Lab 13B: Solubilty, A Guided Inquiry Lab

Lab 13B: Solubility, A Guided Inquiry Lab

Introduction: The purpose of this laboratory experiment was to test our knowledge of the process of solubility. We had to create our own procedure for determining the identity of the unknown solute that was to be dissolved in water. To do this we dissolved various amounts of the solute, the substance that was being dissolved, into the solvent, the substance that is dissolving the solute, in this case water. At different temperatures the solubility, or the amount a solute will dissolve in a solvent, changes. The higher the temperature, the higher the solubility and vice-versa. The purpose of the lab was basically to change the temperature and amount of solute to determine the identity of the solute. Other vocabulary terms were saturated- which is when a solution has dissolved the maximum amount of solute it can. Unsaturated- when a solution can still dissolve more solute.

Procedure: For this experiment we filled a beaker of water to 10 ml, and used a larger beaker to heat it up by putting the smaller beaker inside it. This removed temperature fluctuations. Then we dissolved approximately 4.30 grams of the substance at 36 degrees Celsius. It dissolved completely*, so we could rule of the NaCl substance because if it was NaCl it would have formed precipitate according to the solubility graph. The next part of the experiment was to increase the mass of solute to about 7.50 grams and keep the temperature at 40 degrees Celsius. When the water did not dissolve, we could confirm that the substance was not NaNO3, because it was under the solubility line and would have completely dissolved had it been NaNO3. To complete the final part of the experiment and confirm the identity of the substance, which at this point you can guess is KNO3, we increased the temperature to around 80 degrees Celsius and kept the mass at around 7.50 g. When we stirred the solution we noticed that the solid dissolved and this confirmed it at KNO3 because it was below the solubility line of KNO3. Some of the important materials we used were a graduated cylinder, a stirring rod, a scoopula, two beakers, a heating plate, a thermometer, a scale, a measuring plate, 10 ml water, and KNO3.

Data:

Mass of beaker- 29.74 g

Volume of water- 10 mL

Water temp- 21 C

Solute- KNO3

Conclusion: The unknown substance was KNO3. The reason we can be sure of the results was the evidence from the Solubility Chart. The first piece of evidence was that the solid did not dissolve at when we put conditions at 7 grams at 40 degrees. This did not dissolve and was under the solubility line for NaNO3 so we could rule out that substance. The next evidence was 4 grams of substance at 36 Celsius, and when it dissolved and was over the solubility line for NaCl we could rule it out as well. Therefore, the only substance it could possibly be was KNO3.

The illusive KNO3