Lesson 4: Wrap Up
In this lesson we have studied a variety of things relating to concentrations of solutions. There are several different ways of expressing concentration: weight percent, volume percent, weight/volume percent, molarity, and normality. We have worked with calculations that relate M to moles of solute and volume of solution and also formula weight as well as color intensity. We looked at how, in reversible reactions, the concentrations of the chemicals in equilibrium are related to one another by the solubility product constant, Ksp, for the equilibrium.
As you complete your work on this lesson, be sure to review the objectives and get lots of practice. Take the self quiz and check your answers. Answer the questions in the problem set to be turned in. Write up a lab report of your experimental work to be turned in.
Self Quiz
Select the letter of the best answer for each of the following questions.
1. What is the molarity of the solution which contains 5.0 g of NaOH (formula weight = 40 g/mole) dissolved in water to make 200 mL of solution?
a. 0.025 M
b. 0.13 M
c. 0.20 M
d. 0.63 M
e. 1.6 M
2. What is the weight percent of NaCl in a solution made by dissolving 20 g of NaCl (FW = 58 g/mole) in 200 mL of water?
a. 0.16%
b. 0.17%
c. 9.1%
d. 10%
e. 17%
3. When 40.0 mL of 2.0 M NaCl (FW = 58) is diluted to 100.0 mL, what is the new concentration?
a. 0.20 M
b. 0.50 M
c. 0.80 M
d. 5.0 M
e. need more information to answer this question
4. How many moles of NaOH (FW = 40 g/mole) are there in 50 mL of 0.30 M NaOH solution?
a. 0.006
b. 0.015
c. 0.60
d. 6
e. 15
5. What is the species concentration of Na+ in a 0.50 M solution of Na2SO4?
a. 0.20 M
b. 0.25 M
c. 0.50 M
d. 1.0 M
e. 2.0 M
6. How many moles of chloride ion are there in 100 mL of 0.50 M AlCl3?
a. 0.050
b. 0.10
c. 0.15
d. 0.5
e. 1.5
7. Which is the most appropriate concentration unit for use in colorimetry?
a. molarity
b. normality
c. volume percent
d. weight percent
8. If the absorbance of a 0.340 M solution of a chemical is 0.18 at a particular wavelength, what is the concentration of a solution of the the same chemical that has an absorbance of 0.023 measured at the same wavelength?
a. 0.012 M
b. 0.027 M
c. 0.043 M
d. 2.7 M
Answer the following questions.
9. What is the appropriate equilibrium constant expression for this reaction?
CaCl2(s) 
Ca2+(aq) + 2 Cl-(aq)
10. If the solubility of CaCl2 is 74.5 g in 100 mL, what are the species concentrations of Ca2+ and Cl- and what is the value of Ksp for CaCl2?
Self Quiz Answers
1. What is the molarity of the solution which contains 5.0 g of NaOH (formula weight = 40 g/mole) dissolved in water to make 200 mL of solution?
*d. 0.63 M
2. What is the weight percent of NaCl in a solution made by dissolving 20 g of NaCl (FW = 58 g/mole) in 200 mL of water?
*c. 9.1%
3. When 40.0 mL of 2.0 M NaCl (FW = 58) is diluted to 100.0 mL, what is the new concentration?
*c. 0.80 M
4. How many moles of NaOH (FW = 40 g/mole) are there in 50 mL of 0.30 M NaOH solution?
*b. 0.015
5. What is the species concentration of Na+ in a 0.50 M solution of Na2SO4?
*d. 1.0 M
6. How many moles of chloride ion are there in 100 mL of 0.50 M AlCl3?
*c. 0.15
7. Which is the most appropriate concentration unit for use in colorimetry?
*a. molarity
8. If the absorbance of a 0.340 M solution of a chemical is 0.18 at a particular wavelength, what is the concentration of a solution of the the same chemical that has an absorbance of 0.023 measured at the same wavelength?
*c. 0.043 M
Answer the following questions.
9. What is the appropriate equilibrium constant expression for this reaction?
CaCl2(s) Ca2+(aq) + 2 Cl-(aq)
Ksp = [Ca2+]x[Cl-]2
10. If the solubility of CaCl2 is 74.5 g in 100 mL, what are the species concentrations of Ca2+ and Cl- and what is the value of Ksp for CaCl2?
Concentration of CaCl2 = [ 74.5 g / (111.1 g/mole) ] / (0.100 L) = 6.71 M
[Ca2+] = 6.71 M [Cl-] = 13.4 M
Ksp = [Ca2+] x [Cl-]2
Ksp = ( 6.71 M ) ( 13.4 M )2
Ksp = 1.20 x 103