Assuming equal concentrations, arrange these solutions by pH.

NH3 (aq)

Sr (OH) 2 (aq)

HBr (aq)

HCN (aq)

KOH (aq)

Highest pH (most basic)

Sr (OH) 2 (aq)

KOH (aq)

NH3 (aq)

HF (aq)

HClO4 (aq)

Lowest pH (most acidic)

Explanation:

The concentration of H + ion will determine the pH of a solution. The pH actually reflects the ratio of H + ion and OH - since both of them can combine into water. Solution with more H + ion will have a lower pH and called acidic, while more OH - will have high pH and be called basic. Strong acid/base will be ionized more than weak acid/base.

Sr (OH) 2 (aq) = strong base, release 2 OH - ion per mole

KOH (aq) = Strong base, release 1 OH - per mole

NH3 (aq) = weak base, release less than 1 OH - per mole

HF (aq) = strong acid, release 1 H + per mole

HClO4 (aq) = stronger acid, release 1 H + per mole