1. Molarity Measurement of Concentration of the Solutions
(Session 18)
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2. Concentration of solutions
The concentration of a solution expresses the amount of solute present in a given amount of solution.
The words concentrate and dissolved solution are just expressions, in which neither of them gives us an indication of the exact amount of solute present.
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3. Methods to determine concentration
There are many methods to give us the concentration of solutions, some of them are:
Weight percentage
Volume percentage
Molarity
Molaliity
Normality
In this session we will study the concentration measurement called Molarity.
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4. Number of moles in a compound = grams
We represent molarity with the letter M in caps and its solutions are known as Moles.
Molarity is defined as number of solute moles in a liter of solution.
M = Moles of Solute
liter of solution
A solution 5 M of NaOH has 5 moles of NaOH in a liter of solution.
Number of moles in a compound = grams
Molecular Weight
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5. Ciencias de la Tierra II
Activity 1
Prepare a watery solution 1 M of Calcium Bromine.
1 mol of CaBr2 = 200 g of CaBr2
As a result 200 g of CaBr2 are dissolved in enough water until completing 1 L of solution.
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The Molar concentration is especially useful to make stoichiometric calculations in solutions…
Molarity is one of the concentration measurements used more in the industry, chemical labs and doctors.
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Activity 2
How many grams of NaCl do you need to prepare a 0.15M solution in 1 liter (MW 58.5)
Step One: Calculate Moles of solute
We know that Molarity = Moles of solute/ L
In the problem above we are given M and L
SO, lets solve it.
.15M=x moles of solute/ 1L
X= .15mol / L * 1L
X = .15mol
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Activity 2 continued
Since we have the moles, now we can calculate the grams
Use the formula
# of moles in a compound = grams/MW
.15mol=x grams/ g/mol NaCl
X = .15mol * 58.5 g/mol
X= 8.8g
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Activity Three
How many grams of glucose do you need to prepare a 1.5M solution in 5 liters (MW glucose is 180g/mol)
First calculate Moles of Solute
Then calculate grams
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10. Write these problems out and have your teacher check your answers
How many grams do you need for a 0.400M solution in 1 liter of Copper Sulfate (MW g)?
How many grams of Potassium nitrate and in a 0.800M solution in 2.5L (MW g)
What mass of sucrose must be dissolved to make 460ml of a 1.10M solution (MW 342.3g)
What mass of Lithium chloride must be dissolved to make a 0.194M solution that has a volume of 1L. (MW 42.4g)
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Activity 4
Now, lets calculate Molarity if we are given grams….
You add 32g of Potassium Chloride (MW 74.6) to a flask and add 955ml. What is the molarity?
First we must find out the moles (m=gr/MW)
Then we can calculate molarity (M=m solute/L)
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Activity 5
What is the molarity of a solution that contains 25.1g of KI in 4.3L of solution? (MW 166g)
What is the molarity of a solution that contains 10.6g of Potasssium Nitrate in a 705ml solution? (MW 101g)
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13. Ciencias de la Tierra II
Bibliography
Brown, T. et al. (1991) Chemistry: The Central Science. 5th ed. United States of America: Prentice Hall.
Burns, R. (1996) Chemistry Fundaments. 2nd. ed. United States of America: Prentice Hall.
Chang, R. (1992). Chemistry. 4th ed. United States of America: McGraw Hill.
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