Concentration of Solutions

Spring Semester, 2013Mrs. L. Fox

ConcentrationThe amount of a dissolved substance

occupying a given volume of the solution

Dilute SolutionsContain few solute molecules

Concentrated SolutionsContain many solute molecules

MolarityThe number of moles of solute dissolved in 1

liter of solutionSymbol is MUnits are mol/LA solution that is 0.75 M KCl

Contains 0.75 mols of KCl in every liter

Make 1 liter of a 0.75 M solution of KClCalculate the molar mass of KCl

1 mol K = 39.10 g/mol1 mol Cl = 35.45 g/mol1 mol KCl = 39.10 + 35.45 = 74.55 gKCl/mol

Convert the molarity to the sample mass required

0.75 M KCl = 0.75 molsKCl/L * 74.55 g/mol

= 55.91 gKCl/L

You need to add 55.91 g of KCl to 1 liter of water to make 0.75 M KCl solution

What if you want a smaller amount?

To make 150 mL

55.91 g/L * 1 L/1000 mL * 150 mL

= 8.39 gKCl

Molarity CalculationsM = # mol solute/# L solution

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What is the molarity of a bleach solution containing 9.5 g of NaOCl per liter of bleach?

Calculate the molarity of 1.60 L of a solution containing 1.55 g of dissolved KBr.

Diluting Stock SolutionsSometimes, the molarity of a solution is not

what you wantYou have to dilute the solution to get the

molarity you do wantFor that, you use

M1V1 = M2V2 (In Chem Reference Sheet)

What volume would you use to make 0.50 L of 0.300 M CaCl2 solution?

21) What volume of a 3.00 M KI solution would make 0.300 L of a 1.25 M solution?

How many mL of 5.0M solution to prepare 100.0mL of 0.25 M H2SO4?