Calculate the amount of a substance that is 120 g of sodium hydroxide.

given:
m(NаОН) = 120 g
find:
ν(NаОН)  - ?
Solution:
ν= m/( М).
М(NаОН) = 23 + 16 + 1  = 40 g/ mol
ν(NаОН)= (m(NаОН))/(М(NаОН))= (120 g)/(40 g/mol)=3  mol
Answer:ν(NаОН) =3 mol.