Question

You have a solution of 250 mL of .150 M solution of cobalt(II) chloride. Using this solution, how would you prepare 100 mL of a .600 M solution?

Answer 1

solution of 250 mL of .150 M solution of cobalt(II) chloride

Moles of cobalt(II) chloride = molarity x volume

= 0.150 moles/L x 0.250 L

= 0.0375 moles

Mass of cobalt(II) chloride = moles x molecular weight

= 0.0375 mol x 129.839 g/mol

= 4.87 g

Now prepare 100 mL of a .600 M solution

Moles of cobalt(II) chloride = molarity x volume

= 0.600 moles/L x 0.100 L

= 0.0600 moles

Mass of cobalt(II) chloride = moles x molecular weight

= 0.0600 mol x 129.839 g/mol

= 7.79 g

Difference of mass between two solutions = 7.79 - 4.87

= 2.92 g

Therefore add 2.92 g of cobalt(II) chloride in the 250 mL of 0.150 M solution.

After adding it will become 100 mL of a 0.600 M solution.