Question

Calculate the molarity of a solution containing 8g of NaOH in 500 ml of water tomic mass of Na=23, O=16

Answer 1

First let's find out Molar mass of NaOH

Molar mass of NaOH = Mass of Na + Mass of O + Mass of H

⇒ Molar mass of NaOH = 23 + 16 + 1

⇒ Molar mass of NaOH = 40

Now, let's find the number of moles of solute

Number of moles of solute = Mass ÷ Molar mass

⇒ Number of moles of solute = 8 ÷ 40 = 0.2 moles

Volume of solution = 500 mL = 0.5 Litre

For calculating molarity:

Molarity = Number of moles of solute ÷ Volume of solute

⇒ Molarity = 0.2 ÷ 0.5

⇒ Molarity = 0.4 M

∴ Molarity of the solution = 0.4 M

REMEMBER:

Volume of solute should always be in litres.