Question

Calculate the mass of NaOH required to make 500ml of 0.5 molar aqueous solution. (molar mass of NaOH is 40)
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Answer 1

Volume of NaOH = 500 mL

Molarity of the aqueous solution = 0.5 M

Molar mass of NaOH= (23+16+1)g = 40g

Let the mass of NaOH be x.

Now , according to formula number of moles of a given substance = given mass/molar mass

Therefore, no. Of moles of NaOH= x/40

Since, molarity = number of moles of solute/ volume of solution in lit.

Hence, 0.5 = (x/40)/(500/1000)

Solving this we get x= 10g

Hence, 10g of NaOH should be taken to obtain a 0.5 M solution of volume 500 mL.

Answer 2

Explanation:

Morality = no. of moles of solute / volume in liter

moles = molarity × volume

moles = 0.5 × 1/2

moles = 0.25

moles = given mass / molar mass

moles × molar mass = given mass

0.25 × 40 = mass

mass = 10 g