solutions chemistry

Question

Answer the following questions about a 15.0 mL CuCl2·2H2O solution that has a 0.125 M

concentration.

A. How many grams of CuCl2·2H2O are present in this solution? (5)

mass of CuCl2·2H2O (g): _______________

B. What would be the new concentration of the solution if it was diluted to 65.0 mL?

Answer 1

Question A:

15.0 ml = 0.015 liters

0.125 M = 0.125 moles/liter

The number of moles of CuCl2·2H2O = (0.125 moles/liter)(0.015 liters) = 0.001875 moles

Calculate molar mass:

Cu: (1)(63.546) = 63.546 g/mol

Cl: (2)(35.453) = 70.906 g/mol

H: (4)(1.008) = 4.032 g/mol

O: (2)(15.999) = 31.998 g/mol

Total = 170.482 g/mol

The number of grams of CuCl2·2H2O = (0.001875 moles)(170.482 g/mol) = 0.3197 g round the answer to 0.320 since there are 3 sig figs in the givens

Question B:

Since there were 0.001875 moles of CuCl2·2H2O that quantity of molecules stays there but now you have more solvent. If it was diluted to 65 ml, the new concentration is 0.001875 moles/0.065 liters = 0.028846 M but rounding to 3 sig figs gives you 0.0288 M