Acids, bases & salts

An acid forms ${\text{H}}^{+}(aq)$ ions; it is an ${\text{H}}^{+}$ donor. Acids react to form salts:

• acid + metal → salt + hydrogen
• acid + carbonate → salt + water + carbon dioxide
• acid + metal oxide / metal hydroxide → salt + water.

Oxides of non-metals dissolve to give acidic solutions.

Strong acids fully ionise; weak acids only partly. Concentrated/dilute is about how much is dissolved (a separate idea). An acid that donates more than one ${\text{H}}^{+}$ is di-/tri-/polyprotic.

pH measures ${\text{H}}^{+}$ concentration. The scale is logarithmic: a change of 1 pH unit is a ten-fold change in ${\text{H}}^{+}$ concentration, so pH 3 has ten times the ${\text{H}}^{+}$ of pH 4.

A base forms ${\text{OH}}^{-}(aq)$ or accepts ${\text{H}}^{+}$. Metal oxides and hydroxides that dissolve give alkaline solutions. Acid + base → neutralisation, forming a salt and water, and it is usually exothermic:

${\text{H}}^{+}(aq)+{\text{OH}}^{-}(aq)\to {\text{H}}_2\text{O}(l).$

• Confusing strong (fully ionised) with concentrated (lots dissolved).
• Treating the pH scale as linear (each unit is a factor of 10).
• Forgetting that acid + carbonate also releases CO₂.