Calculate weight, concentration and pH of solution

Calculate the NaOH weight required to prepare 500ml of NaOH solution of pH=13. Room temperature is 250C.

Calculate concentration of solution of known pH

Calculate pOH from pH by using the pH + pOH = 14 (at 250C)
Then you can calculate the concentration of NaOH solution by pOH = -log10[OH-(aq)] .
Then find the required moles of NaOH by the equation of C =n/v . Here C = concentration, n=required moles, v = volume of solution
Now weight is measured by multiplying number of moles and molar mass.


Assumptions

The OH- received from water dissociation is negligible when it compares with OH- received from NaOH.


calculate weight concentration of solution

Calculate pOH from pH value

pH + pOH = 14
13 + pOH = 14
pOH = 1


Calculate concentration (in mol dm-3) of solution

Now we know the pOH of NaOH solution. Use the relation of pOH and OH- concentration to calculate the concentration of OH-.

pOH = -log10[OH-(aq)]
1 = -log10[OH-(aq)]
[OH-(aq)] = 0.1 mol dm-3


Find the required moles of NaOH

Concentration, moles amount, and volume relation is used.

C = n/v
0.1 = n/0.5      [500 ml = 0.5 dm3]
n = 0.05mol

NaOH amount = 0.05 mol


Find the required weight(g)

Multiply required moles times molecular weight

m = mass
n = moles
M = molecular weight
n = m/M

m = molecular weight * moles
m = M*n
m = 0.05 * 40
m = 2g

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