Question

What is the molarity of a solution prepared with 78.90g of calcium chloride in 750.0 mL of water?

Answer 1

Step 1

Molarity is a type of concentration and it is defined as:

`Molarity\text{ \lparen M or mol/L\rparen = }\frac{Moles\text{ of solute \lparen CaCl2\rparen}}{Volume\text{ of the solution \lparen L\rparen}}\text{ \lparen1\rparen}`

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Step 2

Information provided:

78.90 g calcium chloride (CaCl2)

750.0 mL of water => it is assumed that the volume of water is equal to the volume of solution.

750.0 mL x (1 L/1000 mL) = 0.7500 L

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Information needed:

The molar mass of CaCl2 = 111 g/mol approx. (please, use your periodic table)

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Step 3

Procedure:

Moles of CaCl2 = mass/molar mass = 78.90 g/111 g/mol = 0.710 moles

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Molarity from (1):

Molarity = 0.710 moles/0.7500 L = 0.95 mol/L or M

Answer: Molarity = 0.95 mol/L