Lab #3 Solubility and Equilibrium Lab
Background: Ionic compounds dissolve in solution to varying degrees. When ionic compounds dissolve, the ions
dissociate and move freely in solution surrounded by water molecules. When the solution is saturated, the maximum
amount has dissolved in that volume of water at that temperature.
Purpose:
To calculate and compare concentrations of different volumes of the same solution.
To visualize and explore the concept of equilibrium in solution.
To compare the degrees of solubility of different ionic compounds and calculate Ksp.
Pre-Lab Questions:
1. As more solute is added to the solvent, what happens to the concentration? Explain.
2. When is the solution saturated? If you add more solute will it dissolve? Explain.
3. Once the solution is saturated what do you suppose will happen to its concentration if you add more solute?
Explain your reasoning.
4. Describe how you would prepare a saturated solution.
5. The goal of the lab procedures is to determine the concentration of the saturated solution. In order to determine
the concentration of the solution, what will you need to measure? What equation will you use to calculate the
concentration?
5. How can you separate the solute from the solution?
Procedures:
A. Prepare a saturated aqueous solution of sodium chloride with dissolved sodium chloride and undissolved
solid.
Add salt while stirring until no more dissolves and some has settled to the bottom.
This will require a considerable amount of prolonged agitation.
Describe your observations of the dissolving process and saturated solution.
B. Separate the saturated solution from the undissolved solid.
Decant your saturated solution of sodium chloride to separate the saturated solution from the undissolved solid at
the bottom.
Describe the decanting process and how it separates the solution from the undissolved solid.
C. Separate the dissolved sodium chloride from 10.0 mL of saturated solution
Measure 10.0 mL of the saturated solution.
Measure and record the mass of the empty evaporating dish and watch glass cover.
HP- Measure the mass of the dish, cover and solution.
Heat the 10.0 mL of solution in an evaporating dish until it is completely dry. Once you observe no more steam
and the solid appears completely dry, continue to heat it for
another 30 seconds.
Describe your observations of the process of separation of solute and solvent
D. Determine the mass of NaCl in 10.0 mL of saturated sodium chloride solution.
Measure and record the mass of the evaporating dish with the sodium chloride.
Calculate the mass of sodium chloride in 10.0 mL of saturated solution.
E. Repeat the procedures with a saturated solution magnesium sulfate and calcium sulfate(25 mL).
Calculations:
1. Calculate the number of moles of NaCl isolated from the saturated solution.
2. Calculate the molarity of the saturated sodium chloride solution.
3. Write the equilibrium equation for the dissolution of sodium chloride.
4. Based upon your molarity calculation, what is the concentration of sodium ions?
What is concentration of chlorine ions?
5. Calculate the Ksp.
6. Repeat 1-5 for magnesium sulfate and calcium sulfate.
Analysis of the Reaction and Equilibrium:
7. WATER. Describe the water. Describe the polar covalent bond and the electrons in that bond that holds together
the water molecule. Explain the polarity of the water molecule. Describe the dipole-dipole attraction (hydrogen
bonds) between water molecules.
8. SODIUM CHLORIDE. Describe the formation of the ions. How does a sodium atom become an ion? How
does a chlorine atom become a chlorine ion? Describe the solid sodium chloride and the ionic bond between the
ions that holds together the solid salt.
9. DISSOLVING. Describe the dissolving of sodium chloride in water initially- before it reaches saturation. What
happens to the ionic bond? Where are the ions? What new attractions form? How are water molecules
involved? Include collisions. Write an equation for dissolving.
10. REACHING EQUILIBRIUM. Initially, the dissolving (forward) reaction is faster. As more sodium chloride
dissolves, what happens to the number of ions in solution? How does this affect the rate of crystallization (the
ions coming together to form the solid)? Draw a graph to show the change in rates over time.
11. SATURATED SOLUTION AND EQUILIBRIUM. Describe the equilibrium state of the saturated solution
you initially prepared. Include rates and conditions. What happens to the concentration of sodium chloride
dissolved in solution, once it is saturated? Are ions still moving into and out of solution? Write the equation to
show equilibrium.
12. DISSOLVING AND ENERGY. When one mole of sodium chloride is dissolved in a large volume of water,
3.88 kJ of energy are absorbed. Will the temperature of the surroundings and the solution increase or decrease?
Explain why. Is this reaction endothermic or exothermic? Describe the reaction in terms of energy and bonds.
Draw and explain a labeled energy graph. Is the reaction is favored or not based upon enthalpy?
13. COMPARING SOLUBILITY. Compare the molarity of the saturated solution of calcium sulfate and
magnesium sulfate. Which compound is more soluble? Explain what this means. How does the Ksp indicate
this? What does their solubility suggest about the strength of the ionic bond between these ions?
14. ELECTRICAL FORCE AND THE IONIC BOND.
a. The magnitude of electrical force acting between two charges depends directly upon the ___ and inversely
upon the ____. Copy and complete the sentence.
b. Use electrical force to predict which ion will be more attracted to an anion with a charge of -1: a +1 cation or
a +2 cation. Explain your reasoning.
c. Larger ions cannot get as close to each other as smaller ions. Use electrical force to predict which ion will be more
attracted to an anion with a charge of -1: a smaller +1 cation or a larger +1 cation. Explain your reasoning.
15. SILVER CHLORIDE AND SILVER NITRATE.
The concentration of a saturated solution of silver chloride is 1.34 x 10-5 M.
a. What does this indicate about the solubility of silver chloride. Explain. Compare the solubility of sodium
chloride and silver chloride. Compare the saturated solutions.
b. What does this suggest about the attraction between silver and chloride ions compared to their attractions to
water molecules? Explain.
c. Silver nitrate is fairly soluble. How would the Ksp of silver nitrate compare to the Ksp of silver chloride.
Compare the number of ions in a saturated solution of silver nitrate to the ions in solution of silver chloride.
Which has more ions in solution?
d. If silver nitrate solution is added to a solution of sodium chloride, what do you expect to happen? What will
happen to the ions in solution? Write an equation for this reaction.
e. Describe the reaction and formation of the precipitate. Compare the appearance of a solution with a soluble
compound to the appearance with an insoluble precipitate.
f. Write an equation for the reaction of silver nitrate and sodium chloride. Use a collision to explain the
formation of the precipitate.
HP- Complete these calculations for sodium chloride, magnesium sulfate and calcium sulfate.
1. Calculate the percent by mass.
2. Calculate the percent by mass.
3. Calculate the mole fraction.