Question

When 4g of naoh is dissolved in 10l of water the ph is?

Answer 1

Number of moles of NaOH = mass/molar mass = 4g / 40g/mol = 0.1mol
Molarity of NaOH = moles/volume in litres
  = 0.1mol/10L = 10-2 M
Now,
[OH-] = [NaOH] =  10-2
[H+] = Kw/[OH-]
  =10-14/10-2
    = 10-12
pH = -log [H+]
  = -log [10-12]
  = 12

Answer 2

Answer : The pH is, 12

Solution : Given,

Mass of NaOH = 4 g

Molar mass of NaOH = 40 g/mole

Volume of solution = 10 L

First we have to calculate the concentration of hydroxide ion.

$\text{Concentration of }NaOH=\frac{\text{Mass of }NaOH}{\text{Molar mass of }NaOH\times \text{Volume of solution in liters}}=\frac{4g}{40g/mole\times 10L}=0.01M$

The concentration of NaOH is, 0.01 M that means the concentration of sodium ion and hydroxide ion is equal to 0.01 M

Now we have to calculate the pOH.

$pOH=-\log [OH^-]$

$pOH=-\log (0.01)$

$pOH=2$

Now we have to calculate the pH.

$pH+pOH=14$

$pH+2=14$

$pH=12$

Therefore, the pH is, 12