A solution is made by dissolving 328 g of NaOH in approximat

A solution is made by dissolving 32.8 g of NaOH in approximately 450 mL of water in a volumetric flask. The solution becomes quite warm, but after it is allowed to return to room temperature, water is added to total 500 mL of solution. Calculate the pH of the final solution. Report pH to 2 decimal places

Solution

First find the final concentration of NaOH

Molar mass of NaOH,
MM = 1*MM(Na) + 1*MM(O) + 1*MM(H)
= 1*22.99 + 1*16.0 + 1*1.008
= 39.998 g/mol


mass(NaOH)= 32.8 g

use:
number of mol of NaOH,
n = mass of NaOH/molar mass of NaOH
=(32.8 g)/(39.998 g/mol)
= 0.82 mol
volume , V = 500 mL
= 0.5 L


use:
Molarity,
M = number of mol / volume in L
= 0.82/0.5
= 1.64 M

so,
[NaOH] = 1.64 M

use:
pOH = -log [OH-]
= -log (1.64)
= -0.2148


use:
PH = 14 - pOH
= 14 - -0.2148
= 14.2148
Answer: 14.21