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Question 1 Report
(a)(i) Define the first ionization energy of an element
(ii) Consider the following table and use it to answer te question that follows
| Element | Li | Be | b | C | N | O | F | Ne |
| Atomic number | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| 1st I.E/kj mol\(^{-1}\) | 520 | 900 | 801 | 1086 | 1402 | 1314 | 1681 | 2081 |
Explain briefly why the first ionization energy of B is less than that of Be despite the fact that the atomic number of B is greater than that of Be.
(b) When Titanium chloride was electrolysed by passing 0.12 A current through the solution for 500 seconds, 0.015 g of titanium was deposited. What is the charge on the titanium ion?
[ IF= 96500 C, Ti= 48.0 ]
(c)(i) Aluminium can be obtained by the application of electrolysis. State the electrolyte which yields aluminium on electrolysis.
(ii) Name two major factors which would favour the siting of an aluminium smelter in a country.
(d)(i) Define the term paramagnetism.
(ii) Consider the following ions: \(^{24}\mathrm{Cr}^{2+}\), \(^{24}\mathrm{Cr}^{6+}\)
(I) Deduce the number of unpaired electrons in each of the ions.
(II) State which of the ions will have a greater power of paramagnetism
(l) Give a reason for the answer stated in (d)(ii)(II)
(a)(i) The first ionization energy of an element is the amount of energy required to remove one electron from a neutral atom of that element in the gaseous state. (ii) The missing value in the table is 730 kJ mol⁻¹ for the first ionization energy of lithium (Li). Explanation for (a): The first ionization energy of B is less than that of Be because B has an electron in a p-orbital, which is further away from the nucleus than the s-orbital electrons in Be. As a result, the attraction between the nucleus and the outermost electron is weaker in B than in Be, making it easier to remove an electron from B. (b) The amount of charge on the titanium ion can be calculated using the formula: Charge = (Current x Time x IF) / Mass where IF is the Faraday constant and equals 96500 C mol⁻¹. Plugging in the values given, we get: Charge = (0.12 A x 500 s x 96500 C mol⁻¹) / 0.015 g Charge = 1.934 x 10⁶ C mol⁻¹ Since the charge on a single titanium ion is 4+, we can calculate the number of moles of titanium deposited by dividing the mass by the molar mass: n(Ti) = 0.015 g / 48.0 g mol⁻¹ = 3.125 x 10⁻⁴ mol Dividing the total charge by the number of moles of titanium gives us the charge on a single titanium ion: Charge on Ti⁴⁺ ion = (1.934 x 10⁶ C mol⁻¹) / (3.125 x 10⁻⁴ mol) = 6.188 x 10⁹ C (c)(i) The electrolyte which yields aluminium on electrolysis is molten cryolite (Na₃AlF₆) mixed with aluminium oxide (Al₂O₃). (ii) Two major factors which would favour the siting of an aluminium smelter in a country are the availability of cheap electricity and the presence of bauxite ore, which is the raw material used to produce aluminium. (d)(i) Paramagnetism is the property of an atom, ion, or molecule that has unpaired electrons and is attracted by a magnetic field. (ii) For 24Cr2+, there are 4 unpaired electrons, while for 24Cr6+, there are no unpaired electrons. Therefore, 24Cr2+ will have a greater power of paramagnetism. Explanation for (d)(ii): The power of paramagnetism is directly proportional to the number of unpaired electrons. Since 24Cr2+ has 4 unpaired electrons, it will have a greater power of paramagnetism than 24Cr6+, which has no unpaired electrons. This is because the unpaired electrons in 24Cr2+ are available for alignment with an external magnetic field, whereas the paired electrons in 24Cr6+ are not.
Answer Details
(a)(i) The first ionization energy of an element is the amount of energy required to remove one electron from a neutral atom of that element in the gaseous state. (ii) The missing value in the table is 730 kJ mol⁻¹ for the first ionization energy of lithium (Li). Explanation for (a): The first ionization energy of B is less than that of Be because B has an electron in a p-orbital, which is further away from the nucleus than the s-orbital electrons in Be. As a result, the attraction between the nucleus and the outermost electron is weaker in B than in Be, making it easier to remove an electron from B. (b) The amount of charge on the titanium ion can be calculated using the formula: Charge = (Current x Time x IF) / Mass where IF is the Faraday constant and equals 96500 C mol⁻¹. Plugging in the values given, we get: Charge = (0.12 A x 500 s x 96500 C mol⁻¹) / 0.015 g Charge = 1.934 x 10⁶ C mol⁻¹ Since the charge on a single titanium ion is 4+, we can calculate the number of moles of titanium deposited by dividing the mass by the molar mass: n(Ti) = 0.015 g / 48.0 g mol⁻¹ = 3.125 x 10⁻⁴ mol Dividing the total charge by the number of moles of titanium gives us the charge on a single titanium ion: Charge on Ti⁴⁺ ion = (1.934 x 10⁶ C mol⁻¹) / (3.125 x 10⁻⁴ mol) = 6.188 x 10⁹ C (c)(i) The electrolyte which yields aluminium on electrolysis is molten cryolite (Na₃AlF₆) mixed with aluminium oxide (Al₂O₃). (ii) Two major factors which would favour the siting of an aluminium smelter in a country are the availability of cheap electricity and the presence of bauxite ore, which is the raw material used to produce aluminium. (d)(i) Paramagnetism is the property of an atom, ion, or molecule that has unpaired electrons and is attracted by a magnetic field. (ii) For 24Cr2+, there are 4 unpaired electrons, while for 24Cr6+, there are no unpaired electrons. Therefore, 24Cr2+ will have a greater power of paramagnetism. Explanation for (d)(ii): The power of paramagnetism is directly proportional to the number of unpaired electrons. Since 24Cr2+ has 4 unpaired electrons, it will have a greater power of paramagnetism than 24Cr6+, which has no unpaired electrons. This is because the unpaired electrons in 24Cr2+ are available for alignment with an external magnetic field, whereas the paired electrons in 24Cr6+ are not.
Question 2 Report
(a) Describe the observation that would be made when-----
i. Sulphur is heated from room temperature till 1190C
ii. 50% trioxonitrate(V) acid acts on copper tunings
(b) i. State two gaseous pollutants that can be generated by burning coal.
ii. What gas is responsible for most of the explosions in coal mines?
iii. The mining of coal leads to environmental pollution. State two environmental effects of the mining activity.
iv. Explain briefly why coal burns more easily when it is in pieces than in lump form
v. Name the non-volitile residue after the destructive distillation of coal
(c) i. Describe a chemical test for water
ii. a. State the effect of boiling a temporary hard water
b. State the effect of adding sodium trioxocarbonate(IV) crystals to permanent hard water
iii. Write an equation for the process of boiling a temporary hard water
(a) i. When sulphur is heated from room temperature till 1190°C, it changes from a solid state to a liquid state and then to a gaseous state. At 1190°C, sulphur melts to form a reddish-brown liquid and further heating leads to the vaporization of the liquid to form a gas with a pale blue flame. ii. When 50% trioxonitrate(V) acid acts on copper tunings, brown nitrogen dioxide gas is produced. The copper is oxidized to copper(II) nitrate and the nitrogen dioxide is liberated. The brown coloration is due to the presence of the nitrogen dioxide gas. (b) i. Two gaseous pollutants that can be generated by burning coal are sulfur dioxide and carbon dioxide. ii. Methane gas is responsible for most of the explosions in coal mines. iii. Two environmental effects of coal mining activity are air pollution and water pollution. iv. Coal burns more easily when it is in pieces because the surface area of the coal is increased, allowing more oxygen to react with it. v. The non-volatile residue after the destructive distillation of coal is coal tar. (c) i. A chemical test for water is the anhydrous copper sulfate test. When anhydrous copper sulfate is added to water, it turns from white to blue, indicating the presence of water. ii. a. Boiling a temporary hard water causes the calcium and magnesium ions responsible for the hardness to precipitate out of solution, leaving soft water. b. Adding sodium trioxocarbonate(IV) crystals to permanent hard water causes the calcium and magnesium ions responsible for the hardness to precipitate out of solution, leaving soft water. iii. The equation for the process of boiling a temporary hard water is: Ca(HCO3)2 → CaCO3 + CO2 + H2O.
Answer Details
(a) i. When sulphur is heated from room temperature till 1190°C, it changes from a solid state to a liquid state and then to a gaseous state. At 1190°C, sulphur melts to form a reddish-brown liquid and further heating leads to the vaporization of the liquid to form a gas with a pale blue flame. ii. When 50% trioxonitrate(V) acid acts on copper tunings, brown nitrogen dioxide gas is produced. The copper is oxidized to copper(II) nitrate and the nitrogen dioxide is liberated. The brown coloration is due to the presence of the nitrogen dioxide gas. (b) i. Two gaseous pollutants that can be generated by burning coal are sulfur dioxide and carbon dioxide. ii. Methane gas is responsible for most of the explosions in coal mines. iii. Two environmental effects of coal mining activity are air pollution and water pollution. iv. Coal burns more easily when it is in pieces because the surface area of the coal is increased, allowing more oxygen to react with it. v. The non-volatile residue after the destructive distillation of coal is coal tar. (c) i. A chemical test for water is the anhydrous copper sulfate test. When anhydrous copper sulfate is added to water, it turns from white to blue, indicating the presence of water. ii. a. Boiling a temporary hard water causes the calcium and magnesium ions responsible for the hardness to precipitate out of solution, leaving soft water. b. Adding sodium trioxocarbonate(IV) crystals to permanent hard water causes the calcium and magnesium ions responsible for the hardness to precipitate out of solution, leaving soft water. iii. The equation for the process of boiling a temporary hard water is: Ca(HCO3)2 → CaCO3 + CO2 + H2O.
Question 3 Report
a) (i) Define the term Avogadro's number.
(ii) If 2.30 g of an oxide of nitrogen, x, contains \(3.01 x 10^{22}\) molecules, calculate the molar mass of x.
(iii) Deduce the formula of x. N, =6.02 x 10", N =14.0, O = 16.0]
(b)(i) Describe briefly what happens when each of the following substances are added to water:
| (I) \(\mathrm{CCI}_{4}\); | (II) \(\mathrm{SiCI}_{4}\), |
(ii) Explain briefly why the reactions in (a)(i), (b)(i), (I) and (b)(ii) (II) are different Study the diagram below and answer the questions that follow.
(c) Study the diagram below and answer the questions that follow.
%IMG%
(i) What is the set up used for?
a) (i) Avogadro's number is the number of particles (atoms, molecules, ions, etc.) present in one mole of a substance. It is approximately equal to 6.02 × 1023 particles per mole. (ii) First, we need to calculate the number of moles of x in the given sample: Number of moles = Number of particles / Avogadro's number Number of moles = 3.01 × 1022 / 6.02 × 1023 Number of moles = 0.05 mol Molar mass of x = Mass of x / Number of moles Molar mass of x = 2.30 g / 0.05 mol Molar mass of x = 46 g/mol (iii) The empirical formula of x can be determined by finding the ratio of the atoms present in it. Since the molar mass of x is 46 g/mol and it contains nitrogen and oxygen, we can assume that the formula is NxOy. The ratio of N to O can be determined using the atomic masses of N and O and the given molar mass: Molar mass of NxOy = (N × 14.0) + (y × 16.0) = 46 N + y = 3.29 Since N and y must be integers, the closest possible ratio is N:O = 1:2. Therefore, the formula of x is N2O. (b) (i) When CCl4 is added to water, it does not dissolve as it is a nonpolar substance and water is a polar solvent. When SiCl4 is added to water, it reacts with water to form HCl and SiO2, which precipitates as a white solid. (ii) The reactions in (a)(i), (b)(i), (I), and (b)(ii) are different because they involve different substances and chemical reactions with water. In (a)(i), an oxide of nitrogen is being analyzed for its molar mass and formula. In (b)(i), two substances that are insoluble or react with water are being added to it. In (I), Pb(NO3)2 is being added to NaCl solution to precipitate PbCl2. In (b)(ii), SiCl4 is reacting with water to form HCl and SiO2. (c) (i) The setup is a simple distillation apparatus. It is used to separate a mixture of liquids with different boiling points by heating the mixture and collecting the condensed vapors. The mixture is heated in a distillation flask, and the vapors travel up the fractionating column, which contains several trays or packing material. The vapor with the lower boiling point condenses on the trays or packing, and the vapor with the higher boiling point continues to the condenser, where it is cooled and collected as a liquid. This allows for the separation of the components of the mixture based on their boiling points.
Answer Details
a) (i) Avogadro's number is the number of particles (atoms, molecules, ions, etc.) present in one mole of a substance. It is approximately equal to 6.02 × 1023 particles per mole. (ii) First, we need to calculate the number of moles of x in the given sample: Number of moles = Number of particles / Avogadro's number Number of moles = 3.01 × 1022 / 6.02 × 1023 Number of moles = 0.05 mol Molar mass of x = Mass of x / Number of moles Molar mass of x = 2.30 g / 0.05 mol Molar mass of x = 46 g/mol (iii) The empirical formula of x can be determined by finding the ratio of the atoms present in it. Since the molar mass of x is 46 g/mol and it contains nitrogen and oxygen, we can assume that the formula is NxOy. The ratio of N to O can be determined using the atomic masses of N and O and the given molar mass: Molar mass of NxOy = (N × 14.0) + (y × 16.0) = 46 N + y = 3.29 Since N and y must be integers, the closest possible ratio is N:O = 1:2. Therefore, the formula of x is N2O. (b) (i) When CCl4 is added to water, it does not dissolve as it is a nonpolar substance and water is a polar solvent. When SiCl4 is added to water, it reacts with water to form HCl and SiO2, which precipitates as a white solid. (ii) The reactions in (a)(i), (b)(i), (I), and (b)(ii) are different because they involve different substances and chemical reactions with water. In (a)(i), an oxide of nitrogen is being analyzed for its molar mass and formula. In (b)(i), two substances that are insoluble or react with water are being added to it. In (I), Pb(NO3)2 is being added to NaCl solution to precipitate PbCl2. In (b)(ii), SiCl4 is reacting with water to form HCl and SiO2. (c) (i) The setup is a simple distillation apparatus. It is used to separate a mixture of liquids with different boiling points by heating the mixture and collecting the condensed vapors. The mixture is heated in a distillation flask, and the vapors travel up the fractionating column, which contains several trays or packing material. The vapor with the lower boiling point condenses on the trays or packing, and the vapor with the higher boiling point continues to the condenser, where it is cooled and collected as a liquid. This allows for the separation of the components of the mixture based on their boiling points.
Question 4 Report
(a) i. State two conditions used in the Haber process
ii. Explain briefly the effect of increasing the pressure on the rate of reaction in the Haber process.
(b) i. A mixture of nitrogen(IV) oxide and oxygen is bubbled into warm water to produce trioxonitrate(V) oxide, write a balanced chemical equation for the reaction.
ii. Using a balanced chemical equation only, explain what would happen if nitrogen(IV) oxide is bubbled into warm water.
iii.
Compare the gases evolved when trioxonitrate(V) acid decomposes under each of the following properties:
i. pH
ii. Solubility in water
iii. Reaction with carbon(II) oxide
(c) i. Name two oxides of sulphur
ii. Write a balanced equation for the reaction between each of the named oxides(Sulphur(IV) oxide, Sulphur (VI) oxide) and water
(d) i. Name one calcium compound
a, Used to dry ammonia gas
b. Used in the manufacture of cement
c. That causes hardness in water
d. Name one calcium compound
(a) i. The two conditions used in the Haber process are high pressure and high temperature. ii. Increasing the pressure increases the rate of reaction in the Haber process because it shifts the equilibrium towards the side with fewer gas molecules, in accordance with Le Chatelier's principle. (b) i. 2NO + O2 → 2NO3 ii. When nitrogen(IV) oxide is bubbled into warm water, it reacts to form nitric acid (HNO3) and nitric oxide (NO). (c) i. The two oxides of sulfur are sulfur dioxide (SO2) and sulfur trioxide (SO3). ii. Balanced chemical equations for the reactions between the named oxides and water are: SO2 + H2O → H2SO3 SO3 + H2O → H2SO4 (d) i. Calcium chloride is used to dry ammonia gas. ii. Calcium silicate is used in the manufacture of cement. iii. Calcium carbonate causes hardness in water. iv. Calcium hydroxide is also known as slaked lime and is used in various applications such as water treatment and food processing.
Answer Details
(a) i. The two conditions used in the Haber process are high pressure and high temperature. ii. Increasing the pressure increases the rate of reaction in the Haber process because it shifts the equilibrium towards the side with fewer gas molecules, in accordance with Le Chatelier's principle. (b) i. 2NO + O2 → 2NO3 ii. When nitrogen(IV) oxide is bubbled into warm water, it reacts to form nitric acid (HNO3) and nitric oxide (NO). (c) i. The two oxides of sulfur are sulfur dioxide (SO2) and sulfur trioxide (SO3). ii. Balanced chemical equations for the reactions between the named oxides and water are: SO2 + H2O → H2SO3 SO3 + H2O → H2SO4 (d) i. Calcium chloride is used to dry ammonia gas. ii. Calcium silicate is used in the manufacture of cement. iii. Calcium carbonate causes hardness in water. iv. Calcium hydroxide is also known as slaked lime and is used in various applications such as water treatment and food processing.
Question 5 Report
(a)i. Define an acid according to the Lewis concept
ii. Give one example of a Lewis acid
(b) Explain salting out in soap preparation
(c) State the reagent and condition necessary for the following conversion
\[ \mathrm{H{-}C{\equiv}C{-}H \rightarrow Ag{-}C{\equiv}C{-}Ag} \]
(d) What is the percentage abundance of an isotope?
(e)i. Why does the element with atomic number 18 not have an oxide?
ii. Explain why chlorine(I) oxide has a low melting point
(f). Describe a test to distinguish between concentrated HNO3 and concentrated H2SO4
(g) State two differences between an electrochemical cell and an electrolytic cell
(h) How does the trend in ionization energy affect the reactivity of group 1 elements?
(i).Define the term molecular formula
(j) State which of the gases H2 and NH3 would deviate more from ideal behaviour. Give reasons for the answer stated above
(a) i. According to the Lewis concept, an acid is defined as a substance that can accept a pair of electrons (an electron pair acceptor) during a chemical reaction. In other words, acids are substances that can form coordinate covalent bonds by accepting electron pairs from other molecules or ions. ii. An example of a Lewis acid is boron trifluoride (BF3). BF3 has an incomplete octet and can accept an electron pair from a Lewis base to form a coordinate covalent bond. (b) Salting out in soap preparation refers to the process of adding salt (such as sodium chloride) to a soap mixture to separate the soap from the aqueous solution. When salt is added, it reduces the solubility of soap in water, causing the soap to precipitate or separate out. This occurs because the salt ions compete with the soap molecules for the water molecules, disrupting the soap-water interactions and promoting the formation of soap aggregates or micelles. (c) The reagent and condition necessary for the conversion of H-C≡C-H to Ag-C≡C-Ag is silver nitrate (AgNO3) and ammonia (NH3) as a complexing agent. The reaction takes place in the presence of sunlight or UV light. (d) The percentage abundance of an isotope refers to the relative abundance or proportion of a specific isotope in a naturally occurring sample of an element. It is expressed as a percentage and represents the fraction of the total number of atoms of the element that is composed of the specific isotope. (e) i. The element with atomic number 18 is argon (Ar), which belongs to the noble gas group. Noble gases are known for their stable electronic configurations and inert nature. Since argon already has a complete octet in its outer electron shell, it does not readily form compounds, including oxides. ii. Chlorine(I) oxide (Cl2O) has a low melting point due to its weak intermolecular forces. It exists as discrete Cl2O molecules held together by relatively weak van der Waals forces. These forces are easily overcome, resulting in a low melting point for the compound. (f) A test to distinguish between concentrated HNO3 (nitric acid) and concentrated H2SO4 (sulfuric acid) is to add a small piece of copper metal to each acid. Nitric acid is a strong oxidizing agent and will react with the copper, producing brown nitrogen dioxide gas (NO2) and dissolving the copper. Sulfuric acid, on the other hand, is not a strong oxidizing agent and will not react with copper under normal conditions. (g) Two differences between an electrochemical cell and an electrolytic cell are: 1. In an electrochemical cell (such as a voltaic cell or a galvanic cell), the chemical reactions are spontaneous and produce electrical energy. In contrast, an electrolytic cell requires an external source of electrical energy to drive non-spontaneous reactions. 2. In an electrochemical cell, electrons flow spontaneously from the anode (where oxidation occurs) to the cathode (where reduction occurs). In an electrolytic cell, the direction of electron flow is reversed by the external power source to drive the non-spontaneous reactions. (h) The trend in ionization energy, which refers to the energy required to remove an electron from an atom or ion, affects the reactivity of group 1 elements (alkali metals). As we move down the group from top to bottom, the ionization energy decreases. This means that the outermost electron in alkali metals is increasingly farther from the nucleus and more loosely held. As a result, the reactivity of alkali metals increases down the group because it becomes easier for
Answer Details
(a) i. According to the Lewis concept, an acid is defined as a substance that can accept a pair of electrons (an electron pair acceptor) during a chemical reaction. In other words, acids are substances that can form coordinate covalent bonds by accepting electron pairs from other molecules or ions. ii. An example of a Lewis acid is boron trifluoride (BF3). BF3 has an incomplete octet and can accept an electron pair from a Lewis base to form a coordinate covalent bond. (b) Salting out in soap preparation refers to the process of adding salt (such as sodium chloride) to a soap mixture to separate the soap from the aqueous solution. When salt is added, it reduces the solubility of soap in water, causing the soap to precipitate or separate out. This occurs because the salt ions compete with the soap molecules for the water molecules, disrupting the soap-water interactions and promoting the formation of soap aggregates or micelles. (c) The reagent and condition necessary for the conversion of H-C≡C-H to Ag-C≡C-Ag is silver nitrate (AgNO3) and ammonia (NH3) as a complexing agent. The reaction takes place in the presence of sunlight or UV light. (d) The percentage abundance of an isotope refers to the relative abundance or proportion of a specific isotope in a naturally occurring sample of an element. It is expressed as a percentage and represents the fraction of the total number of atoms of the element that is composed of the specific isotope. (e) i. The element with atomic number 18 is argon (Ar), which belongs to the noble gas group. Noble gases are known for their stable electronic configurations and inert nature. Since argon already has a complete octet in its outer electron shell, it does not readily form compounds, including oxides. ii. Chlorine(I) oxide (Cl2O) has a low melting point due to its weak intermolecular forces. It exists as discrete Cl2O molecules held together by relatively weak van der Waals forces. These forces are easily overcome, resulting in a low melting point for the compound. (f) A test to distinguish between concentrated HNO3 (nitric acid) and concentrated H2SO4 (sulfuric acid) is to add a small piece of copper metal to each acid. Nitric acid is a strong oxidizing agent and will react with the copper, producing brown nitrogen dioxide gas (NO2) and dissolving the copper. Sulfuric acid, on the other hand, is not a strong oxidizing agent and will not react with copper under normal conditions. (g) Two differences between an electrochemical cell and an electrolytic cell are: 1. In an electrochemical cell (such as a voltaic cell or a galvanic cell), the chemical reactions are spontaneous and produce electrical energy. In contrast, an electrolytic cell requires an external source of electrical energy to drive non-spontaneous reactions. 2. In an electrochemical cell, electrons flow spontaneously from the anode (where oxidation occurs) to the cathode (where reduction occurs). In an electrolytic cell, the direction of electron flow is reversed by the external power source to drive the non-spontaneous reactions. (h) The trend in ionization energy, which refers to the energy required to remove an electron from an atom or ion, affects the reactivity of group 1 elements (alkali metals). As we move down the group from top to bottom, the ionization energy decreases. This means that the outermost electron in alkali metals is increasingly farther from the nucleus and more loosely held. As a result, the reactivity of alkali metals increases down the group because it becomes easier for
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