Question

A solution NaOH(aq) contains 5.7 g NaOH(s) per 100.0 mL of solution Calculate the pH and the pOH of the solution at 25°C pH РОН %3

Answer 1

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)= 5.7 g

use:

number of mol of NaOH,

n = mass of NaOH/molar mass of NaOH

=(5.7 g)/(40 g/mol)

= 0.1425 mol

volume , V = 1*10^2 mL

= 0.1 L

use:

Molarity,

M = number of mol / volume in L

= 0.1425/0.1

= 1.425 M

So,

[NaOH] = 1.425 M

So,

[OH-] = 1.425 M

use:

pOH = -log [OH-]

= -log (1.425)

= -0.1538

use:

PH = 14 - pOH

= 14 - -0.1538

= 14.1538

Answer:

pH = 14.15

pOH = -0.154