A chemist prepares a solution by adding 424 mg of CoCl2 (MW = 129.84 g/mol) to a volumetric flask, and then adding water until the total volume of the contents of the flask reaches the calibration line that indicates 500 mL. Determine the molarity of the prepared solution.

0.00654 M

Explanation:

1) dа ta:

a) mass = 422 mg

b) MW = 129.84 g/mol

c) V = 500 ml

d) M = ?

2) Chemical principles and formulae:

a) Molarity a the unit of concentration that measures the number of moles of solute per liter of solution:

M = number of moles of solute / V in liter

b) The number of moles may be calculated by this formula:

number of moles = mass in grams / molar mass

3) Calculations:

a) Unit conversions

mass in grams = 424 mg * 1 g / 1,000 mg = 0.424 g

Volume in liters = 500 ml * 1 liter / 1,000 ml = 0.500 ml

b) Number of moles of solute, n:

n = mass in grams / molar mass = 0.424 g / 129.84 g / mol = 0.00327 mol

c) Molarity, M:

M = n / V in liters = 0.00327 mol / 0.500 liter = 0.00654 M ← answer