Lab 13: Solubility: A Guided Inquiry Lab

Introduction:
In this lab, we identified an unknown salt using the solubility curves of known solids (NaNO3, KNO3, and NaCl). Solubility can be defined as the ability for a substance to dissolve and solubility often increases as temperature increases (which creates the solubility curve). In a solution, there is always a solvent and solute. A solvent can be defined as a substance that dissolves another while a solute is defined as the minor component dissolved in a solution. My lab partners and I created a procedure involving the heating of water to dissolve certain amounts of the mystery substance. By finding the solubility of the substance, we were able to use the given solubility curves to identify the substance.

Procedure:

1. First, we measured out 10 mL of distilled water in a small graduated cylinder and poured it into a small beaker.
2. We began heating our hot water bath (the distilled water beaker in a larger beaker filled with regular water) to our chosen temperature of 45°C using a thermometer and a hot plate. We chose 45°C because that temperature had a large variation in solubility between the three solubility curves, therefore it would be more easy to distinguish between the different substances after finding the solubility of the mystery salt.
3. While the hot bath heated up, we measured out 4.8 g of the mystery salt using a scale. We wanted to use 4.8g of solute at first because it clearly lies over the NaCl curve, but under the KNO3 curve.
4. We poured the 4.8g of solute into the small beaker with distilled water and mixed the solution with a stirring rod. After a few minutes we found the solution remained unsaturated since all the solute dissolved in the solvent. This means the substance is not NaCl.
5. We continued to mass and add 3.5 g more of solute because a total of 8.3g of solute lies over the KNO3 curve while definitely lying under the NaNO3 curve. After a few minutes, all the added solute dissolved in the solution and the solution still remained unsaturated. This means the substance is also not KNO3.
6. By now, we knew the substance must've been NaNO3, but we continued our third test for confirmation. We massed and added 3.4g to our previous solution and later found our solution was finally saturated. This meant our substance was for sure NaNO3.

Data:
Trial 1 (NaCl testing)- Dissolved solute (unsaturated solution)
Mass of solute: 4.8g
Mass of solvent: 10g
Temp: 45°C

Trial 2 (KNO3 testing)- Dissolved solute (unsaturated solution)
Mass of solute: 8.3g
Mass of solvent: 10g
Temp: 45°C

Trial 3 (NaNO3 testing)- Undissolved solute (saturated solution)
Mass of solute: 11.7g
Mass of solvent: 10g
Temp: 45°C

Concluding Summary:
The mystery solute we had was NaNO3. Our claim was justified when we found that 4.8g of solute (above the NaCl solubility curve) and 8.3g of solute (above the KNO3 solubility curve) both fully dissolved and produced unsaturated solutions. Our third test for NaNO3 produced a saturated solution, meaning NaNO3 was certainly our substance. The relationship between the solubility and temperature is that as the temperature of a substance increases, the solubility of the substance also increases. This relationship in the solubility curves is what overall helped us identify the mystery salt.