Solubility: A Guided Inquiry Lab

Introduction:

During our solubility: a guided inquiry lab, we were tasked with creating and implementing a procedure to identify an unknown solid using experimental data and known solubility data. Solubility is the ability for a given substance, the solute, to dissolve in a solvent. The solvent is the liquid you are dissolving the substance into. We were able to use hot plates, balances, test tubes, a thermometer, beakers, erlenmeyer flasks, and stirring rods. The way we knew if we had the right substance was based on if our solution was saturated. A saturated solution is a solution in which no more solute can be dissolved in the solvent. The saturation of the solution has been achieved when any additional substance that is added results in a solid precipitate which collects at the bottom of the beaker. The solid we had to identify was in container "A".

Here is a picture of our known solubility data:

Procedure: 

My partner and I started by filling a small beaker with 10 mL of water and heating it up on a hot plate till it was 50℃. While the water was heating up, we measured out 5 grams of our unknown solid. We did 5 grams because when we looked at our solubility graph, we saw that 5 grams was above the NaCl line so if the solid did not dissolve we would know that our unknown solid was NaCl. As soon as the water was 50℃, we poured the 5 grams of our solid into the water and stirred it to see if it dissolved. It fully dissolved so we now knew that our solid was not NaCl.

We then put our beaker back onto the hot plate so we can keep the water at 50℃ while we measured out 2 more grams of our known solid. After the water was heated again, we poured the 2 grams of solid into our beaker and stirred it; Now we had a total 7 grams of our solid in the beaker. The solid fully dissolved again so it did not give us any new information about the identity of our solid, it just proved the fact that our solid was not NaCl.

We put the beaker back on the heat again and measured out 2 more grams of our solid. When the water was heated, we poured the 2 grams of solid that we had just measured out and started stirring it. Now we had a total of 9 grams of our substance. Looking at our solubility graph we saw that if these 2 more grams of solid dissolved, our substance would be NaNO₃, and that if it did not dissolve our substance would be KNO₃. We saw that the solid fully dissolved into the water which told us that the only possibility left for the identity of our unknown solid, was NaNO₃.

Here is a picture of our set up:

Here is a table of my data:

Conclusion:

In the end we found that our unknown solid in container "A" was NaNO3. We know that we are correct because when we dissolved 9 grams of the solid into our 10 mL of water, it fully dissolved and the solubility graph shows that if our substance was any of the other two options, the solution would have been saturated, which it wasn't. We also initially thought that our substance was KNO3 because our solute wasn't dissolving into the water but we realized that our water was only heated to 45℃ so we reheated the water to 50℃ and it dissolved completely which officially ruled out that our substance was KNO3. Also, for any solid substance, when temperature increases, solubility also increases which is how why every time we reheated the water, we kept adding more of our solid.