CHEMISTRY
01-10: ACBBBBACBA
11-20: ABBBADBBAB
21-30: CACBDCABCC
31-40: BDBDBBBADA
41-50: DAADBDBADD
COMPLETED
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(1ai)
(i) Pressure: Gas pressure is the force exerted by gas particles on the walls of the container per unit area.
(ii) Volume: The amount of space occupied by a gas is its volume. This can be measured in liters or cubic meters.
(1aii)
The SI unit for pressure is Pascal (Pa).
(1b)
The formation of a sodium ion from a sodium atom is an example of oxidation because the sodium atom loses an electron, resulting in an increase in its oxidation state.
(1c)
Chlorine(I) oxide (Cl₂O) is a molecular compound held together by relatively weak forces such as Van der Waals forces or London dispersion forces. These forces are weaker compared to the strong covalent or ionic bonds found in many other compounds. The weaker intermolecular forces result in a lower melting point for chlorine(I) oxide.
(1d)
(i) Ensure that both the copper(II) oxide and the dilute trioxonitrate(V) acid used in the reaction are of high purity to avoid impurities in the final product.
(ii) Ensure that the reaction is carried out under controlled conditions (e.g., temperature, pressure) to optimize the yield and purity of copper (II) trioxonitrate (V).
(1ei)
- At the cathode (negative electrode): Copper ions (Cu²⁺) in the copper(II) tetraoxosulphate(VI) solution gain electrons and are reduced to solid copper (Cu).
- At the anode (positive electrode): Copper atoms (Cu) from the copper electrode lose electrons and oxidize into copper ions (Cu²⁺), entering the solution.
(1eii)
oxygen gas will be evolved at the anode.
(1f)
Van der Waals forces between chlorine molecules are stronger than those between fluorine molecules because chlorine atoms have more electrons, leading to a larger electron cloud. This larger electron cloud results in stronger temporary dipoles and thus stronger Van der Waals forces.
(1g)
A reversible reaction is a chemical reaction that can proceed in both the forward and reverse directions. It means that the reactants can form products, and the products can also react to form the original reactants.
(1h)
In chemistry, a postulate refers to a fundamental assumption or hypothesis that forms the basis for a theory or model. Postulates are statements accepted without direct proof but are used to derive and explain other principles or observations. They serve as starting points for building theoretical frameworks that help understand and predict chemical behavior.
(1i)
An atom of sodium has 6.02×10²³ molecules equivalent to 1 mole
No. of moles = mass/molar mass
Mass= no. of moles × molar mass
= 1 × 23
Mass = 23g
(1hi)
Graham's law states that the rate of effusion or diffusion of a gas is inversely proportional to the square root of its molar mass.
(1hii)
The melting point of a sample of a compound is related to its purity in the sense that impurities tend to lower and broaden the melting point range. A pure substance has a sharp and well-defined melting point, while impurities introduce variability and may cause the substance to melt over a range of temperatures. Therefore, a higher degree of impurity is often associated with a lower and less sharp melting point. Melting point determination is a common method used to assess the purity of a substance
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(4ai)
Air is a mixture of gases that primarily consists of nitrogen (about 78%), oxygen (about 21%), argon (about 0.93%), carbon dioxide, and trace amounts of other gases, as well as varying amounts of water vapor.
(4aii)
Nitrogen
(4aiii)
A noble gas is a group of elements in the periodic table that includes helium, neon, argon, krypton, xenon
(4aiv)
(i) Noble gases are generally chemically inert, meaning they do not readily form compounds with other elements.
(ii) They have a stable electron configuration, with a full outer shell of electrons.
(iii) Noble gases are colorless and odorless in their elemental form.
(4bi)
(i) Calcium chloride (CaCl2)
(ii) Silica gel
(4bii)
N₂(g) +3H₂(g) ---> 2NH₃(g)
(4biii)
Downward displacement of water method.
(4biv)
Different gases may have different physical and chemical properties, affecting their behavior during collection. For example, some gases may be soluble in water, reactive with certain materials, or have different densities, which would necessitate specific collection methods to ensure accurate and safe results.
(4ci)
- Haematite (Fe2O3): Undergoes reduction to produce iron. The iron oxide is reduced to iron in the presence of carbon monoxide.
- Coke (Carbon): Provides the carbon necessary for the reduction of iron ore and acts as a source of heat.
- Limestone (CaCO3): Undergoes thermal decomposition to produce calcium oxide, which reacts with impurities (silica) to form a slag.
(4cii)
Cast iron is a brittle alloy of iron and carbon, while wrought iron is a more malleable form of iron with a lower carbon content and fibrous structure.
(4ciii)
- Lower Temperature: The reaction is exothermic, so lower temperatures favor the exothermic direction.
- Higher Pressure: Increasing pressure can favor the side with fewer moles of gas (assuming a change in the number of moles).
(4di)
Both diamond and graphite have high melting points because they are made up of carbon atoms bonded together by strong covalent bonds. These bonds require a lot of energy to break, resulting in high melting points for both substances.
(4dii)
I. The copper metal would undergo a reaction with silver trioxonitrate (V) because copper is more reactive than silver and can displace silver from its salt.
II. The visible change would be the deposition of silver metal from the solution as copper displaces silver from the silver trioxonitrate (V) solution. Copper (Cu) would go into the solution as copper ions (Cu2+), and silver metal would be deposited.
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(5a)
Soap is manufactured through a process called saponification. In this process, pellets of sodium hydroxide (NaOH) and vegetable oil are used as the main ingredients. First, the vegetable oil is heated, and then the heated vegetable oil is mixed with sodium hydroxide pellets. This mixture is stirred continuously until a thick, creamy consistency is achieved. This mixture is then left to cool and solidify into soap bars. The sodium hydroxide reacts with the fatty acids present in the vegetable oil, resulting in the formation of soap molecules.
(5bi)
The industrial preparation of oxygen from air involves a process called fractional distillation. Air is first compressed and cooled, causing it to liquefy. This liquefied air is then subjected to fractional distillation, a process that separates the different components of air based on their boiling points. Oxygen, which has a lower boiling point than nitrogen, is separated and collected as a pure gas.
(5bii)
(i) oxygen: Oxygen supports combustion and is necessary for a flame to burn.
(ii) Hydrogen: hydrogen is highly flammable and can readily ignite.
(5ci)
(i) Calcium hydroxide: It helps to neutralize any acidic components and improve the overall quality of the water.
(ii) Calcium: is an essential nutrient for human health and is important for the development and maintenance of strong bones and teeth.
(5cii)
(i) Natural sources
(ii) Fossil fuel extraction and combustion
(5ciii)
When sulfur reacts with iron, iron sulfide (FeS) is formed. This reaction can be represented by the equation:
Fe + S -> FeS
(5di)
The term hardness of water refers to the concentrationof dissolved minerals, particularly calcium and magnesium ions. Hard water can cause build-up and scaling in pipes and appliances, reduce the effectiveness of soaps and detergents, and can also affect the taste and odor of water.
(5dii)
2H2SO4 + 2NaCl → 2HCl + Na2SO4
(5diii)
Fe2O3 + 3CO → 2Fe + 3CO2
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May 18, 2023, 11:16:43 am
