Cambridge IGCSE Chemistry Pass Exam Papers – 2023 May-June Paper 41

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Answer

Question 1

  1. Sulfur dioxide.

    Explanation:

    Sulfur dioxide (SO₂) is a gas that can dissolve in water to form sulfurous acid, contributing to acid rain formation.

  2. Ammonia.

    Explanation:

    Ammonia (NH₃) dissolves in water to form ammonium hydroxide, which is alkaline.

  3. Xenon.

    Explanation:

    Xenon is a noble gas and is inert, meaning it does not readily react with other elements or compounds.

  4. Oxygen.

    Explanation:

    Oxygen (O₂) is a product of photosynthesis, where plants convert carbon dioxide and water into glucose and oxygen.

  5. Ethene.

    Explanation:

    Ethene (C₂H₄) is an unsaturated hydrocarbon that can undergo polymerization to form polymers such as polyethylene.

  6. Ammonia.

    Explanation:

    In the test for nitrate ions, ammonia (NH₃) is produced as a byproduct when ammonium compounds are reacted with a strong base like sodium hydroxide.

Question 2

  1. 5 protons, 6 neutrons, and 5 electrons.

    Explanation:

    An atom of ¹¹B has 5 protons, 6 neutrons, and 5 electrons.

    1. 20%.

      Explanation:

      The relative abundance of ¹⁰B is calculated based on the average atomic mass and the isotopic masses.

    2. \[ \frac{0.540 \text{g}}{10.8} = 0.05 \text{ mol} \]

      \[ 0.05 \text{ mol} \times 6.02 \times 10^{23} = 3.01 \times 10^{22} \text{ atoms} \]

      Explanation:

      Using the molar mass of boron and Avogadro’s number, the number of atoms in 0.540 g of boron is calculated.

    1. Bauxite.

      Explanation:

      Bauxite is the ore from which aluminum is extracted.

    2. Cryolite.

      Explanation:

      Cryolite lowers the operating temperature and improves conductivity during the extraction of aluminum.

    3. Al³⁺ + 3e⁻ → Al

      Explanation:

      The ionic half-equation for the reduction of aluminum ions at the cathode.

    4. Carbon reacts with oxygen to form carbon dioxide.

      Explanation:

      The carbon anodes react with oxygen formed at the anode to produce carbon dioxide, requiring frequent replacement.

  4. Good conductor of electricity and low density.

    Explanation:

    Aluminum is suitable for overhead electrical cables because it conducts electricity well and has a low density.

  5. Aluminum oxide layer is unreactive.

    Explanation:

    The oxide layer on aluminum prevents it from reacting with other substances, explaining its apparent unreactivity.

    1. 2Al + 3F₂ → 2AlF₃

      Explanation:

      The balanced symbol equation for the reaction between aluminum and fluorine.

    2. Aluminum ion with 8 electrons in the outer shell, fluoride ion with 7 electrons and 1 cross in the outer shell, and charges of 3⁺ on aluminum and 1⁻ on fluoride.

      Explanation:

      The electronic configurations of the aluminum ion and fluoride ion, showing the transfer of electrons and resulting charges.

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