Question

Calculate the molarity of the following solutions.

a) 0.200 mol of Na2S in 1.20 L of solution.

b) 24.7 g of MgS in 993 mL of solution.

Answer 1

a)

number of moles = 0.2 mol

Volume = 1.2 L

Molarity = number of moles/ volume

            = 0.2 /1.2

            =0.167 M

b)

molar mass of MgS = 24.3+32 = 56.3 gm

mass= 24.7gm

number of moles = mass/molar mass = 24.7/56.3 = 0.439 mol

Volume = 993 mL = 0.993 L

Molarity = number of moles/volume

            = 0.439/0.993

            =0.442 M