Question

Four different solutions (I, II, III, and IV) are labeled on the pH scale below.

A p H scale is shown, fading from red at the left end to blue at the right. p H is shown in even increments from 0 to 14. Points marked are: Roman numeral 1 at 1 on the scale, Roman 2 at 6, Roman 3 at 11, and roman 4 at 13.

Why would solution IV be considered the most concentrated base out of the four substances?

Answer 1

Because IV has the highest pH (13), it has the lowest H+ concentration and the highest OH− concentration. At 25 °C pH + pOH = 14, so for IV pOH = 1 and [OH−] = 10^(−1) = 0.1 M. That is larger than the [OH−] for the other solutions (for example pH 11 → [OH−] = 10^(−3) M), so IV is the most concentrated base.