WAEC SSCE - Chemistry - 2012

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An atom consists of electrons that occupy specific energy levels or shells around the nucleus. These shells are further divided into sub-levels. There are four types of sub-levels: s, p, d, and f. Each sub-level has a specific number of orbitals, which are regions of space where electrons are most likely to be found. The p-sub level has three orbitals. These orbitals are designated as px, py, and pz, each of which can hold a maximum of two electrons. Therefore, the p-sub level can hold a total of six electrons, which are distributed among the three orbitals. In summary, the number of orbitals in a p-sub level of an atom is three, and the correct option is (B) 3.

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The substance mainly responsible for the depletion of the ozone layer is Chlorofluorocarbon or CFC. CFCs are a type of synthetic chemical compound that is commonly used in refrigerants, air conditioning systems, and aerosol sprays. When CFCs are released into the atmosphere, they rise up to the ozone layer and react with the ozone molecules. This chemical reaction breaks down the ozone molecules, resulting in the depletion of the ozone layer. The ozone layer is an essential layer in the Earth's atmosphere that protects us from harmful ultraviolet (UV) radiation from the sun. A decrease in the ozone layer could lead to an increase in skin cancer and other negative effects on human and animal health.

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Fermentation is a process by which microorganisms such as yeast convert sugars into alcohol, such as ethanol. The process occurs under anaerobic conditions, meaning in the absence of oxygen. The microorganisms break down the sugar molecules into ethanol and carbon dioxide. Out of the given options, vinegar would not produce ethanol when fermented because vinegar is a diluted solution of acetic acid, not a sugar. It is produced by the fermentation of ethanol by acetic acid bacteria, which convert the ethanol into acetic acid. On the other hand, cane sugar, glucose, and starch are all sources of fermentable sugars and can be used to produce ethanol when fermented. Therefore, the correct option is (D) Vinegar.

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The correct answer is "number of valence electrons". Elements in the same group on the periodic table have similar chemical and physical properties because they have the same number of valence electrons, which are the electrons in the outermost energy level of an atom. Valence electrons are important because they are involved in chemical bonding, which determines the reactivity and behavior of elements. Therefore, elements in the same group have similar chemical reactivity and tend to form similar types of chemical bonds.

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A metalloid is an element that has properties of both metals and nonmetals. These elements are also called semimetals. Out of the options listed, only Silicon is a metalloid. Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and it is a member of the group 14 of the periodic table. Carbon, oxygen, and sodium are not metalloids. Carbon and oxygen are nonmetals, while sodium is a metal. In summary, Silicon is a metalloid because it has properties of both metals and nonmetals, while carbon, oxygen, and sodium are not metalloids because they do not have properties of both metals and nonmetals.

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Both the dry cell and car battery function on redox reactions, which involve the transfer of electrons between reactants. A dry cell contains an electrolyte paste that allows for the transfer of electrons between the zinc outer casing (anode) and the carbon rod (cathode) in the center of the cell. The zinc atoms lose electrons and become positively charged ions, while the carbon atoms gain those electrons and become negatively charged ions. This transfer of electrons creates an electric current that can power devices like flashlights. Similarly, a car battery uses a redox reaction to generate electricity. The battery contains two electrodes - a lead dioxide cathode and a lead anode - that are immersed in an electrolyte solution of sulfuric acid. When the battery is connected to a circuit, the lead dioxide electrode accepts electrons from the lead anode, creating a flow of electricity. An electric generator, on the other hand, does not rely on a redox reaction to function. Instead, it works by converting mechanical energy into electrical energy. The generator contains a wire coil that rotates within a magnetic field, creating an electric current in the wire. Therefore, the devices that function on redox reactions are l and ll only, and the answer is option C - l and ll only.

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Brass is a metal alloy made by combining two main elements, copper (Cu) and zinc (Zn), in varying proportions. The exact proportions of copper and zinc can vary depending on the desired properties of the brass, such as its color, hardness, and durability. Other elements, such as lead (Pb), tin (Sn), or magnesium (Mg), can also be added to brass to enhance certain characteristics. However, they are not considered the main components of brass, which is always a mixture of copper and zinc. So, the correct answer is "Cu and Zn".

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The metal that would readily displace hydrogen from steam is Magnesium. This is because Magnesium is a highly reactive metal that easily reacts with water vapor (steam) to produce magnesium oxide and hydrogen gas. The reaction is as follows: Mg (s) + H2O (g) → MgO (s) + H2 (g) The other metals listed, copper, lead, and silver, are less reactive and would not readily displace hydrogen from steam. Copper and silver are relatively stable and do not react with water or steam, while lead may react slowly but not as vigorously as magnesium.

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Nuclear wastes are not usually recycled. Unlike other types of wastes such as aluminium cans, glass bottles, and paper wastes which can be recycled, nuclear wastes are highly radioactive and pose a significant threat to human health and the environment. Therefore, nuclear wastes are typically stored in special facilities designed to prevent their escape into the environment, rather than being recycled or reused.

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The factor that will not affect the rate of the reaction is the pressure of the reaction system. The given chemical equation does not involve any gaseous reactants or products, so the pressure of the reaction system will not have any effect on the rate of the reaction. The other factors such as particle size of CuO, concentration of H\(_2\)SO\(_4(aq)\), and temperature of the reacting mixture can all affect the rate of the reaction. - The smaller the particle size of CuO, the larger the surface area, which leads to an increase in the frequency of collisions between reactant particles and hence an increase in the rate of the reaction. - The higher the concentration of H\(_2\)SO\(_4(aq)\), the more the number of H\(_2\)SO\(_4(aq)\) molecules available for reaction with CuO, which leads to an increase in the frequency of collisions and hence an increase in the rate of the reaction. - The higher the temperature of the reacting mixture, the higher the kinetic energy of the reactant molecules, which leads to an increase in the frequency of collisions and hence an increase in the rate of the reaction.

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The reaction of a substance with NH\(_4\)NO\(_{3(aq)}\) to generate ammonia gas is a test for identifying substances that are basic in nature. The reaction is known as the "Ammonia Test". NH\(_4\)NO\(_{3(aq)}\) is an acidic solution and it reacts with basic substances to produce ammonia gas. Among the given options, only NaOH is a strong base that can react with NH\(_4\)NO\(_{3(aq)}\) to generate ammonia gas. Therefore, the substance L is likely to be NaOH.

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To determine the number of sulfur atoms in 3.20g of SO\(_{2(g)}\), we first need to find the number of moles of SO\(_{2(g)}\) present in the given mass. This can be done using the molecular weight of SO\(_{2(g)}\), which is calculated by adding the atomic weights of sulfur and oxygen in the molecule: Molecular weight of SO\(_{2(g)}\) = (1 × atomic weight of S) + (2 × atomic weight of O) = (1 × 32.0) + (2 × 16.0) = 64.0 g/mol Next, we can calculate the number of moles of SO\(_{2(g)}\) present in 3.20g using the formula: Number of moles = Given mass ÷ Molecular weight Number of moles of SO\(_{2(g)}\) = 3.20 g ÷ 64.0 g/mol = 0.05 mol Finally, we can use Avogadro's constant to calculate the number of sulfur atoms present in 0.05 mol of SO\(_{2(g)}\): Number of sulfur atoms = Number of moles of SO\(_{2(g)}\) × Avogadro's constant × Number of sulfur atoms per molecule From the balanced chemical equation for the combustion of sulfur dioxide, we know that each molecule of SO\(_{2(g)}\) contains one atom of sulfur. Therefore, the number of sulfur atoms per molecule of SO\(_{2(g)}\) is 1. Number of sulfur atoms = 0.05 mol × 6.02 x 10\(^{23}\) mol\(^{-1}\) × 1 = 3.01 x 10\(^{22}\) Therefore, the number of sulfur atoms in 3.20g of SO\(_{2(g)}\) is 3.01 x 10\(^{22}\), and the correct option is (A) 3.01 x 10\(^{22}\).

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The pH scale measures the acidity or basicity of a solution, with a pH of 7 being neutral, pH values below 7 being acidic, and pH values above 7 being basic (alkaline). Out of the options listed, pH value of 13 indicates that a solution is a strong base. A strong base is a substance that completely dissociates in water to produce hydroxide ions (OH\(^-\)) and has a pH greater than 7. A pH of 13 is highly alkaline, which indicates that the solution has a high concentration of hydroxide ions. In summary, a pH value of 13 indicates that a solution is a strong base because it is highly alkaline and has a high concentration of hydroxide ions.

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The gas with the lowest rate of diffusion under the given conditions is the gas that is the heaviest, which means it has the highest molar mass. The molar masses of the gases listed in the question are: H₂ (2.0 g/mol), He (4.0 g/mol), O₂ (32.0 g/mol), and CI₂ (71.0 g/mol). Therefore, the gas with the lowest rate of diffusion is CI₂, because it has the highest molar mass. This means that CI₂ molecules are larger and heavier than molecules of the other gases listed, and so they move more slowly and take longer to diffuse through a medium. In summary, the heavier the gas, the slower it diffuses, and the lighter the gas, the faster it diffuses.

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To solve this problem, we need to use stoichiometry to relate the amount of CaCO\(_3\) reacted to the amount of CaCl\(_2\) produced. First, we need to balance the equation to make sure that the number of atoms of each element is equal on both sides: CaCO\(_3\) + 2HCl → CaCl\(_2\) + H\(_2\)O + CO\(_2\) Next, we need to determine the mole ratio between CaCO\(_3\) and CaCl\(_2\) from the balanced equation: 1 mole CaCO\(_3\) : 1 mole CaCl\(_2\) Now, we can use this mole ratio to calculate the number of moles of CaCl\(_2\) produced from 25.0g of CaCO\(_3\): 25.0 g CaCO\(_3\) x (1 mole CaCO\(_3\)/100 g CaCO\(_3\)) x (1 mole CaCl\(_2\)/1 mole CaCO\(_3\)) = 0.250 mole CaCl\(_2\) Finally, we can use the molar mass of CaCl\(_2\) to calculate the mass produced: 0.250 mole CaCl\(_2\) x 111 g CaCl\(_2\)/1 mole CaCl\(_2\) = 27.8 g CaCl\(_2\) Therefore, the mass of CaCl\(_2\) produced when 25.0g of CaCO\(_3\) is reacted with excess HCl\(_{(aq)}\) is 27.8 g. The correct answer is.

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When magnesium burns in air, it undergoes a chemical reaction with oxygen to form magnesium oxide. This reaction is highly exothermic, which means it releases a significant amount of energy in the form of heat and light. The heat energy is produced as a result of the exothermic reaction between magnesium and oxygen. This energy is released into the surroundings, which causes the temperature of the surroundings to increase. The amount of heat produced depends on the quantity of magnesium burned and the conditions under which the reaction occurs. The light energy is produced due to the high temperature of the reaction, which causes the magnesium and magnesium oxide to emit light in the form of a bright white flame. The intensity and color of the light depend on the temperature of the reaction and the composition of the materials involved. Therefore, the energy evolved when magnesium burns in air is in the form of light and heat, and the correct option is (C) light and heat.

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The ion with an electron configuration different from the others is ₁₇CI^-. Chlorine (CI) has the electron configuration of 1s²2s²2p⁶3s²3p⁵ when neutral, but when it gains an electron to become an ion, it gains one more electron in the 3p subshell to have a full outer shell of 8 electrons, which gives it the electron configuration of 1s²2s²2p⁶3s²3p⁶. Oxygen (O), magnesium (Mg), and aluminum (AI) have electron configurations of 1s²2s²2p⁴, 1s²2s²2p⁶3s², and 1s²2s²2p⁶3s²3p¹, respectively, when neutral. When they become ions, they either lose or gain electrons to achieve a full outer shell of 8 electrons for stability, which does not change their electron configuration in the same shell. Therefore, the correct answer is ₁₇CI^-.

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Bromine is the halogen that is liquid at room temperature. This is because it has the lowest boiling point of all the halogens, meaning it can easily evaporate to become a gas at higher temperatures. At room temperature, which is typically around 20-25 degrees Celsius (68-77 degrees Fahrenheit), bromine remains in its liquid state because its boiling point is 59 degrees Celsius (138 degrees Fahrenheit). Chlorine and fluorine are gases at room temperature because they have much lower boiling points than bromine. Iodine is a solid at room temperature, as it has a higher boiling point than bromine and therefore requires higher temperatures to turn into a liquid.

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The process represented by the given chemical equation is cracking. Cracking is a chemical process that involves breaking down larger hydrocarbon molecules into smaller ones. In this reaction, a long-chain hydrocarbon molecule (C16H34) is broken down into two smaller hydrocarbon molecules (C5H12 and C11H22) by the application of heat, which causes the bonds between the atoms in the hydrocarbon to break. Cracking is an important process in the petroleum industry because it allows for the production of smaller hydrocarbons that are more useful as fuels and other industrial applications.

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In the compound [Fe(CN)\(_6\)]\(^{3-}\), the overall charge of the compound is negative 3 (\(^{3-}\)), which means the sum of the oxidation states of all the atoms in the compound must equal negative 3. We can start by looking at the cyanide ion (CN\(^-\)), which has a known oxidation state of negative 1 (\(-1\)). There are six of them in the compound, giving a total charge of negative 6 (\(-1 \times 6 = -6\)). To find the oxidation state of iron (Fe), we can use the fact that the sum of the oxidation states of all the atoms in a compound is equal to the overall charge of the compound. Let x be the oxidation state of iron (Fe). Therefore, x + (-6) = -3 Solving for x, we get: x = +3 Therefore, the oxidation state of iron (Fe) in [Fe(CN)\(_6\)]\(^{3-}\) is +3.

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The industrial process that depends on the action of enzymes is the brewing of beer. Enzymes are proteins that act as catalysts, which means they speed up chemical reactions without being consumed in the process. In the brewing process, enzymes break down complex sugars in grains like barley into simpler sugars like glucose, which can then be fermented by yeast to produce alcohol and carbon dioxide. This process is called mashing and it relies on the action of enzymes naturally present in the grains, or added to the mash in the form of malted barley. So, enzymes play a crucial role in converting the complex carbohydrates in grains into the simple sugars needed to produce beer.

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The correct statement(s) about a radioactive substance is/are l and lll only. Radioactive substances emit radiation continuously and spontaneously. The emitted radiations are not affected by temperature and pressure, hence statement ll is incorrect. Radiation can penetrate opaque matter, which is why it is important to handle radioactive substances with caution and protective gear. Therefore, statement lll is correct.

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The molecular formula of the compound is C\(_4\)H\(_{10}\)O, which means it has four carbon atoms, ten hydrogen atoms, and one oxygen atom. Since it is a tertiary alkanol, it has a hydroxyl group (-OH) attached to a tertiary carbon atom, which means that the carbon atom is bonded to three other carbon atoms. Option (C) has the correct number of carbon atoms and a tertiary carbon atom attached to the hydroxyl group, which makes it a plausible option. The structural formula for (C) is (CH₃)₃COH, which represents a tertiary butanol. Therefore, option (C) is the correct answer.

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When a substance changes directly from the solid state to the gaseous state without forming a liquid, the process is called sublimation. This means that the solid substance goes through a phase change and turns into gas without passing through the liquid phase. The term "sublime" is used to describe this process. For example, dry ice, which is solid carbon dioxide, undergoes sublimation when it is exposed to room temperature or higher temperatures, and turns directly into carbon dioxide gas without forming a liquid. Similarly, iodine crystals, which are solids, can sublime when heated, forming purple vapors of iodine gas.

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The metal that is commonly used in the production of both paints and overhead electric cables is aluminum. Aluminum is a lightweight and durable metal that is resistant to corrosion and can conduct electricity efficiently. It is also easy to shape and mold, which makes it a versatile material for various industrial applications. In the production of paints, aluminum is used as a pigment to provide a metallic or reflective finish. In the case of overhead electric cables, aluminum is preferred because it is lightweight, strong, and can conduct electricity effectively.

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MgO does not readily dissolve in water because its lattice energy is higher than its hydration energy. MgO is an ionic compound that has a strong ionic bond between magnesium and oxygen. When it is placed in water, the water molecules surround the ions and try to separate them from each other. This process is known as hydration, and it releases energy. However, the energy required to break the ionic bond in MgO is greater than the energy released during hydration. Therefore, MgO does not dissolve easily in water.

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The vapour pressure of a liquid is the pressure exerted by the molecules of the liquid when they evaporate and become a gas. The higher the temperature, the more energy the liquid molecules have, which means they move faster and are more likely to escape into the gas phase. So, option l is correct, as the vapour pressure of a liquid depends on the temperature. Rate of condensation refers to the process by which gas molecules collide and stick together to form a liquid. However, this process does not affect the vapour pressure of the liquid, as it is only the reverse of the process of evaporation. Therefore, option ll is not correct. Cohesive forces are the forces that hold the particles of a liquid together. The stronger these forces, the harder it is for the molecules to escape into the gas phase, and thus the lower the vapour pressure of the liquid. So, option lll is correct, as the vapour pressure of a liquid depends on the cohesive forces holding the particles together. In conclusion, the correct option is l and lll only. The vapour pressure of a liquid depends on the temperature and the cohesive forces holding the particles together.

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Metals usually have atomic radii greater than their ionic radii. This is because when a metal atom loses one or more electrons to form a cation, the effective nuclear charge (positive charge of the nucleus) increases, pulling the remaining electrons closer to the nucleus and reducing the size of the ion. However, in the metallic state, the outermost electrons are delocalized, meaning they are not associated with any one particular nucleus, but rather are free to move throughout the metal lattice. This results in the metallic radius being larger than the ionic radius.

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The formula of a compound gives the type and number of atoms that are present in a molecule of that compound. To determine the formula of mercury (l) dioxonitrate (III), we need to determine the oxidation states of the atoms present in the compound. The symbol Hg represents the element mercury, which has a valence of +1 in this compound. The symbol NO\(_2\) represents the nitrite ion, which has a valence of -1. The Roman numeral III indicates that the compound contains three nitrite ions. To balance the charges of the mercury ion and the nitrite ions, we need two nitrite ions for every mercury ion. This gives us the formula Hg\(_2\)(NO\(_2\))\(_2\), and the correct option is (C) Hg\(_2\)(NO\(_2\))\(_2\).

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The electron configuration of an atom in its ground state is the arrangement of electrons in the lowest possible energy levels. The configuration that represents the ground state will have all the electrons in their respective orbitals according to the Aufbau principle, Pauli exclusion principle, and Hund's rule. Now, looking at the options: - has a partially filled p orbital, which is not allowed for an atom in its ground state. - also has a partially filled p orbital, which is again not allowed for an atom in its ground state. - has three electrons in the p sublevel, which violates the Pauli exclusion principle. - has all the electrons in their respective orbitals according to the Aufbau principle, Pauli exclusion principle, and Hund's rule. Thus, represents the electron configuration of an atom in its ground state. Therefore, the correct option is the one that shows the electron configuration with all the electrons in their respective orbitals according to the Aufbau principle, Pauli exclusion principle, and Hund's rule. In this case, it is: 1s²2s²2p⁶3s⁰.

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The correct answer is that the d-block elements are paramagnetic because they contain unpaired electrons in the partially filled 3d-orbital. Paramagnetism refers to the tendency of a substance to become magnetized when placed in an external magnetic field. This occurs because unpaired electrons in the d-orbitals of these elements are attracted to the magnetic field and align themselves with it, causing the substance as a whole to become magnetized. Therefore, the presence of unpaired electrons in the d-orbitals of these elements is responsible for their paramagnetic behavior.

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The chemical equation represents the combustion of methanol (CH\(_3\)OH) in the presence of oxygen (O\(_2\)). The reactants, methanol and oxygen, combine to produce carbon dioxide (CO\(_2\)) and water (H\(_2\)O). The balanced chemical equation for this reaction is: 2CH\(_3\)OH + 3O\(_2\) → 2CO\(_2\) + 4H\(_2\)O From this equation, we can see that the values of x, y, and z respectively are 2, 3, and 4. Therefore, the correct option is (A) 2, 3, and 4.

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When two elements with a large electronegativity difference combine, one element attracts electrons more strongly than the other, causing the electrons to be shared unequally. In such a case, the electron pair is pulled closer to the more electronegative element, resulting in partial charges on the atoms. This type of bonding is called polar covalent bonding, where there is a difference in electronegativity between the two atoms. However, if the electronegativity difference between the two elements is very large, one element will transfer its electrons completely to the other element to form ions. In this case, ionic bonding occurs, where there is a complete transfer of electrons from one element to another to form positively and negatively charged ions. Therefore, when two elements with a large electronegativity difference combine, the resulting compound is likely to be ionic in nature. Hence, the correct option is ionic.

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The shape of a graphite crystal is hexagonal. Graphite is made up of layers of carbon atoms arranged in a hexagonal lattice structure. Each carbon atom is bonded to three other carbon atoms in a flat plane, forming a hexagonal pattern. The layers are stacked on top of each other, held together by weak intermolecular forces, allowing the layers to slide past each other, making graphite a good lubricant.

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H\(_2\)O is a liquid at ordinary temperature because it has strong hydrogen bonds holding its molecules together. Hydrogen bonds are the intermolecular forces of attraction between the hydrogen atoms of one molecule and the oxygen atom of another molecule. These hydrogen bonds are relatively strong compared to other intermolecular forces like induced dipole-induced dipole forces or ionic forces. On the other hand, H\(_2\)S is a gas at ordinary temperature because it has weak intermolecular forces holding its molecules together. Thus, the correct option is "strong hydrogen bonds holding its molecules together".

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The complex compound formed when aluminum dissolves in aqueous sodium hydroxide is NaAl(OH)₄. This is because when aluminum reacts with sodium hydroxide, it forms a complex ion [Al(OH)₄]^-. This complex ion has a negative charge and combines with a positive ion like Na⁺ to form the final compound NaAl(OH)₄. The other options are not correct because they do not represent the correct combination of aluminum and sodium hydroxide.

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(a) (i) Structural isomers are compounds that have the same molecular formula but different structural formulae, that is, their atoms are connected or arranged differently.

(a) (ii) The four structural isomeric alkanols of molecular formula \(\mathrm{C_4H_{10}O}\) are shown below.

(a) (iii) 2-Methylpropan-2-ol, \(\mathrm{(CH_3)_3COH}\), does not react easily with acidified potassium dichromate(VI) on heating because it is a tertiary alkanol.

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(b) (i) In the presence of ultraviolet light, chlorine substitutes a hydrogen atom in pentane:

\[\mathrm{C_5H_{12} + Cl_2 \xrightarrow{h\nu} C_5H_{11}Cl + HCl}\]

The hydrogen chloride gas formed fumes in moist air.

(b) (ii) The major monochlorination product is 2-chloropentane.

(b) (iii) Light supplies the energy for the homolytic breaking of the \(\mathrm{Cl-Cl}\) bond to form chlorine radicals. It therefore initiates the free-radical substitution reaction.

(b) (iv) Pentane distils off first. It has a lower molar mass, \(72\), and weaker intermolecular forces than chloropentane, \(\mathrm{C_5H_{11}Cl}\), of molar mass \(106.5\). Therefore, pentane has the lower boiling point.

(b) (v) The main product formed from but-1-ene is 1,2-dichlorobutane:

\[\mathrm{CH_2{=}CHCH_2CH_3 + Cl_2 \longrightarrow CH_2ClCHClCH_2CH_3}\]

Its molecular formula is \(\mathrm{C_4H_8Cl_2}\).

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(c) Products of hydration

(i) \(\mathrm{CH_3CH(CH_3)CH{=}CH_2}\) gives 3-methylbutan-2-ol:

\[\mathrm{CH_3CH(CH_3)CH(OH)CH_3}\]

(ii) \(\mathrm{CH_2{=}CHCOOH}\) gives 2-hydroxypropanoic acid:

\[\mathrm{CH_3CH(OH)COOH}\]

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(d) (i) For \(\mathrm{CH_3CH(NH_2)COOH}\):

I. In acidic medium:

\[\mathrm{CH_3CH(NH_3^+)COOH}\]

II. In alkaline medium:

\[\mathrm{CH_3CH(NH_2)COO^-}\]

(d) (ii)

Percentage of nitrogen in the salt:

\[\%\mathrm{N}=\frac{0.0313}{0.309}\times100=10.13\%\]

Hence, percentage of oxygen is:

\[\%\mathrm{O}=100-(60.5+6.5+10.13)=22.87\%\]

Element	Percentage	Relative number of moles	Simplest ratio
C	60.50	\(60.50/12.0=5.042\)	\(5.042/0.724=6.96\approx7\)
H	6.50	\(6.50/1.0=6.500\)	\(6.500/0.724=8.98\approx9\)
N	10.13	\(10.13/14.0=0.724\)	\(0.724/0.724=1\)
O	22.87	\(22.87/16.0=1.429\)	\(1.429/0.724=1.97\approx2\)

Therefore, the empirical formula of the salt is:

\[\boxed{\mathrm{C_7H_9NO_2}}\]

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(a)(i) The standard electrode potential, E°, is the potential of a half-cell measured relative to the standard hydrogen electrode under standard conditions: temperature 298 K, ion concentration 1.0 mol dm⁻³, and gas pressure 1 atm.

(ii) Two factors which affect electrode potential are:

1. concentration of ions in the electrolyte;
2. temperature.

(iii) Standard electrode potentials are used to:

1. predict the direction or feasibility of a redox reaction;
2. calculate the e.m.f. of an electrochemical cell.

(iv) A correctly labelled electrochemical cell is shown below.

Cell notation: \[\text{Zn(s)}\;|\;\text{Zn}^{2+}\text{(aq, 1 mol dm}^{-3}\text{)}\;||\;\text{Cu}^{2+}\text{(aq, 1 mol dm}^{-3}\text{)}\;|\;\text{Cu(s)}\] Zinc is the anode (negative electrode) where oxidation occurs, while copper is the cathode (positive electrode) where reduction occurs.

(v)

\[\begin{aligned}E^\circ_{\text{cell}}&=E^\circ_{\text{cathode}}-E^\circ_{\text{anode}}\\&=+0.34-(-0.76)\\&=+1.10\ \text{V}\end{aligned}\]

(b)(i)

1. Oxidation is the loss of electrons.
2. An oxidizing agent is a substance that accepts electrons and causes another substance to be oxidized.

(ii) In acidic solution, the balanced ionic equation is:

\[2\text{MnO}_4^-+16\text{H}^++10\text{I}^-\rightarrow2\text{Mn}^{2+}+5\text{I}_2+8\text{H}_2\text{O}\]

(c)

Oxide	Classification
Carbon(II) oxide, CO	Neutral
Sulphur(IV) oxide, SO2	Acidic
Aluminium oxide, Al2O3	Amphoteric
Lithium oxide, Li2O	Basic

(d) Hydrogen bonding is the strong intermolecular attraction between a hydrogen atom covalently bonded to nitrogen, oxygen, or fluorine in one molecule and a lone pair of electrons on nitrogen, oxygen, or fluorine in a neighbouring molecule.

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(a)(i) Nuclear fission

The splitting of a heavy atomic nucleus into two or more lighter nuclei of comparable mass, accompanied by the release of neutrons and a very large amount of energy, usually when the nucleus is struck by a neutron.

(a)(ii) Alpha and beta particles emitted from \(^{238}_{92}\)U to \(^{230}_{90}\)Th

Change in mass number: \(238 - 230 = 8\). Only alpha emission changes the mass number (by 4 each):

Change in atomic number: 2 alphas alone would give \(92 - (2\times 2) = 88\), but the product has Z = 90. Each beta emission raises Z by 1:

So 2 alpha particles and 2 beta particles were emitted.

(b) Equilibrium: A\(_2\)(g) + 3B\(_2\)(g) \(\rightleftharpoons\) 2AB\(_3\)(g); \(\Delta H = +x\) kJ mol\(^{-1}\) (endothermic)

• (i) Increase in concentration of B: equilibrium shifts to the right (forward) to use up the added B, giving more AB\(_3\).
• (ii) Decrease in pressure: the system shifts toward the side with the greater number of gas moles. The left has 4 moles and the right 2 moles, so equilibrium shifts to the left (backward), forming more A\(_2\) and B\(_2\).
• (iii) Addition of a catalyst: no effect on the equilibrium composition; it only speeds up the forward and backward reactions equally, so equilibrium is reached sooner.

(c) Trend in lattice energy of the sodium halides

From F\(^-\) to Br\(^-\) to I\(^-\) the ionic radius of the halide increases, so the distance between the Na\(^+\) and the halide ion grows. Lattice energy is inversely related to this interionic distance, so the electrostatic attraction weakens and the lattice energy falls: NaF > NaBr > NaI.

(d) Property of nitrogen(IV) oxide

• (i) 4Cu + 2NO\(_2\) \(\rightarrow\) 4CuO + N\(_2\): nitrogen is reduced from +4 to 0, so NO\(_2\) acts as an oxidising agent.
• (ii) H\(_2\)O + 2NO\(_2\) \(\rightarrow\) HNO\(_3\) + HNO\(_2\): nitrogen goes to +5 (in HNO\(_3\)) and +3 (in HNO\(_2\)), so NO\(_2\) undergoes disproportionation (it is simultaneously oxidised and reduced).

(e) Reactions in the blast furnace

• (i) Top (cooler zone) - reduction of the ore by carbon(II) oxide: \[ \text{Fe}_2\text{O}_3 + 3\text{CO} \rightarrow 2\text{Fe} + 3\text{CO}_2 \]
• (ii) Middle - decomposition of limestone and formation of carbon(II) oxide: \[ \text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2 \qquad \text{CO}_2 + \text{C} \rightarrow 2\text{CO} \]
• (iii) Bottom (hottest zone, at the tuyeres) - combustion of coke: \[ \text{C} + \text{O}_2 \rightarrow \text{CO}_2 \]

(Formation of slag, CaO + SiO\(_2\) \(\rightarrow\) CaSiO\(_3\), also occurs in the lower middle region.)

(f)(i) Two products of the destructive distillation of coal: coke and coal tar (coal gas and ammoniacal liquor are also produced).

(f)(ii) One use of each:

• Coke: used as a fuel and as the reducing agent in the extraction of iron in the blast furnace.
• Coal tar: used as a raw material for making dyes, drugs and antiseptics (and for surfacing roads).

Akọwa Nkọwa

(a)(i) I. Biotechnology: the use of living organisms (or their components, such as enzymes or micro-organisms) to make useful products or to carry out useful processes for man. II. Biogas: a mixture of gases (mainly methane and carbon(IV) oxide) produced by the anaerobic bacterial decomposition of organic matter, used as a fuel.

(a)(ii) Applications of biotechnology: production of alcoholic drinks/ethanol by fermentation; production of antibiotics and drugs; production of biogas; making of bread, yoghurt and cheese (any two).

(b)(i) Ethanol from sugar cane juice: the sugar cane juice, which contains sucrose, is diluted and yeast is added. The enzyme invertase (sucrase) in yeast hydrolyses sucrose to glucose and fructose, then zymase ferments these sugars to ethanol at about 30-40 °C in the absence of air:

The ethanol is then concentrated by fractional distillation.

(b)(ii) By-product: carbon(IV) oxide (CO₂).

(b)(iii) Uses of the by-product: making fizzy (carbonated) drinks; used as a fire extinguisher; solid CO₂ (dry ice) as a refrigerant.

(b)(iv) Ethanol from cane sugar is renewable because sugar cane is a crop that can be replanted and regrown within a short time, so the source is continuously replaceable. Ethanol from petroleum is non-renewable because petroleum is a fossil fuel formed over millions of years and cannot be replaced once used up.

(c) Heavy vs fine chemicals: heavy chemicals are produced in very large quantities, are relatively cheap and impure, e.g. tetraoxosulphate(VI) acid (H₂SO₄) or sodium trioxocarbonate(IV). Fine chemicals are produced in small quantities, are of high purity and are expensive, e.g. drugs/pharmaceuticals or dyes.

(d) Increasing order of deviation from ideal behaviour: O₂ < Cl₂ < HCl. Reason: deviation from ideal behaviour increases with the strength of intermolecular forces and with molecular size/polarity. O₂ is small and non-polar (least deviation); Cl₂ is larger and more polarisable; HCl is polar with strong dipole-dipole attractions, so it deviates most.

Akọwa Nkọwa

(a)

(i) Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration until they are uniformly distributed.

(ii) Charles’ law states that, at constant pressure, the volume of a fixed mass of gas is directly proportional to its absolute temperature.

(iii) The graph of volume against absolute temperature is a straight line passing through the origin.

(iv) At constant pressure:

\[\frac{V_1}{T_1}=\frac{V_2}{T_2}\]

\(V_1=150\text{ cm}^3\), \(V_2=2(150)=300\text{ cm}^3\), and \(T_1=27+273=300\text{ K}\).

\[T_2=\frac{V_2T_1}{V_1}=\frac{300\times300}{150}=600\text{ K}\]

Therefore, the required temperature is 600 K, or \(600-273=\mathbf{327^\circ C}\).

(v)

1. Increasing kinetic energy: solid < liquid < gas.
2. Increasing forces of cohesion: gas < liquid < solid.

(b)

(i) Le Chatelier’s principle states that when a system in equilibrium is subjected to a change in concentration, pressure or temperature, the equilibrium shifts in the direction that opposes the effect of the change.

(ii) In 100 g of the first oxide:

\[\text{mass of }M=100-11.1=88.9\text{ g}\]

Mass of oxygen combining with 100 g of \(M\):

\[\frac{11.1}{88.9}\times100=12.49\text{ g}\]

In 100 g of the second oxide:

\[\text{mass of }M=100-20.0=80.0\text{ g}\]

Mass of oxygen combining with 100 g of \(M\):

\[\frac{20.0}{80.0}\times100=25.0\text{ g}\]

Thus, the masses of oxygen which combine with the same mass of metal are:

\[12.49:25.0\approx1:2\]

This is a simple whole-number ratio. Hence, the results agree with the law of multiple proportions.

(c)

(i) Add water to the mixture and stir so that C dissolves. Filter the mixture. The filtrate contains C in solution, while the residue contains A and B. Evaporate the filtrate to dryness to obtain solid C.

Heat the residue gently to melt A and B, then separate the two liquids by fractional distillation. Collect A at \(117^\circ\text{C}\) and B at \(160^\circ\text{C}\).

(ii)

\[\text{Mass of C}=25.25-(7.52+8.48)\]

\[=25.25-16.00=9.25\text{ g}\]

\[\%\text{ by mass of C}=\frac{9.25}{25.25}\times100=36.6\%\]

Therefore, the percentage by mass of C in the mixture is 36.6%.

Akọwa Nkọwa

(a)(i) Rutherford's atomic structure: the atom has a very small, dense, positively charged nucleus at the centre where nearly all the mass is concentrated, with the negatively charged electrons moving in the mostly empty space around the nucleus.

(a)(ii) Atomic number vs mass number: the atomic number is the number of protons in the nucleus of an atom; the mass number is the total number of protons and neutrons in the nucleus.

(a)(iii) Chlorine exists as two isotopes, ³⁵Cl and ³⁷Cl, in the fixed ratio 3:1. The relative atomic mass is the weighted average of these isotopic masses, \(\frac{(35\times3)+(37\times1)}{4}=35.5\), which is not a whole number.

(b)(i) First ionization energy: the minimum energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous singly charged positive ions.

(b)(ii) Three properties of electrovalent compounds:

• They have high melting and boiling points.
• They are usually soluble in water but insoluble in organic solvents.
• They conduct electricity when molten or in aqueous solution.

(b)(iii) Each pair has the same number of electrons in the outermost shell (F and Cl each have 7; Mg and Ca each have 2). Since chemical properties depend on the number of valence electrons, members of the same group have similar chemical properties.

(c)(i) Homologous series: a family of organic compounds with the same general formula in which successive members differ by a CH₂ unit and show a gradual change in physical properties, e.g. the alkanes (CH₄, C₂H₆, C₃H₈...).

(c)(ii) Heterolytic fission: the breaking of a covalent bond in which both shared electrons go to one of the atoms, producing oppositely charged ions, e.g. \(\text{HCl} \to \text{H}^+ + \text{Cl}^-\).

(d) Indicators:

• (i) HCl vs NaOH (strong acid/strong base): methyl orange or phenolphthalein.
• (ii) HCl vs NH₄OH (strong acid/weak base): methyl orange.
• (iii) Ethanoic acid vs NaOH (weak acid/strong base): phenolphthalein.

(e) E = ammonium chloride (NH₄Cl, a solid chloride that sublimes); F = an alkali such as sodium hydroxide (NaOH); G = ammonia (NH₃), the choking gas that turns moist red litmus blue.