Question

Calculate the molarity of a solution that contains 20.0 grams of sodium hydroxide in a 200ml solution.

Answer 1

given mass = 20 g
molar mass = 40 g

volume(in litres) = 200/1000 litr.

Molarity = given mass / molar mass // Volume(in litreS)

Molarity = 2.5M

Answer 2

Molarity is defined as moles of solute, here is sodium hydroxide, NaOH, divided by liters of solution.

molarity=moles of solute/liters of solution.

Now, molar mass of sodium hydroxide is 40 gm.

Therefore,

20g*1 mole NaOH/40.0g=0.5 mol NaOH.

Now, the volume of the solution in liters will be

200mL⋅1 L/1000mL=0.2 L

Therefore, the molarity of the solution will be

c=n/V

c=0.5 moles/0.2 L

=2.5 M.

Thus, the molarity of a solution that contains 20.0 grams of sodium hydroxide in a 200ml solution is 2.5 M.