Theories of acids and bases
4 marks · NormalThe table below shows five example reactions. For each reaction, state which theory (Arrhenius, Bronsted-Lowry, or both) can be used to explain it, and give a reason for your choice.
| Equation | Theory (Arrhenius / Bronsted-Lowry / Both) | Reason |
|---|---|---|
| HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) | ||
| HCl(g) + NH3(g) → NH4Cl(s) | ||
| HNO3(aq) + NH3(aq) → NH4NO3(aq) | ||
| H2O(l) + NH3(g) → NH4^+(aq) + OH^-(aq) | ||
| NH4^+(aq) + OH^-(aq) → NH3(aq) + H2O(l) |
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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Common mistakes: Saying Arrhenius applies to non-aqueous reactions
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Marking points
B1 · 2 marks · Two marks for correctly assigning the correct theory (Arrhenius / Bronsted-Lowry / Both) for each reaction (one mark for every two correct assignments, maximum 2 marks).
E1 · 2 marks · Two marks for giving at least two correct and relevant reasons corresponding to the correct theory assignments.
Worked solution
| Equation | Theory | Reason |
|---|---|---|
| HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) | Both | Both take place in aqueous solution, HCl and NaOH fit both theories. |
| HCl(g) + NH3(g) → NH4Cl(s) | Bronsted-Lowry | No water present; Arrhenius doesn't apply, but there is a proton transfer. |
| HNO3(aq) + NH3(aq) → NH4NO3(aq) | Bronsted-Lowry | Ammonia is not OH^-, so Arrhenius doesn't apply; proton transfer does occur. |
| H2O(l) + NH3(g) → NH4^+(aq) + OH^-(aq) | Bronsted-Lowry | Water acts as acid, ammonia as base; not Arrhenius as it's not acid + OH^-. |
| NH4^+(aq) + OH^-(aq) → NH3(aq) + H2O(l) | Both | Aqueous solution, OH^- and acid present. |