# 13.3 Concentration,Molarity and Molality

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### 13.3 Concentration of Solutions:

13.3 Concentration of Solutions

### PowerPoint Presentation:

The concentration of a solution is a measure of the amount of solute in a given amount of solvent or solution

### Molarity:

Molarity Molarity (M) is the number of moles of solute in one liter of solution. Molarity(M) = amount of solute (mol) volume of solution (L ) **pay close attention to the units involved in this calculation. If the given is not in moles and liters, you will have to convert before you plug into the equation.

### Molarity Example #1:

Molarity Example #1 You have 3.50 L of a solution that contains 90.0 g of sodium chloride, NaCl . What is the molarity of that solution? 90.0 g NaCl 1 mol NaCl = 1.54 mol NaCl 58.44 g NaCl M = mol solute 1.54 mol NaCl = .440 M NaCl L solution 3.50 L

### Molarity example #2:

Molarity example #2 You have .8 L of a .5 M HCl solution. How many moles of HCl does this solution contain? M = mol solute .5 M HCl = X mol L solution .8 L = .4 mol HCl

### Molality:

Molality Molality (m) is the concentration of a solution expressed in moles of solute per kilogram of solvent. m = moles solute mass of solvent (kg ) ** remember to convert to moles and kg if necessary

### Molality example :

Molality example A solution was prepared by dissolving 29.8 g of sucrose (C 12 H 22 O 11 ) in 125 g of water. Find the molal concentration of this solution. m = moles solute mass of solvent (kg) 29.8 g C 12 H 22 O 11 mol C 12 H 22 O 11 = .0870 mol C 12 H 22 O 11 342.34 g C 12 H 22 O 11 m = .0870 mol = .696 m C 12 H 22 O 11 .125 kg

### Diluting Solutions:

Diluting Solutions Not all compounds are in the solid form. Acids are purchased as liquids (“stock solutions”). Yet, we still need a way to make molar solutions of these compounds. We use the formula: M 1 V 1 = M 2 V 2 M 1 and V1 represent the initial Molarity and volume and M 2 and V 2 represent the desired molarity and volume

### Dilution example:

Dilution example If we have 1 L of 3 M HCl , what is the molarity if we dilute acid to 6 L? M 1 = 3M V 1 = 1L M 2 = X V 2 = 6L M 1 V 1 = M 2 V 2 (3M) (1L) = (X) (6 L) X = .5 M 