Question

The molecular weight of anhydrous calcium chloride is 110.99. How many grams do you need for 100 ml of 50 mm calcium chloride?

Answer 1

You have the volume and molarity of CaCl2 required. You need to first calculate the number of moles of calcium chloride. 

No. of moles of CaCl2 required = 0.1L x 5mM (or 5 mmol/L) = 0.5 mmol (or 0.0005 mol) 

Given the molecular weight, the amount of anhydrous calcium chloride to weigh out is thus: 

110.99 g/mol x 0.0005mol = 0.55495g approx. 0.555g 

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No. of moles (mol) = vol (L) x concentration (M) 

Mass (g) = relative atomic/molecular weight (g/mol) x no. of moles (mol)