marks).
  9. Study the diagram below and answer questions that follow.
    • (a) Identify solid A (1 mark).
    • (b) Give a reason why warm water is used (1 mark).
    • (c) What observation would be made if hydrogen sulfide gas was bubbled into a solution of lead (II) nitrate (1 mark)?
  10. Some average bond energies are given below.
  • Calculate the energy change for the reaction: C2H6 (g) + Cl2 (g) → CH3CH2Cl(g) + HCl(g) (3 marks).
  1. The equation below shows a reversible reaction: H3O+(aq) + HSO4-(aq) ⇌ H2O(l) + H2SO4. Identify the acid in the forward reaction and explain (2 marks).
  2. (a) Define Graham’s gas law (1 mark).
  • (b) Two containers, one with Nitrogen (IV) oxide and the other with bromine simultaneously develop leaks. After 30 minutes, the smell of Nitrogen (VI) oxide is detected. How much longer will it take before bromine is detected? (N = 14, O = 16, Br = 80) (2 marks).
  1. (a) Give one advantage and one disadvantage of nuclear fusion as a source of energy compared to nuclear fission (2 marks).
  • (b) List two applications of radioactivity in agriculture (1 mark).
  • (c) 10g of Chlorine-39 decays to 1.25g in 165 minutes. What is its half-life? (2 marks).
  1. The diagram below shows the industrial manufacture of hydrochloric acid.
  • Name the substances A, B, and C (3 marks).
  1. Study the diagram below and answer the questions given below.
  • (a) Explain why the reaction between ammonia and oxygen in the presence of the catalyst continues without further heating (1 mark).
  • (b) Name catalyst X (1 mark).
  • (c) Write an equation for the reaction which takes place in the flask (1 mark).
  1. Some sodium chloride was found to be contaminated with Copper (II) oxide. Describe how a sample of sodium chloride can be separated from the mixture (2 marks).
  2. Oxygen is obtained on a large scale by the fractional distillation of air.
  • (a) Explain why air is considered a mixture (1 mark).
  • (b) Identify the substance that is removed at the filtration stage (1 mark).
  • (c) Explain why Carbon (IV) oxide and water are removed before liquefaction of air (1 mark).
  • (d) Identify the component that is collected at -186°C (1 mark).
  1. Study the table below and answer the questions that follow:
  • Identify with reasons the substances that:
    • (i) Have a metallic structure (2 marks).
    • (ii) Have a molecular structure (2 marks).
    • (iii) Suggest a reason why substance B has two melting points (1 mark).
    • (iv) Substances A and C conduct electric current in the liquid state. State how the two substances differ as conductors of electric current (2 marks).
  1. Describe how you can distinguish a solution of sodium sulfite from a solution of sodium sulfate in the laboratory (2 marks).
  2. Sodium Hydrogen Carbonate was heated strongly in the laboratory by a student.
  • (a) Write a balanced chemical equation for the above reaction (1 mark).
  • (b) Using an equation, show how sodium carbonate is used to soften hard water (1 mark).
  1. State and explain the observation made when a solution of Hydrochloric acid in methylbenzene is added to Magnesium Carbonate powder (2 marks).
  2. The paper chromatography of a plant extract gave the following results with different solvents:
  • (a) Which is the most suitable solvent for purifying the extract? Explain (2 marks).
  • (b) Ball pen cannot be used to mark the baseline in the above chromatography. Explain (1 mark).
  1. State 2 chemical differences between:
  • (a) Carbon (IV) oxide and Carbon (II) oxide (2 marks).
  • (b) Explain how Carbon (IV) oxide has contributed to the greenhouse effect (2 marks).
  1. Calculate the number of Al3+ ions released when 30 cm³ of 0.1M of Aluminium Sulphate is dissolved in water (L = 6.024 x 10^23) (3 marks).
  2. (a) Give 2 reasons why most laboratory apparatus are made of glass (1 mark).
  • (b) The diagrams below are some common laboratory apparatus. Name each apparatus and state its use (2 marks).
  1. The grid below represents part of the periodic table. Study it and answer the questions that follow:
  • (i) Write the formula of the compound formed when R reacts with oxygen (1 mark).
  • (ii) Write an equation of the reaction taking place when Q and P react (1 mark).
  • (iii) State one use of element T (1 mark).
  1. Draw the structural formula and name possible isomers of organic compounds with the following molecular formula: C3H7Br (2 marks).
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Description

The document is a KCSE Mock Chemistry Paper 1 designed for students preparing for the Kenya Certificate of Secondary Education (KCSE) examinations. It contains a variety of chemistry questions that cover theoretical concepts, practical applications, and problem-solving techniques relevant to the chemistry syllabus in Kenya. Below is a comprehensive overview of the document:

Structure of the Document

  1. Header Information:
    • The document begins with a header section that includes placeholders for the student’s name, class, admission number, index number, signature, and date.
  2. Instructions:
    • Candidates are instructed to write their names and index numbers, answer all questions in the spaces provided, and show all workings clearly where applicable.
    • The paper is allotted a time of 2 hours and has a maximum score of 80 marks.
  3. Question Format:
    • The questions are presented in a structured format, with a mix of theoretical questions, problem-solving exercises, and practical applications.
    • Each question is numbered and includes specific marks allocated, guiding students on the expected depth of their answers.

Content Overview

  1. Chemical Reactions:
    • Questions explore different types of chemical reactions, including the bleaching effect of chlorine and sulfur dioxide, and the Solvay process for sodium carbonate production.
  2. Calculations:
    • Several questions require calculations, including relative atomic mass, molecular mass, and the determination of empirical formulas from experimental data.
  3. Practical Applications:
    • The document includes questions about the practical use of chemicals in various contexts, such as the role of calcium hypochlorite in water purification, and the long-term effects of salt on roads.
  4. Laboratory Techniques:
    • Students are asked to describe laboratory techniques for preparing crystals and separating mixtures, showcasing their understanding of practical chemistry.
  5. Chemical Properties and Behavior:
    • Questions assess understanding of the properties of substances, such as melting points, boiling points, and electrical conductivity, along with the influence of molecular structures.
  6. Environmental Chemistry:
    • Topics related to environmental impact, such as the greenhouse effect of carbon dioxide and the effects of chemical use in agriculture, are included to connect chemistry with real-world issues.
  7. Radioactivity and Nuclear Chemistry:
    • Questions about nuclear fission and fusion, as well as the applications of radioactivity, highlight the importance of these topics in modern chemistry.
  8. Periodic Table and Chemical Bonding:
    • The document tests knowledge on the periodic table, with questions involving the formation of compounds and the nature of chemical bonds.
  9. Chromatography:
    • There are questions related to chromatography techniques and their applications in separating plant extracts, emphasizing analytical chemistry.

Conclusion

The document serves as a comprehensive assessment tool for students, covering a wide range of topics in chemistry. It encourages critical thinking, problem-solving skills, and the application of theoretical knowledge to practical scenarios. The mock exam format prepares students for the KCSE Chemistry Paper by familiarizing them with the types of questions they may encounter in the actual examination.

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