Answers to Practice Problems – Introduction to Moles and Molarity

1. How many grams of MgCl₂ are there in 1 Millimole (mmol) of MgCl₂?

Atomic wt. of Mg = 24; atomic wt. of Cl = 35.

Formula wt. of MgCl₂ = (1 x 24) + (2 x 35) = 94

94 g MgCl₂ X 1 mol____ = 0.094 g / mmol MgCl₂= 94 mg / mmol MgCl₂

1 mol MgCl₂ 1,000 mmol

2. You want to make a 1.5 mmol solution of NaCl. How would you do it?

FW NaCl = 58. 1.5 mol NaCl = 58 g/mol

58 g NaCl X 1 mol____ = 0.058 g / mmol NaCl = 58 mg / mmol NaCl

1 mol NaCl 1,000 mmol