H⁺ meets OH⁻

The idea

Since acids give H+(aq) and bases give OH–(aq), neutralisation is H+(aq) + OH–(aq) → H2O(l), while the acid's anion and the base's cation form the salt (HX + MOH → MX + HOH).

Mix an acid and a base

HCl gives H⁺ and Cl⁻. NaOH gives Na⁺ and OH⁻. Pour them together.

Which two ions join to make water?

• H⁺ and OH⁻
• Na⁺ and Cl⁻
• H⁺ and Na⁺

Join the ions

Tap one H⁺, then one OH⁻. They join into water. Do it for all three pairs.

The ions left over are the salt

Acids give H⁺(aq) and bases give OH⁻(aq). So neutralisation is H⁺(aq) + OH⁻(aq) → H₂O(l). The acid's anion and the base's cation make the salt.

Na⁺ and Cl⁻ were already in the beaker. They did not change. They just stay as the salt.

• Acid | Base | Salt | Water
• HX | MOH | MX | HOH
• HCl | NaOH | NaCl | H₂O

Notes

Since acids give H⁺(aq) and bases give OH⁻(aq), neutralisation is H⁺(aq) + OH⁻(aq) → H₂O(l), while the acid's anion and the base's cation form the salt (HX + MOH → MX + HOH).

Check yourself

In neutralisation, which two ions join?

HNO₃ + NaOH → ? + H₂O. What is the salt?

HCl + KOH → ? + H₂O. What is the salt?

In HX + MOH → MX + HOH, what is HOH?

• Na⁺ and Cl⁻. They are left over as the salt.
• H⁺ and OH⁻ — correct. Yes! They make H₂O.
• H⁺ and Cl⁻. Cl⁻ is the acid's own partner. It stays as part of the salt.
• NaOH. That is the base we started with.
• HNO₃. That is the acid we started with.
• NaNO₃ — correct. Yes! The acid's anion (NO₃⁻) and the base's cation (Na⁺).
• KCl — correct. Yes! K⁺ from the base and Cl⁻ from the acid.
• KOH. That is the base we started with.
• HCl. That is the acid we started with.
• The salt. The salt is MX.
• Water (H₂O) — correct. Yes! HOH is just H₂O written with the H and OH apart.
• The acid. The acid is HX.