Calculate Molarity

Question

Calculate the molarity of 0.400 mol of Na2S in 1.75 L of solution.

 

Calculate the molarity of 24.1 g of MgS in 861 mL of solution.

Answer 1

Molarity = moles/Liters

 

For Na2S:

Molarity = 0.400 moles/1.75 L

             = 0.229 M

 

For MgS, we have to first convert the mass given into moles by dividing by the molar mass, and the volume to liters. Then we can substitute everything into the molarity equation as before:

24.1 g MgS x (1 moles/56.38g) = 0.427 moles MgS

861mL X (1 L/1000mL) = 0.861 L

 

Molarity = moles/Liters

             = 0.427 moles/0.861 L

             = 0.496 M