Theories of acids and bases
4 marks · NormalHydrogen chloride (HCl) and ammonia (NH_3) both undergo acidbase reactions according to the Bronsted-Lowry theory.
Write a balanced equation (with state symbols) for the reaction between aqueous ammonia and hydrochloric acid.
Identify which substance acts as the acid and which acts as the base in this reaction, according to the Bronsted-Lowry theory.
Explain your answer to part (b) in terms of proton transfer.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) NH_3(aq) + HCl(aq) \rightarrow NH_4Cl(aq)
(b) HCl is the acid; NH_3 is the base.
(c) HCl donates a proton (H^+) to NH_3, so HCl is the acid and NH_3 is the base because it accepts the proton.
Common mistakes: Confusing acid and base roles; Omitting state symbols
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correct balanced equation with all state symbols.
B2 (b) · 1 mark · Correct identification of acid and base according to Bronsted-Lowry.
E1 (c) · 1 mark · States that the acid donates a proton and the base accepts a proton.
E2 (c) · 1 mark · Specifies the substances: HCl donates to NH_3, so HCl is acid, NH_3 base.
Worked solution
(a) NH_3(aq) + HCl(aq) \rightarrow NH_4Cl(aq)
(b) According to the Bronsted-Lowry theory, HCl is the acid and NH_3 is the base.
(c) HCl donates a proton (H^+) to NH_3, making HCl the acid. NH_3 accepts the proton, so it is the base.