What is $pH$ for a solution prepared from a $5.7g$ mass of sodium hydroxide that is dissolved in a $100mL$ volume of water?

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Answer 1 · 2016-09-30T17:46:27

$pH$ is exceptionally high; $pOH$ is negative.

$[NaOH]$ $=$ $(5.7*g)/(40.00*g*mol^-1)$ $=$ $0.143*mol$ . And thus $[HO^-]$ $=$ $(0.143*mol)/(0.100*L)$ $=$ $1.43*mol*L^-1$ .

Since sodium hydroxide gives quantitative hydroxide ion in aqueous solution, $[HO^-]=1.43*mol*L^-1$ .

Now $pOH$ $=$ $-log_10[HO^-]$ $=$ $-log_10(1.43)$ $=$ $-0.154$ ; this is an exceptionally high concentration of hydroxide ion.

Now $pH+pOH=14$ (by definition; see here for the derivation, thus $pH$ $=$ $14-pOH$ $=$ $14.15$

What is pHpH for a solution prepared from a 5.7*g5.7*g mass of sodium hydroxide that is dissolved in a 100*mL100*mL volume of water?