Question

Calculate the molarity of the following solutions.

a) 0.950 mol of Na2S in 1.85 L of solution.

___M

b) 30.9 g of MgS in 833 mL of solution.

___M

Answer 1

Answer – a) given, moles of Na₂S = 0.950 moles

Volume = 1.85 L

We know,

Molarity of Na₂S = moles / L

                            = 0.950 moles / 1.85 L

                            = 0.514 M

b) Given, mass of MgS = 30.9 g , volume = 833 mL

We need to convert the mass , g to mole

We know formula,

Moles = given mass / molar mass

         = 30.9g / 56.371 g.mol^-1

        = 0.548 moles

Now convert the given volume mL to L

We know

1 mL = 0.001 L

So, 833 mL = ?

= 0.833 L

We know,

Molarity of MgS = moles / L

                            = 0.548 moles / 0.833 L

                            = 0.658 M