Solubility: A Guided Inquiry Lab

Introduction:

The purpose of this lab is to identify a solid by making use of its solubility curve. Solubility is the maximum amount of solute that with be dissolved in a specific solvent. Any solution under the curve is considered unsaturated, as more solute can be added. Any solution on the curve (or above) is considered saturated, as more solute can not be dissolved. My lab partner, Alison, and I made our own procedure that involved heating the solution of the salt and water in a bath and then stirring the solution to see whether the salt dissolved or not.

Procedure:

1) First, we measured the 5g of the salt using a weigh boat and scale.

2) Next, we filled a quarter of a beaker with faucet water. We also measured 10mL of distilled water in a graduated cylinder and then transferred that into a smaller beaker.

3) We added the salt into the smaller beaker with the 10mL of distilled water. Then we put the larger beaker on the hot plate to heat it up, and placed the smaller beaker into the larger one. We held the smaller beaker in place with a pair of tongs to be make sure no extra water from the larger beaker entered.

4) We placed a thermometer into the solution with the salt, and waited until the temperature reached 44 degrees Celsius.

5) Once the solution reached 44 degrees, we removed the solution to stir it. 

6) Since the solute dissolved, we repeated the process, this time adding 4g into the solution, so it had a total of 9g of salt and the same 10mL of water.

7) Since the solute dissolved again, we knew which salt it had to be, and cleaned up.

Data:

Trial one:

Mass of solute = 5g

Mass of solvent = 10g

Temperature of solution = 44 degrees Celsius

Trial two:

Mass of solute = 9g

Mass of solvent = 10g

Temperature of solution = 44 degrees Celsius

Solubility (from graph):

NaCl at 44 degrees Celsius = 3.7g
KNO3 at 44 degrees Celsius = 7g
NaNO3 at 44 degrees Celsius = 10.7g

After stirring the solution in the first trial, the solute dissolved completely. After stirring the solution in the second trial, the solute again dissolved completely.

Discussion/Conclusion:

The solute we had was sodium nitrate (NaNO3). Our claim can be justified when taking the solubility graph into consideration. If the salt was sodium chloride (NaCl), 5g of it in 44 degrees Celsius would cause the solution to be saturated, meaning not all the solute would have dissolved. If the salt was potassium nitrate (KNO3), 9g of it in 44 degrees Celsius would cause the solution to be saturated. However, after 9g of the salt were added, all the solute still dissolved. The only other salt it could have been was sodium nitrate, because its solubility curve was above those of the other two. 

As the temperature of a solution (with a solid as the solute) increases, the solubility of the solid also increases.