Theories of acids and bases
5 marks · HardEthanoic acid (CH_3COOH) reacts with ammonia (NH_3) in aqueous solution to form ammonium ethanoate (CH_3COONH_4).
Use the Bronsted-Lowry theory to explain this reaction.
Write a balanced equation for this reaction, including state symbols.
Identify the Bronsted-Lowry acid and base among the reactants, and state which substance donates a proton.
Explain, using the concept of proton transfer, how the products are formed according to the Bronsted-Lowry theory.
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.
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(a) CH_3COOH(aq) + NH_3(aq) \rightarrow CH_3COO^- (aq) + NH_4^+ (aq)
(b) Acid: CH_3COOH (ethanoic acid), Base: NH_3 (ammonia); CH_3COOH donates a proton to NH_3.
(c) CH_3COOH donates a proton (H^+) to NH_3, forming CH_3COO^- and NH_4^+. This is an acid–base reaction by Bronsted-Lowry as it involves proton transfer from the acid (ethanoic acid) to the base (ammonia).
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Marking points
A1 (a) · 1 mark · Correct balanced equation with state symbols.
B1 (b) · 1 mark · Correct identification of acid and base among reactants: CH_3COOH is the acid, NH_3 is the base.
B2 (b) · 1 mark · States correctly that ethanoic acid donates a proton to ammonia.
C1 (c) · 1 mark · Explains proton transfer concept: acid donates H^+ to base.
C2 (c) · 1 mark · Relates formation of CH_3COO^- and NH_4^+ to proton transfer between reactants.
Worked solution
a) The balanced equation is:
b) According to the Bronsted-Lowry theory, CH_3COOH acts as the acid because it donates a proton to NH_3, which acts as the base (proton acceptor).
c) The acid (CH_3COOH) transfers a proton (H^+) to the base (NH_3). CH_3COOH loses a proton to form CH_3COO^-, and NH_3 gains a proton to form NH_4^+. This is explained as a proton transfer reaction according to the Bronsted-Lowry theory.