Strong and weak acids

In a nutshell

Strong acids fully dissociate and weak acids partially dissociate. Strong and weak acids can both be either strong or concentrated.

Acids release protons into water

Acids are ionised in solution and they release $H^{+}$ ions into solution.

Examples

$hydrochloric\ acid\ \rightarrow hydrogen\ ion \ +\ chloride\ ion \\ \ \\HCl \rightarrow H^+ + Cl^-$

$sulphuric\ acid\ \rightarrow\ hydrogen\ ion\ +\ hydrogen\ sulphate\ ion \newline \ \\ H_{2}SO_{4} \rightarrow H^+ + HSO_{4}^-$

Strong acids

Definition

Strong acids fully dissociate in water to produce the maximum number of $H^{+}$ ions.

Example

An example of a strong acid is hydrochloric acid $(HCl)$ . It fully dissociates into $H^{+}$  and $Cl^{-}$  ions.

$hydrochloric\ acid\ \rightarrow\ hydrogen \ ion\ +\ chloride\ ion\newline \ \\ HCl \rightarrow H^+ + Cl^-$ 

Weak acids

Definition

Weak acids, such as acetic acid ( $CH_{3}COOH$ ), only partially dissociate. Some of the molecules will dissociate whilst most will not, therefore not contributing to the acidity of the solution.

Example

An example of a weak acid is acetic acid ( $CH_{3}COOH$ ). It partially dissociates into $H^{+}$ and $CH_{3}COO^{-}$ ions.

$acetic\ acid\ \rightleftharpoons\ hydrogen\ ion\ +\ acetate\ ion\newline \ \\ CH_{3}COOH \rightleftharpoons\ H^+\ + CH_{3}COO^-$

Chemistry; Chemical changes; KS4 Year 10; Strong and weak acids - Higher

1.	Strong acid (complete dissociation)
2.	Weak acid (partial dissociation)

pH of acids

pH is a measure of the $H^+$ ion concentration in solution. For a decrease of one on the pH scale, there is a $10$ times increase in $H^+$ ion concentration and vice versa for an increase in pH.

Examples

A solution with a pH of $3$ has a $H^+$ concentration that is $10$ times greater than a solution with a pH of $4$ and $100$ times greater than a solution with a pH of $5$ .
If the pH of a solution drops from $14$ to $10$ , the difference is $4$ so the concentration of $H^+$ ions is $10^4$ greater.

Concentrated and dilute acids

Concentrated and strong acids are not the same thing. Concentration refers to the amount of acid which is present in a particular volume of water.

The greater amount of acid in a given volume of water, the more concentrated the solution. As acid concentration increases, the pH will decrease regardless of whether the acid is strong or weak.