EmSAT Chemistry 3 — Questions and Answers
Question 1: Which type of bonding is present in sodium chloride (NaCl)?
- Covalent bonding
- Ionic bonding (Correct answer)
- Metallic bonding
- Hydrogen bonding
Correct answer: Ionic bonding
NaCl is formed by the transfer of an electron from sodium to chlorine, creating an ionic bond between Na⁺ and Cl⁻ ions.
Question 2: What is the oxidation state of sulfur in H₂SO₄?
- +4
- +6 (Correct answer)
- -2
- +2
Correct answer: +6
In H₂SO₄, hydrogen is +1 (×2 = +2) and oxygen is -2 (×4 = -8), so sulfur must be +6 to give an overall charge of zero.
Question 3: A reaction has a negative ΔH and a negative ΔS. Under which condition is the reaction spontaneous?
- At all temperatures
- At high temperatures only
- At low temperatures only (Correct answer)
- Never spontaneous
Correct answer: At low temperatures only
When ΔH < 0 and ΔS < 0, ΔG = ΔH – TΔS is negative (spontaneous) only at low temperatures where the enthalpy term dominates.
Question 4: Which of the following is an example of a nucleophilic substitution reaction?
- Combustion of methane
- Reaction of bromoethane with KOH(aq) (Correct answer)
- Cracking of hexane
- Chlorination of benzene
Correct answer: Reaction of bromoethane with KOH(aq)
OH⁻ acts as a nucleophile attacking the carbon bonded to Br in bromoethane, replacing Br in an SN2-type substitution.
Question 5: What does Le Chatelier's principle predict when pressure is increased on the equilibrium N₂(g) + 3H₂(g) ⇌ 2NH₃(g)?
- Equilibrium shifts left, producing more N₂ and H₂
- Equilibrium shifts right, producing more NH₃ (Correct answer)
- Equilibrium is unaffected
- Kc increases
Correct answer: Equilibrium shifts right, producing more NH₃
Increasing pressure shifts equilibrium toward the side with fewer moles of gas; the right side has 2 moles vs. 4 on the left, so more NH₃ is produced.
Question 6: Which property best distinguishes a strong acid from a weak acid of the same concentration?
- Molar mass
- Degree of ionisation (Correct answer)
- Boiling point
- Colour in solution
Correct answer: Degree of ionisation
A strong acid fully ionises in water (degree ≈ 100%), while a weak acid only partially ionises, resulting in a lower H⁺ concentration.
Question 7: In an electrochemical cell, oxidation occurs at the:
- Cathode
- Anode (Correct answer)
- Salt bridge
- External circuit wire
Correct answer: Anode
Oxidation is the loss of electrons, and this always occurs at the anode of an electrochemical cell.
EmSAT Chemistry 3
Which type of bonding is present in sodium chloride (NaCl)?