Question

5.0 g of sodium hydroxide (molar mass 40 g mol^-1) is dissolved in little quantity of water and the solution is diluted upto 100 mL. What is the molarity of the resulting solution?

Options

• 0.1 mol dm^-3

• 1.0 mol dm^-3 

• 0.125 mol dm^-3 

• 1.25 mol dm^-3

Answer 1

1.25 mol dm^-3 

Explanation:

Given, W (mass of solute) = 5.0 g
m (molar mass of solute) = 40 g mol^-1
Volume = 100 mL

Molarity is given as,

M = `"Moles of solute"/("Volume of solution" ("in L"))`

M = `("W" xx 1000)/("m" xx "Volume of solution" ("in mL"))`

M = `(5.0 " g" xx 1000)/(40 xx 100)`

M = 1.25 mol dm^-3