Answer:
0.076 g
Step-by-step explanation:
First obtain the hydroxide ion concentration from the pH of the solution;
Recall that pH+ pOH= 14
Therefore;
pOH= 14-pH
pOH=14-12.28
pOH= 1.72
Since;
pOH= -log[OH^-]
[OH^-] = Antilog (-pOH)
[OH^-] = Antilog (-1.72)
[OH^-] = 0.019055 M
Note that
[Na^+]=[OH^-]= [NaOH]= 0.019055 M
But;
n= CV
Where;
n= number of moles given by mass/ molar mass
C= concentration of solution
V= volume of solution
mass of NaOH= the unknown
Molar mass of NaOH= 40gmol-1
Let the mass of NaOH be m
Hence;
m/40= 0.019055 × 100/1000
m/40= 1.9055×10^-3
m= 1.9055×10^-3 ×40
m= 0.076 g