2. Give short answer.
(i) Write the equation for the self-ionization of water.
Answer: The self-ionization (autoionization) of water is the reaction where two water molecules react to form a hydronium ion (H₃O⁺) and a hydroxide ion (OH⁻): 2H₂O(l) [source symbol unavailable] H₃O⁺(aq) + OH⁻(aq)
The equilibrium constant for this process is Kw = [H₃O⁺][OH⁻] = 1.0 × 10⁻¹⁴ at 25°C.
(ii) Define and give examples of Arrhenius acids.
Answer: An Arrhenius acid is a substance that produces hydrogen ions (H⁺) when dissolved in water.
Examples:
HCl(aq) [source symbol unavailable] H⁺(aq) + Cl⁻(aq) HNO₃(aq) [source symbol unavailable] H⁺(aq) + NO₃⁻(aq) H₂SO₄(aq) [source symbol unavailable] 2H⁺(aq) + SO₄²⁻(aq)
(iii) Why HCl acts as a strong acid?
Answer: HCl acts as a strong acid because it ionizes completely (100%) in water, producing a high concentration of hydrogen ions (H⁺). The H-Cl bond is highly polar, and the chloride ion (Cl⁻) is a very stable anion, making it easy for HCl to donate a proton. Strong acids have a very large Ka value.
(iv) Why NH₄⁺ acts as Bronsted-Lowry base?
Answer: NH₄⁺ does not act as a Bronsted-Lowry base; it acts as a Bronsted-Lowry acid. It can donate a proton (H⁺) to a base to form NH₃: NH₄⁺ + B [source symbol unavailable] NH₃ + BH⁺. (Note: If the question meant NH₃, then NH₃ acts as a Bronsted-Lowry base because it accepts a proton to form NH₄⁺.)
(v) Why ammonia acts as a weak base?
Answer: Ammonia (NH₃) acts as a weak base because it only partially ionizes in water to produce hydroxide ions (OH⁻). The reaction is: NH₃(aq) + H₂O(l) [source symbol unavailable] NH₄⁺(aq) + OH⁻(aq) Since the equilibrium lies to the left, only a small fraction of NH₃ molecules accept protons from water, resulting in a low concentration of OH⁻ and a pH that is not as high as strong bases.
3. Ammonium hydroxide and nitric acid react and produce ammonium nitrate and water. Write balanced chemical equation for this neutralization reaction.
Answer: NH₄OH(aq) + HNO₃(aq) [source symbol unavailable] NH₄NO₃(aq) + H₂O(l)
4. Write balanced chemical equations for the following chemical reactions.
(i) Sulphuric acid + Magnesium hydroxide [source symbol unavailable] magnesium sulphate + water.
Answer: H₂SO₄(aq) + Mg(OH)₂(s) [source symbol unavailable] MgSO₄(aq) + 2H₂O(l)
(ii) Sulphuric acid + Sodium Carbonate [source symbol unavailable] Sodium sulphate + water.
Answer: H₂SO₄(aq) + Na₂CO₃(s) [source symbol unavailable] Na₂SO₄(aq) + H₂O(l) + CO₂(g)
(iii) Hydrochloric acid + Magnesium [source symbol unavailable] Magnesium chloride + water.
Answer: 2HCl(aq) + Mg(s) [source symbol unavailable] MgCl₂(aq) + H₂(g) (Note: This produces hydrogen gas, not water.)
5. Identify Bronsted-Lowry acids or bases in the following reactions.
(i) HNO₃ + H₂O [source symbol unavailable] H₃O⁺ + NO₃⁻
Answer: HNO₃ is the acid (donates H⁺). H₂O is the base (accepts H⁺). H₃O⁺ is the conjugate acid. NO₃⁻ is the conjugate base.
(ii) NH₃ + HNO₃ [source symbol unavailable] NH₄NO₃
Answer: HNO₃ is the acid. NH₃ is the base. NH₄⁺ is the conjugate acid. NO₃⁻ is the conjugate base.
6. Give the Bronsted-Lowry definition of an acid. Write an equation that illustrates the definition.
Answer: A Bronsted-Lowry acid is a substance that donates a proton (H⁺) to another substance.
Equation: HCl(aq) + H₂O(l) [source symbol unavailable] H₃O⁺(aq) + Cl⁻(aq) In this reaction, HCl donates a proton to water, so HCl is the Bronsted-Lowry acid.
7. Identify Bronsted acids and bronsted bases in the following reactions. Classify water as proton donor or proton acceptor.
(i) CH₃COOH(aq) + H₂O [source symbol unavailable] CH₃COO⁻(aq) + H₃O⁺(aq)
Answer: CH₃COOH is the acid. H₂O is the base (proton acceptor).
(ii) HCO₃⁻(aq) + H₂O [source symbol unavailable] CO₃²⁻(aq) + H₃O⁺(aq)
Answer: HCO₃⁻ is the acid. H₂O is the base (proton acceptor).
(iii) NH₃(aq) + H₂O [source symbol unavailable] NH₄⁺(aq) + OH⁻(aq)
Answer: H₂O is the acid (proton donor). NH₃ is the base.
(iv) HCl(aq) + HCO₃⁻(aq) [source symbol unavailable] H₂CO₃(aq) + Cl⁻(aq)
Answer: HCl is the acid. HCO₃⁻ is the base.
(v) HS⁻(aq) + H₂O(l) [source symbol unavailable] S²⁻(aq) + H₃O⁺(aq)
Answer: HS⁻ is the acid. H₂O is the base (proton acceptor).
8. Write equations showing the ionization of the following as Arrhenius acids.
(a) HI(aq)
Answer: HI(aq) [source symbol unavailable] H⁺(aq) + I⁻(aq)
(b) HNO₂(aq)
Answer: HNO₂(aq) [source symbol unavailable] H⁺(aq) + NO₂⁻(aq)
