2. (a) co₂ and sio₂ are both covalent compounds. explain briefly why co₂ is a gas whereas sio₂ is a solid under ordinary conditions. 2 marks (b) an element x reacts with bromine to form an ionic compound xbr₇. (i) state with reasons the physical state of xbr₇ at room - temperature. (ii) state with reasons whether x is a metal or a non - metal. (iii) predict two properties of xbr₇ other than its physical state. (iv) state the charge of an ion of x. 7 marks (c) (i) state the law of definite proportions. (ii) what volume of stock hcl with percentage purity of 36% and relative density 1.18 would be required to prepare 2.0 dm³ of 0.25 mol dm⁻³ hcl. m(hcl)=36.5 g mol⁻¹ 8 marks (d) iron was added to dilute tetraoxosulphate (vi) acid, the mixture was warmed gently and a gas was given off. the iron dissolved and a pale green solution was formed when more iron was added, the reaction eventually stopped and some iron was left. (i) write the formula of two ions present in dilute tetraoxosulphate (vi) acid. (ii) state why the mixture had to be warmed gently. (iii) what would be observed to indicate that a gas was being given off. (iv) name the gas. (v) explain why the reaction stopped. (vi) what is the name of the salt that gives the solution its green colour? (vii) state a method that could be used to separate the excess iron from the green solution. 8 marks 3. (a) (i) state hesss law of constant heat summation. (ii) sulphur (vi) oxide is formed according to the following reaction: 2so₂(g)+o₂(g)⇌2so₃(g) δh⁰ = - 1900 kj mol⁻¹ state and explain the effect of increase in pressure on the: (α) equilibrium position of the reaction; (β) equilibrium constant of the reaction. (iii) what would be the effect of an increase in temperature on the equilibrium position of the reaction? 10 marks (b) (i) explain why the production of aluminium may be considered as an environmentally friendly process but electrolysis of sodium chloride is not. (ii) name two major factors which would favour the siting of an aluminium smelter in a country. 6 marks

Question

2. (a) co₂ and sio₂ are both covalent compounds. explain briefly why co₂ is a gas whereas sio₂ is a solid under ordinary conditions. 2 marks (b) an element x reacts with bromine to form an ionic compound xbr₇. (i) state with reasons the physical state of xbr₇ at room - temperature. (ii) state with reasons whether x is a metal or a non - metal. (iii) predict two properties of xbr₇ other than its physical state. (iv) state the charge of an ion of x. 7 marks (c) (i) state the law of definite proportions. (ii) what volume of stock hcl with percentage purity of 36% and relative density 1.18 would be required to prepare 2.0 dm³ of 0.25 mol dm⁻³ hcl. m(hcl)=36.5 g mol⁻¹ 8 marks (d) iron was added to dilute tetraoxosulphate (vi) acid, the mixture was warmed gently and a gas was given off. the iron dissolved and a pale green solution was formed when more iron was added, the reaction eventually stopped and some iron was left. (i) write the formula of two ions present in dilute tetraoxosulphate (vi) acid. (ii) state why the mixture had to be warmed gently. (iii) what would be observed to indicate that a gas was being given off. (iv) name the gas. (v) explain why the reaction stopped. (vi) what is the name of the salt that gives the solution its green colour? (vii) state a method that could be used to separate the excess iron from the green solution. 8 marks 3. (a) (i) state hesss law of constant heat summation. (ii) sulphur (vi) oxide is formed according to the following reaction: 2so₂(g)+o₂(g)⇌2so₃(g)  δh⁰ = - 1900 kj mol⁻¹ state and explain the effect of increase in pressure on the: (α) equilibrium position of the reaction; (β) equilibrium constant of the reaction. (iii) what would be the effect of an increase in temperature on the equilibrium position of the reaction? 10 marks (b) (i) explain why the production of aluminium may be considered as an environmentally friendly process but electrolysis of sodium chloride is not. (ii) name two major factors which would favour the siting of an aluminium smelter in a country. 6 marks

Accepted Answer

### 2(a)
# Brief Explanations:
$CO_2$ has weak intermolecular forces (London - dispersion forces) between its simple molecular units, allowing it to be a gas. $SiO_2$ has a giant covalent structure with strong covalent bonds throughout the lattice, making it a solid.
# Answer:
$CO_2$ has weak intermolecular forces in its simple - molecular form, while $SiO_2$ has a giant covalent structure with strong covalent bonds.

### 2(b)(i)
# Brief Explanations:
Ionic compounds like $XBr_r$ usually have high melting and boiling points due to strong ionic bonds. So, at room temperature, $XBr_r$ is likely a solid.
# Answer:
Solid. Ionic compounds have strong ionic bonds resulting in high melting and boiling points.

### 2(b)(ii)
# Brief Explanations:
Since it forms an ionic compound with bromine, $X$ is a metal. Metals have a tendency to lose electrons to form positive ions in ionic compounds.
# Answer:
$X$ is a metal. It forms an ionic compound with bromine by losing electrons.

### 2(b)(iii)
# Brief Explanations:
Ionic compounds are good conductors of electricity in molten or aqueous state due to the presence of mobile ions. They also have high melting and boiling points.
# Answer:
Good conductor of electricity in molten/aqueous state; high melting and boiling points.

### 2(b)(iv)
# Brief Explanations:
Bromine forms a $Br^-$ ion. In an ionic compound, the charges must balance. So if the formula is $XBr_r$, the charge of $X$ is $+r$.
# Answer:
$+r$

### 2(c)(i)
# Brief Explanations:
The law of definite proportions states that in a pure chemical compound, elements are always present in definite proportions by mass.
# Answer:
In a pure chemical compound, elements are always present in definite proportions by mass.

### 2(c)(ii)
# Explanation:
## Step1: Calculate the molarity of stock HCl
The percentage purity is 36%, density $
ho = 1.18\ g\ cm^{-3}$. Assume 1 L of the stock solution. Mass of the solution $m=
ho V = 1.18\ g\ cm^{-3}	imes1000\ cm^{-3}=1180\ g$. Mass of HCl in the solution $m_{HCl}=0.36	imes1180\ g = 424.8\ g$. Molar mass of HCl $M = 36.5\ g\ mol^{-1}$. Molarity of stock solution $c_1=\frac{n}{V}=\frac{\frac{m_{HCl}}{M}}{V}=\frac{\frac{424.8\ g}{36.5\ g\ mol^{-1}}}{1\ L}=11.64\ mol\ dm^{-3}$
## Step2: Use dilution formula
The dilution formula is $c_1V_1 = c_2V_2$. We want $V_1$, $c_1 = 11.64\ mol\ dm^{-3}$, $c_2=0.25\ mol\ dm^{-3}$, $V_2 = 2.0\ dm^{3}$. So $V_1=\frac{c_2V_2}{c_1}=\frac{0.25\ mol\ dm^{-3}	imes2.0\ dm^{3}}{11.64\ mol\ dm^{-3}}=0.043\ dm^{3}=43\ cm^{3}$
# Answer:
$43\ cm^{3}$

### 2(d)(i)
# Brief Explanations:
The reaction is $Fe + H_2SO_4
ightarrow FeSO_4+H_2\uparrow$.
# Answer:
$Fe + H_2SO_4
ightarrow FeSO_4+H_2\uparrow$

### 2(d)(ii)
# Brief Explanations:
Warming gently increases the kinetic energy of the reactant particles, leading to more frequent and energetic collisions, thus increasing the reaction rate.
# Answer:
To increase the reaction rate by increasing the kinetic energy of reactant particles.

### 2(d)(iii)
# Brief Explanations:
Bubbles (effervescence) are observed when a gas is being given off.
# Answer:
Bubbles (effervescence) are seen.

### 2(d)(iv)
# Brief Explanations:
The gas given off is hydrogen ($H_2$).
# Answer:
Hydrogen

### 2(d)(v)
# Brief Explanations:
The reaction stopped because one of the reactants (either iron or acid) was completely consumed.
# Answer:
One of the reactants (iron or acid) was completely used up.

### 2(d)(vi)
# Brief Explanations:
The pale - green colour is due to the presence of $Fe^{2 + }$ ions in the solution.
# Answer:
$Fe^{2 + }$ ions

### 2(d)(vii)
# Brief Explanations:
Filtration can be used to separate the insoluble excess iron from the green solution (a liquid).
# Answer:
Filtration

### 3(a)(i)
# Brief Explanations:
Hess's law of constant Heat Summation states that the enthalpy change of a chemical reaction is the same whether the reaction takes place in one step or in a series of steps, provided the initial and final conditions are the same.
# Answer:
The enthalpy change of a chemical reaction is the same whether the reaction takes place in one step or in a series of steps, provided the initial and final conditions are the same.

### 3(a)(ii)(α)
# Brief Explanations:
For the reaction $2SO_2(g)+O_2(g)
ightleftharpoons2SO_3(g)$, there are 3 moles of gas on the left - hand side and 2 moles of gas on the right - hand side. An increase in pressure will shift the equilibrium position to the side with fewer moles of gas, i.e., to the right.
# Answer:
The equilibrium position shifts to the right. There are fewer moles of gas on the product side.

### 3(a)(ii)(β)
# Brief Explanations:
The equilibrium constant $K_p$ is a measure of the position of equilibrium in terms of partial pressures. For an increase in pressure (as explained above), the equilibrium shifts to the right, increasing the partial pressure of $SO_3$ and decreasing the partial pressures of $SO_2$ and $O_2$. So, $K_p$ increases.
# Answer:
$K_p$ increases. The equilibrium shifts to the right with an increase in pressure.

### 3(a)(iii)
# Brief Explanations:
The reaction $2SO_2(g)+O_2(g)
ightleftharpoons2SO_3(g)$ is exothermic ($\Delta H=- 1900\ kJ\ mol^{-1}$). An increase in temperature will shift the equilibrium in the endothermic direction (reverse direction) to absorb the added heat.
# Answer:
The equilibrium position shifts to the left. The reverse reaction is endothermic.

### 3(b)(i)
# Brief Explanations:
The production of aluminium can be considered environmentally friendly as the bauxite ore (main source of aluminium) is abundant, and the process can be made more energy - efficient with modern technologies. Electrolysis of sodium chloride produces chlorine gas which is a toxic gas and can cause environmental problems if not properly managed.
# Answer:
Aluminium production uses abundant bauxite and can be energy - efficient. Electrolysis of sodium chloride produces toxic chlorine gas.

### 3(b)(ii)
# Brief Explanations:
Two major factors for siting an aluminium smelter are the availability of cheap electricity (as the electrolysis process is energy - intensive) and the proximity to a source of bauxite (raw material).
# Answer:
Availability of cheap electricity; proximity to bauxite source.

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QUESTION IMAGE

Question

Explanation:

2(a)

Answer:

2(b)(i)