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Name ___________________________________Chem 162, Section: _____Group Number: ______

ALE 25. Units of Concentration

(Reference: 13.5 Silberberg 5th edition)

How do you convert from one unit of concentration to another?

Your Goal: to be able to convert from one unit of concentration in the model below to any other unit

of concentration in the model using dimensional analysis (factor-label method) to show

your work.

1. The first step in achieving this goal is to memorize each unit of concentration in the model below...

The Model: Units of Concentration

2. Your task now is to practice applying using these units of concentration. Consider the following

questions when solving problems involving conversion of one unit of concentration to another:

a. What are the units of concentration given in c. What is (are) the conversion factor(s) needed to

the problem? get the desired unit of concentration?

b. What are the units you are converting to? d. Set up the problems using dimensional analysis.

Units should cancel to give the units desired.

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ALE 25 - Chem 162 - K. Marr (Last Revised Winter 2010)

3. Useful Conversion Factors

To convert between... Conversion factor Units of conversion factor

moles of a substance and its mass molar mass or molecular weight g / 1 mol

mass of a substance and its volume density, d g / 1 mL or g / 1 L (for gases)

moles of solute to volume of solution Molarity, M mol solute / 1 L solution

moles of solute to kg solvent molality, m mol solute / 1 kg solvent

Exercises

Use dimensional analysis (factor-label method) and correct significant figures to solve the following

problems. Circle you answer for each question.

1. Calculate the molarity of a solution made by diluting 25.0 mL of 6.15 M HCl to a volume of 0.500 L

with water. Circle your answer.

2. How would you prepare 3.5 L of 0.55 M NaCl from solid NaCl? Circle your answer.

3. Calculate molality of a solution containing 164 g of HCl in 753g of water. Circle your answer.

4. Calculate the molality of a solution consisting of 2.77 mL of carbon tetrachloride (CCl4, d = 1.59

g/mL) in 79.5 mL of methylene chloride (CH2Cl2, d = 1.33 g/mL) Circle your answer.

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ALE 25 - Chem 162 - K. Marr (Last Revised Winter 2010)

5. A 28.8 mass % aqueous solution of iron (III) chloride has a density of 1.280 g/mL.

a.) Calculate the molality of the solution. Circle your answer.

b.) Calculate the molarity of the solution. Circle your answer.

c.) Calculate the mole fraction of FeCl3. Circle your answer.

6.a. How many grams of solid NaOH are needed to prepare 250.0g of 1.00% (w/w) NaOH in water?

Circle your answer.

b.) How many grams of water are needed? Circle your answer.

c.) How many mL of water at 20.0 oC are needed? (dwater at 20.0 oC = 0.9882 g/mL) Circle your

answer.

d.) What is the molality of the solution? Circle your answer.

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What is the formula for molar concentration? Molarity (M) = Moles (n)/ Volume of the Solution (L) Here, the symbols are mentioned after each of the scientific terms used in the formula. Hence, the unit of molar concentration is expressed in moles/liter. It is easy to determine the molar concentration formula by studying the expressions explained elaborately.

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