Question

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

Answer 1

Let the mass of NaOH be x. Since, molarity = number of moles of solute / volume of solution in lit. Hence, 10g of NaOH should be taken to obtain a 0.5 M solution of volume 500 mL.

Answer 2

Solution:

This is a pretty simple question of mole concept and the solution goes like this:

Given:

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 it

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.

MORE INFORMATION:

• A mole is defined as the amount of substance containing the same number of discrete entities (atoms, molecules, ions, etc.) ... Consistent with its definition as an amount unit, 1 mole of any element contains the same number of atoms as 1 mole of any other element.