Neutralization and titration: write neutralization reactions that form a salt and water, and use titration data to find an unknown concentration.

What this topic is asking

Standard CH.5 finishes with neutralization and titration. Virginia expects you to write a neutralization reaction (acid plus base gives a salt and water) and to use titration data to find an unknown concentration. Titration is a classic laboratory skill, so the SOL often frames these as data-based or lab items.

Neutralization

For example, $\text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O}$ and $\text{H}_2\text{SO}_4 + 2\,\text{KOH} \rightarrow \text{K}_2\text{SO}_4 + 2\,\text{H}_2\text{O}$. Neutralization is a kind of double replacement, and the salt formed depends on which acid and base react. When exactly enough base has been added to react with all the acid, the solution is neutralized.

Titration

The known titrant is added until the indicator changes color, marking that the moles of acid and base have reacted in the ratio of the balanced equation. The measured volumes and the known concentration then give the unknown concentration. Reading the buret accurately and stopping at the first lasting color change are the key practical skills.

The titration calculation

For a reaction with a $1 : 1$ mole ratio of acid to base (such as $\text{HCl}$ with $\text{NaOH}$), the moles of acid equal the moles of base at the equivalence point, so:

Here $M$ is molarity and $V$ is volume; because the volumes appear as a ratio, they can both stay in milliliters. If the mole ratio is not $1 : 1$ (for example a diprotic acid like $\text{H}_2\text{SO}_4$ with $\text{NaOH}$, a $1 : 2$ ratio), find the moles of the known solution first, apply the mole ratio, then divide by the unknown volume.

Try this

Q1. Write the products of the neutralization $\text{HNO}_3 + \text{KOH} \rightarrow$ ?. [1 point]

• Cue. A salt and water: $\text{KNO}_3 + \text{H}_2\text{O}$.

Q2. In a $1 : 1$ titration, $30.0$ mL of $0.20$ M base neutralizes $15.0$ mL of acid. Find the acid molarity. [2 points]

• Cue. $M_a = \dfrac{(0.20)(30.0)}{15.0} = 0.40$ M.