Potassium Nitrate Lab

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Purpose: Collect the experimental data necessary to construct a solubility curve for potassium nitrate (KNO3) in water.

Materials: Balance, hot plate, microspatula, 4 boiling tubes (18 x 150-mm), boiling tube holder, boiling tube rack, 400-mL beaker, thermometer, graduated cylinder, stirring rod, iron ring, utility clamp, wire gauze, marking pencil, potassium nitrate (KNO3), distilled water, safety goggles, lab apron


Procedure:
1. Using a marking pencil, the boiling tubes were labeled 1 through 4. They were placed on the boiling tube rack.
2. On a balance, exactly 2.0 g of potassium nitrate (KNO3) were measured out. The salt was poured into boiling tube #1.
3. Step 2 was repeated for the following masses of KNO3 and added to the boiling …show more content…

Exactly 5.0-mL of distilled water was added to each boiling tube.
5. A 400-mL beaker was filled about three-fourths full with tap water. This was used a water bath. The beaker was placed on a hot plate and heated to 90C and the temperature was adjusted to maintain the water at about this temperature.
6. The KNO3-water mixture was stirred with a glass stirring rod until the KNO3 was completely dissolved. The stirrer was removed and rinsed. Using the boiling tube holder, the tube was removed.
7. Step 6 was repeated with boiling tube #2 and a warm thermometer (after being placed in the hot water bath) was placed into the solution in boiling tube #1. The boiling tube was held up to the light and the first sign of crystallization was observed As the instant crystallization began, the temperature was observed and …show more content…

2.0g/5.0-mL x 20 = 40.g/100-mL
4.0g/5.0-mL x 20 = 80.g/100-mL
6.0g/5.0-mL x 20 = 120g/100-mL
8.0g/5.0-mL x 20 = 160g/100-mL
2. See graph paper for 2 and 3.

Conclusions and Questions:
1. A. 30C: 30g KNO3
B. 60C: 105g KNO3
C. 70C: 130g KNO3
2. Saturated is a term describing a mixture that already contains the maximum amount of solute that will dissolve at that temperature. When a solution can hold more solute than it currently contains, it is called unsaturated. When a solution contains even more that solute than will dissolve, it is supersaturated.
3. A. Supersaturated because that point falls about the solubility curve for KNO3.
B. Unsaturated because that point falls below the solubility curve for KNO3.
4. No, not all ionic compounds fit that description, however the solubility of most ionic compounds increase along with the temperature. When a substance dissolves, it goes from a solid to a liquid, which is an endothermic reaction. When heat is added and the temperature become higher, the extra heat favors the endothermic reaction causing more solid to dissolve rather than crystallize.
5. The solubility of a gas decreases with temperature (e.g., cold water will hold more gas than hot water). For sketch, see back of graph

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