A-Level Chemistry Practice Questions

Question 1

Physical Chemistry AS Level

Calculate the number of moles in 9.2 g of sodium (Na).

Ar(Na) = 23

Solution:

Use: moles = mass / Ar
Given: mass = 9.2 g, Ar = 23
Calculate: moles = 9.2 / 23 = 0.4 mol

Answer: 0.4 mol

Question 2

Organic Chemistry A2 Level

Name the mechanism for the reaction between ethene and bromine.

Solution:

Ethene is an alkene (contains C=C double bond)
Bromine is an electrophile
The double bond has high electron density
Bromine molecule is polarized by the π-electrons
Br-Br bond breaks heterolytically
Br⁺ acts as electrophile and is attracted to double bond

Answer: Electrophilic addition

Question 3

Energetics AS Level

Define standard enthalpy of formation (ΔH°f).

Solution:

Standard enthalpy of formation is:
The enthalpy change when
ONE mole of a compound
Is formed from its elements
In their standard states
Under standard conditions (298 K, 100 kPa)

Answer: The enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions

Question 4

Inorganic Chemistry A2 Level

Write the electronic configuration of Fe²⁺ ion.

Atomic number of Fe = 26

Solution:

Fe atom (26 electrons): 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s²
Or: [Ar] 3d⁶ 4s²
Fe²⁺ has lost 2 electrons
Electrons are removed from 4s first (higher energy when occupied)
Fe²⁺ configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶

Answer: [Ar] 3d⁶ or 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶

Question 5

Kinetics Challenge

For the reaction: A + 2B → C, the rate equation is rate = k[A][B]²

What is the overall order of reaction?

Solution:

Rate equation: rate = k[A][B]²
Order with respect to A = 1 (power of [A])
Order with respect to B = 2 (power of [B])
Overall order = sum of individual orders
Overall order = 1 + 2 = 3

Answer: 3 (third order)

Question 6

Organic Chemistry A2 Level

Draw the structure of 2-methylbutanoic acid.

Solution:

"butanoic acid" = 4 carbon chain with -COOH group
"2-methyl" = CH₃ branch on carbon 2
Number from carboxylic acid end

Structure:

        CH₃
         |
    CH₃-CH-CH₂-COOH

Answer: CH₃CH(CH₃)CH₂COOH

Question 7

Equilibria Challenge

For the reaction: N₂ + 3H₂ ⇌ 2NH₃, ΔH = -92 kJ/mol

State the effect of increasing temperature on the equilibrium position.

Solution:

ΔH is negative, so forward reaction is exothermic
Reverse reaction is endothermic
Increasing temperature favours endothermic reaction (Le Chatelier's)
Equilibrium shifts to the left (reverse direction)
Less NH₃ produced, more N₂ and H₂

Answer: Equilibrium shifts to the left (towards reactants), yield of NH₃ decreases

Question 8

Transition Metals Challenge

What is the coordination number of [Cu(H₂O)₆]²⁺?

Solution:

Coordination number = number of coordinate bonds to central metal ion
Complex: [Cu(H₂O)₆]²⁺
There are 6 H₂O ligands
Each H₂O forms 1 coordinate bond
Total = 6 coordinate bonds

Answer: 6

Question 9

Organic Mechanisms Challenge

Name the mechanism for the reaction between CH₃Br and OH⁻.

Solution:

CH₃Br is a halogenoalkane (primary)
OH⁻ is a nucleophile (has lone pair of electrons)
OH⁻ attacks the δ+ carbon
C-Br bond breaks, Br⁻ leaves
This is nucleophilic substitution
For primary halogenoalkanes: SN2 mechanism

Answer: Nucleophilic substitution (SN2)

Question 10

Acids & Bases A2 Level

Calculate the pH of 0.1 mol dm⁻³ HCl solution.

Solution:

HCl is a strong acid (fully dissociates)
[H⁺] = [HCl] = 0.1 mol dm⁻³
Use: pH = -log₁₀[H⁺]
Calculate: pH = -log₁₀(0.1)
pH = -log₁₀(10⁻¹) = -(-1) = 1

Answer: pH = 1

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