Proton transfer reactions

A **proton (H⁺) donor**.

A **proton (H⁺) acceptor**.

A **hydrogen ion, H⁺** — a hydrogen atom that has lost its electron.

Two species that differ by **exactly one H⁺** (an acid and the base left after it donates).

**Remove** one H⁺ from the acid (e.g. HCl → Cl⁻).

**Add** one H⁺ to the base (e.g. NH_{3} → NH_{4}^{+}).

A species that can **both donate and accept** a proton (e.g. H_{2}O, HCO_{3}⁻).

**HSO_{4}⁻** (remove one H⁺ — not SO_{4}^{2-}, which is two H⁺ away).

**H_{3}O^{+}** (the oxonium / hydronium ion).

**H_{2}O** and **HCO_{3}⁻** — both can donate or accept a proton.

**HCl** — it donates the proton; water is the base.

An acid can only **donate** H⁺ if a base is there to **accept** it — every proton transfer has both.

A measure of acidity based on hydrogen-ion concentration: $\text{pH} = -\log_{10}[\text{H}^{+}]$.

$\text{pH} = -\log_{10}[\text{H}^{+}]$ — given in the data booklet.

$[\text{H}^{+}] = 10^{-\text{pH}}$ — the rearranged given equation.

The ionic product of water, $K_{w} = [\text{H}^{+}][\text{OH}^{-}] = 1.0\times10^{-14}$ at 25 °C.

pH < 7 acidic · pH = 7 neutral · pH > 7 basic (alkaline), at 25 °C.

[H_{+}] changes by a factor of **10** (pH is a log scale).

Strong = **fully** dissociated into ions; weak = only **partially** dissociated.

No — strength is the **degree of dissociation**; concentration is the amount dissolved.

Single arrow, e.g. $\text{HCl} \rightarrow \text{H}^{+} + \text{Cl}^{-}$ (full dissociation).

Equilibrium arrows, e.g. $\text{CH}_{3}\text{COOH} \rightleftharpoons \text{H}^{+} + \text{CH}_{3}\text{COO}^{-}$ (partial).

Strong acid has a **lower pH**, **higher conductivity** and a **faster** reaction (more H_{+} ions).

It is fully dissociated, so it gives a **higher [H_{+}]**, and a higher [H_{+}] means a lower pH.

The reaction of an **acid with a base** to give a **salt and water**; the H⁺ and OH⁻ cancel out.

The ionic compound formed when the **H⁺** of an acid is replaced by a **metal ion** (or NH_{4}⁺).

**salt + hydrogen** (e.g. Mg + 2HCl → MgCl_{2} + H_{2}).

**salt + water** (neutralisation; the base is a metal oxide or hydroxide).

**salt + water + carbon dioxide** (e.g. 2HCl + CaCO_{3} → CaCl_{2} + H_{2}O + CO_{2}).

A **chloride** (e.g. NaCl, MgCl_{2}).

A **sulfate** (e.g. Na_{2}SO_{4}, MgSO_{4}).

A **nitrate** (e.g. NaNO_{3}, Ca(NO_{3})_{2}).

**Hydrogen** gives a squeaky **'pop'** with a lit splint.

**Carbon dioxide** turns **limewater milky** (cloudy).

It is **diprotic** — it provides **two H⁺**, so it neutralises two 1+ bases: 2NaOH + H_{2}SO_{4} → Na_{2}SO_{4} + 2H_{2}O.

Balance the **ionic charges** (e.g. Mg²⁺ with Cl⁻ → MgCl_{2}), then balance the whole equation.