# Which of the following solutions at equimolar solution would give the LOWEST pH?

## $\left(a\right)$ $\text{acetonitrile;}$ $\left(b\right)$ $\text{calcium hydroxide;}$ $\left(c\right)$ $\text{potasium hydroxide;}$ $\left(d\right)$ $\text{hydroiodic acid;}$ $\left(e\right)$ $\text{ammonia.}$

##### 1 Answer
Nov 1, 2016

Ca(OH)_2; KOH; NH_3; HC-=N; HI

#### Explanation:

Hydrogen iodide is definitely the strongest acid in aqueous solution, and thus will give the lowest $p H$.

Hydrocyanic acid is a fairly weak Bronsted acid, but still the $p H$ will be well below $7$:

$H - C \equiv N + {H}_{2} O r i g h t \le f t h a r p \infty n s {H}_{3} {O}^{+} + N \equiv {C}^{-}$

Next cab off the rank is ammonia, which is a weak base in aqueous solution:

$N {H}_{3} \left(a q\right) + {H}_{2} O r i g h t \le f t h a r p \infty n s N {H}_{4}^{+} + H {O}^{-}$

$K O H$ and $C a {\left(O H\right)}_{2}$ are strong Bronsted bases, and will dissolve to give quantitative hydroxide ion. Since, you specified equal concentrations, calcium hydroxide delivers 2 equiv hydroxide anion, and will thus give the most basic solution, with the highest value of $p H$.