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 xbrᵣ.
(i) state with reasons the physical state of xbrᵣ at room temperature.
(ii) state with reasons whether x is a metal or a non - metal.
(iii) predict two properties of xbrᵣ 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 the physical state 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

Accepted Answer

### 2. (a)
# Brief Explanations:
$CO_2$ is a simple molecular compound with weak intermolecular forces (London - dispersion forces). These are easily overcome at ordinary conditions, so it is a gas. $SiO_2$ has a giant covalent structure with strong covalent bonds throughout the lattice, requiring a large amount of energy to break, making it a solid.
# Answer:
$CO_2$ has weak intermolecular forces, $SiO_2$ has a giant covalent structure.

### 2. (b) (i)
# Brief Explanations:
Ionic compounds like $XBr_x$ typically have high melting and boiling points due to strong ionic bonds. So at room temperature, $XBr_x$ is a solid.
# Answer:
Solid. Strong ionic bonds result in high melting - point.

### 2. (b) (ii)
# Brief Explanations:
An element that forms an ionic compound with bromine (a non - metal) by losing electrons is a metal. Metals tend to form positive ions by losing electrons to non - metals.
# Answer:
Metal. It forms a positive ion by losing electrons to bromine.

### 2. (b) (iii)
# Brief Explanations:
Physical state is not a reliable predictor of whether an element is a metal or non - metal. For example, mercury is a liquid metal and carbon (graphite) is a solid non - metal. Other properties like electrical conductivity, malleability etc. can be used. Metals are good conductors of electricity in the solid or molten state, non - metals are usually poor conductors.
# Answer:
Electrical conductivity. Metals are good conductors, non - metals are poor conductors.

### 2. (b) (iv)
# Brief Explanations:
Since it forms an ionic compound with bromine ($Br^-$), and bromine gains one electron to form its ion, if the formula is $XBr_x$, the charge of the ion of $X$ is $+x$.
# Answer:
$+x$

### 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$.
Let's assume we have 1 L of the solution. The mass of the solution $m=
ho V = 1.18\ g/cm^3	imes1000\ cm^3 = 1180\ g$.
The mass of HCl in the solution $m_{HCl}=0.36	imes1180\ g = 424.8\ g$.
The molar mass of HCl $M = 36.5\ g/mol$.
The molarity of stock HCl $c_1=\frac{n}{V}=\frac{\frac{m_{HCl}}{M}}{V}=\frac{\frac{424.8\ g}{36.5\ g/mol}}{1\ L}=11.64\ mol/dm^3$.
## Step2: Use the dilution formula $c_1V_1 = c_2V_2$
We want to prepare $V_2 = 2.0\ dm^3$ of $c_2 = 0.25\ mol/dm^3$ HCl.
$V_1=\frac{c_2V_2}{c_1}=\frac{0.25\ mol/dm^3	imes2.0\ dm^3}{11.64\ mol/dm^3}=0.043\ dm^3 = 43\ cm^3$.
# Answer:
$43\ cm^3$

### 2. (d) (i)
# Brief Explanations:
The formula of the two ions in dilute tetraoxosulphate(VI) acid ($H_2SO_4$) are $H^+$ and $SO_4^{2 - }$.
# Answer:
$H^+$, $SO_4^{2 - }$

### 2. (d) (ii)
# Brief Explanations:
The mixture was warmed gently, which increases the rate of the reaction between iron and the acid.
# Answer:
Warming increases the reaction rate.

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

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

### 2. (d) (v)
# Brief Explanations:
The reaction stopped because the iron (the reactant) was completely consumed.
# Answer:
Iron was completely consumed.

### 2. (d) (vi)
# Brief Explanations:
The salt that gives the solution its green colour is iron(II) sulphate ($FeSO_4$).
# Answer:
Iron(II) sulphate.

### 2. (d) (vii)
# Brief Explanations:
Filtration can be used to separate the excess iron (solid) from the green solution (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) ($\alpha$)
# Brief Explanations:
The reaction $2SO_{2(g)}+O_{2(g)}
ightleftharpoons2SO_{3(g)}$ has a decrease in the number of moles of gas from 3 moles of reactants to 2 moles of products. An increase in pressure will shift the equilibrium position to the right (towards the side with fewer moles of gas) to reduce the pressure according to Le - Chatelier's principle.
# Answer:
The equilibrium position shifts to the right.

### 3. (a) (ii) ($\beta$)
# Brief Explanations:
The equilibrium constant ($K_p$ or $K_c$) of a reaction only depends on temperature. So an increase in pressure has no effect on the equilibrium constant.
# Answer:
No effect.

### 3. (a) (iii)
# Brief Explanations:
The reaction is exothermic ($\Delta H=- 1900\ kJ/mol$). According to Le - Chatelier's principle, an increase in temperature will shift the equilibrium position to the left (the endothermic direction) to absorb the added heat.
# Answer:
The equilibrium position shifts to the left.

### 3. (b) (i)
# Brief Explanations:
The production of aluminium can be considered environmentally friendly because bauxite (the main ore of aluminium) is abundant, and modern electrolysis processes can be energy - efficient and use recycled materials. Electrolysis of sodium chloride produces chlorine gas, which is a toxic gas if not properly handled, and also requires a large amount of energy.
# Answer:
Aluminium production can use abundant ore and be energy - efficient with recycling. Sodium chloride electrolysis produces toxic chlorine and is energy - intensive.

### 3. (b) (ii)
# Brief Explanations:
Two major factors for siting an aluminium smelter are the availability of cheap electricity (since electrolysis is energy - intensive) and proximity to bauxite sources (to reduce transportation costs).
# Answer:
Availability of cheap electricity, proximity to bauxite sources.

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QUESTION IMAGE

Question

Explanation:

2. (a)

Answer:

2. (b) (i)