Temperature and Solubility

Title: Effect of Temperature on Solubility of a Salt

Problem: How does temperature affect the crystallization of KNO3?

Introduction:

In the lab, the independent variable is the potassium nitrate. The salt (KNO3) is put in every test tube, and different amounts are put into each one. The solubility of salt in the water is being affected by the temperature. The higher the temperature the more energy there is in the water, this makes it easier for the potassium nitrate to break apart and dissolve into the water. The effects of the temperature on solubility is important because when making scientific solutions, it is important to know what you need to use when making them.

Hypothesis:
If the temperature rises, the KNO3 will dissolve faster because of more energy in the container provided by the heat.

Materials:

• Computer
• Vernier computer interface
• Logger Pro
• Temperature Probe
• 2 Utility Clamps
• Four 20 times 150 mm-test tubes
• Test tube rack
• Ring Stand
• Hot Plate
• Stirring rod
• Potassium Nitrate (KNO3)
• Distilled water
• 400 mL beaker
• 10 mL graduated cylinder or pipet
• 250 mL beaker

Procedure:

Get and wear goggles. Label each test tube 1-4. In the test tube labeled 1, put 2 ml KNO3. In the test tube labeled 2, put 4 ml KNO3. In the test tube labeled 3, put 6 ml KNO3. In the test tube labeled 4, put 8 ml of KNO3. Add 5 ml distilled water to each one. Open the Logger Pro software and connect the Vernier computer interface to the computer. In channel 1, attach the temperature probe. Fill a 400 mL beaker three-fourths full of tap water. Place it on a hot plate situated on (or next to) the base of a ring stand. Heat the water bath to about 90°C and adjust the heat to maintain the water at this temperature. Place the Temperature Probe in the water bath to monitor the temperature and to warm the probe. Use the utility clamp to fasten one of the test tubes to the ring stand. Lower the test tube into the water. To dissolve all of the KNO3, Test Tubes 3 and 4 need to be heated to 95º C than Test Tubes 1 and 2. Use the stirring rod to stir the mixture until the KNO3 is completely dissolved. Don’t leave the test tube in the water bath any longer than is necessary to dissolve the solid. When the KNO3 is dissolved click the collect button and put the temperature probe into the test tube. Bob the probe up and down in the tube while waiting for crystals to form. Once crystals start to form, click keep. Put the solubility value in the edit box and press the enter key. After the data pair has been saved, return the test tube to the test tube rack and place the Temperature Probe in the water bath for the next trial. Repeat the same steps with the other 3 test tubes. When the data is finished collecting, click stop . Record the temperature (in °C) from the four trials in the data table.

Data and Analysis:
The water in the third and second test tube cooled causing the solubility to rise. The hot water dissolved the salt because the molecules separated and there was room for the salt particles, but when it cooled, there was no longer any room since the molecules pul ed together, so the solubility had to rise since the molecules were forced to crystalize. The first and second solubility rose with higher temperatures because there was more room for the molecules to stay dissolved when they were cooled. At 110g of KNO3 in 100g water at 27.7ºC , it would be unsaturated. At 60g of KNO3 in 100g water at  35.8ºC, it would be saturated. At 140g of KNO3 in 200g water at 76ºC, it would be saturated. Yes because the small amount of solute has room to dissolve in the 50ºC of water since the molecules will be separated a pretty good deal.
No because that much of solute does not have room to dissolve with the other molecules still that close together because of the temperature. I would say about 15 g of solute because the molecules wouldn’t make enough room for anymore salt than 15 g. Also, because 40 g of solute was used in 90ºC water, so since it is about cutting the degree in half, the amount of solute would be to.

Test Tube Number	Amount of KNO3 used per 5 mL H20	Amount of KNO3 used per 100 g H20
1	2.0	40
2	4.0	80
3	6.0	120
4	8.0	160

Original Graph taken from Logger Pro:
Graph we had to make do to the error:
Lab setup:



Beaker setup:

Trial	Solubility (g / 100 g H₂0)	Temp (℃)
1	40.0	24.7
2	80.0	35.8
3	120.0	76
4	160.0	84

Conclusion:

In the end, my hypothesis was wrong. As it was colder, it was more soluble as shown in Graph 1. There are changes that could have been made like adding more KNO3 or adding more water. If you added more KNO3, I think it would take a colder temperature to dissolve it. If you added water, there would be no telling what could happen after seeing the data.  You could also use other element combinations to see other reactions. Those different changes could discover something completely new. We did have a couple of errors during our experiment. For instance, when we were graphing our data and we stopped recording, we hit the keep button which messed with the chart. It graphed the data in the wrong areas as shown in our first graph where the shape is rhombus. If we didn’t catch this our data would have been thrown off. Due to this mistake, we had to make our own chart with what we had as the right data and when you do this it is risky because you could put the wrong data in. Another error in our data is that when we were doing each test, we needed the starting temperature to be at 90 degrees but sometimes we could not get the temp to stay at exactly 90 which will also cause a difference in our data.