Edexcel IAL Chemistry 14.1 Brønsted–Lowry acids and bases

Track a single H⁺ between species, identify the donor and acceptor from their formula change and write water as forming H₃O⁺ rather than free aqueous H⁺.

Exam points

Identify acidic donor hydrogens in carboxylic acid or phenol groups from a structure.
Write HA + H₂O ⇌ H₃O⁺ + A⁻ to show aqueous Brønsted–Lowry acid behaviour.
Classify each reacting species as proton donor or proton acceptor from the equation.

[Maximum number: 3]

The equation for the formation of ammonia in the Haber Process is shown

1 / 2 \mathrm{~N}_{2}(\mathrm{~g})+1 \frac{1}{2} \mathrm{H}_{2}(\mathrm{~g}) \rightleftharpoons \mathrm{NH}_{3}(\mathrm{~g})

(a)

Ammonia from the Haber Process reacts with acids.

With phosphoric acid, $\mathrm{H}_{3} \mathrm{PO}_{4}$ , a number of products are formed in solution. One of these is the fertiliser diammonium hydrogenphosphate.

[ 3 ]

(i)

Write an equation for the production of this fertiliser.

State symbols are not required.

[ 2 ]

formula of diammonium hydrogenphosphate

(1)

- balanced equation

(1)

$\left(\mathrm{NH}_{4}\right)_{2} \mathrm{HPO}_{4}$ $2 \mathrm{NH}_{3}+\mathrm{H}_{3} \mathrm{PO}_{4} \rightarrow\left(\mathrm{NH}_{4}\right)_{2} \mathrm{HPO}_{4}$

Allow multiples

Allow ions for the product

Allow for M2
$\mathrm{NH}_{3}+\mathrm{H}_{3} \mathrm{PO}_{4} \rightarrow\left(\mathrm{NH}_{4}\right) \mathrm{H}_{2} \mathrm{PO}_{4}$

Allow ions for the product

No other TE

Ignore state symbols even if incorrect

(ii)

Write an ionic equation to show that ammonium ions are acidic in aqueous solution.
State symbols are not required.

[ 1 ]

$\mathrm{NH}_{4}^{+} \rightleftharpoons \mathrm{NH}_{3}+\mathrm{H}^{+}$

OR

- $\mathrm{NH}_{4}^{+}+\mathrm{H}_{2} \mathrm{O} \rightleftharpoons \mathrm{NH}_{3}+\mathrm{H}_{3} \mathrm{O}^{+}$

Allow → instead of ⇌

Do not award reactions reversed

Allow
$\begin{aligned} & \mathrm{NH}_{4}^{+}+\mathrm{OH}^{-} \rightarrow \mathrm{NH}_{3}+\mathrm{H}_{2} \mathrm{O} & \text { Allow } \rightleftharpoons \text { instead of } \rightarrow \end{aligned}$

Ignore state symbols even if incorrect

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14.1—A Brønsted–Lowry acid is a proton donor and a Brønsted–Lowry base is a proton acceptor and that acid-base reactions involve question 1

Question (a)

Question (i)

Question (ii)