MATERIALS & EQUIPMENT
APRON / GOGGLES / solute "A" (NaCl)large test tube / 250 mL beaker / solute "B" (KNO3)
Celsius thermometer / burner / ring stand
2 ring stand test tube clamps / ring / paper towel
10 mL graduated cylinder / beaker safety ring / cm ruler
heat diffusion screen / data sheet / scoopula (optional)
cold water
Procedure
CAUTION!!Lab chemicals are usually poisonous! If you get any of them on your skin rinse it off under the closest faucet. IF YOU GET CHEMICALS IN YOUR EYES rinse your eyes with the eyewash faucet for at least 15 minutes.
CAUTION!!Hot or boiling water may cause serious injury to your skin or eyes. KEEP YOUR APRON AND GOGGLES ON! WEAR THEM PROPERLY!
CAUTION!!Burners must be used according to the instructions given to you earlier by your teacher.
PROCEDURE -Phase 1
1. Put your goggles and apron on. WEAR THEM PROPERLY!
2. Loosen the large test tube clamps slightly and remove the test tube from the clamp by pulling it STRAIGHT UP and out of the top of the clamps.
3. Add water and then dump the contents in the SINK. Do this several times to get the tube clean. You may have to use a SCOOPULA to dislodge the used solute from the bottom.
4. Using a tightly twisted piece of paper towel, dry the inside of the test tube thoroughly and place it back in the clamps by pushing it straight down from the top.
5. Obtain a massing cup containing 10g of one of the solutes from the supply table. RECORD THE TYPE OF SOLUTE ON YOUR DATA SHEET.
6. Obtain EXACTLY 10 mL of water (from a faucet) in a graduated cylinder. You may have to use a pipette to get it exact.
DO NOT PUT THE WATER IN THE TEST TUBE YET!
7. Clean the bottom half of your thermometer with a piece of clean, wet paper towel.
8. Determine the temperature of the water in the graduated cylinder and RECORD IT ON YOUR DATA SHEET. LABEL IT.
9. Pour the solute from the massing cup into the test tube.
PROCEDURE -Phase 1(continued)
ATTENTION!! Immediately after the next step you should take the temperature of the mixture and begin stirring with the thermometer. You will have to take the temperature every 15 seconds for a total of 20 readings.
Note: Additional written observations may help you write conclusions and answer the discussion questions later .
10. Pour the water from the graduated cylinder into the test tube and immediately insert the thermometer into the mixture and RECORD THE TEMPERATURE .
11. MAKE A DRAWING OF THE BOTTOM QUARTER OF THE TEST TUBE. Try to show the level of the solvent and the level of the undissolved solute in correct proportion to each other. LABEL THE PARTS !
12. Measure the level of the undissolved solute and the solution with a cm ruler and record your measurements.
13. Start stirring the mixture and keep stirring constantly for five minutes. RECORD THE TEMPERATURE EVERY 15 SECONDS FOR THE NEXT 5 MINUTES.
ATTENTION!!
READ THE NEXT 7 STEPS CAREFULLY... BEFORE PROCEEDING WITH THE EXPERIMENT.
>READ THE CAUTION STATEMENTS ALSO.<
14. When you have 20 temperature recordings, stop stirring and MAKE A DRAWING OF THE BOTTOM QUARTER OF THE TEST TUBE. Try to show the level of the solvent and the level of the undissolved solute in correct proportion to each other. LABEL THE PARTS !
15. Again, measure the level of the undissolved solute and the solution with a cm ruler and record your measurements.
PROCEDURE -Phase 2
16. Obtain ABOUT 150 mL of hot water IN A 250 mL BEAKER .
17. Pull the test tube up in the clamp far enough to slide the beaker of water under the test tube.
18. Place the beaker on the heat diffusion screen and adjust the ring stand position so that the beaker is below the test tube and clamp.
19. Slide the test tube down into the hot water.
PROCEDURE -Phase 2 (continued)
CAUTION!!
YOU MUST FOLLOW PROPER BURNER PROCEDURE AS INSTRUCTED BY YOUR TEACHER.
- DO NOT ALLOW THE THERMOMETER BULB TO REST AGAINST THE BOTTOM OF THE TEST TUBE.
- IF THE TEMPERATURE GOES ABOVE 90oC REMOVE THE THERMOMETER!
20. Place the burner under the heat diffusion screen so that the flame is directly under the bottom of the beaker.
21. Place the thermometer back in the liquid if it has been removed and immediately RECORD the temperature.
22. Ask your teacher to light your burner.
23. Continue heating, stirring with the thermometer AND RECORDING THE TEMPERATURE EVERY 15 SECONDS. UNTILONE OF THE FOLLOWING EVENTS OCCURS:
- THE SOLUTE IS COMPLETELY DISSOLVED;
OR
- THE TEMPERATURE REACHES 90oC
then TURN THE BURNER OFF.
24. If the solute dissolves before the temperature reaches 90oC, turn off the burner quickly.
25. After the burner is out, remove the thermometer from the test tube, rinse it off and place it back in the case.
26. Make another drawing (3rd one) of the bottom quarter of the
test tube.LABEL THE PARTS!
27. Again, measure the level of the undissolved solute and the solution with a cm ruler and record your measurements.
PROCEDURE -Phase 3
Caution!! Do not touch the rings!
28. Loosen the test tube clamps and raise them high enough to allow the test tube to swing clear of the beaker. Leave the beaker in place on the ring stand.
CAUTION!!
DURING THE NEXT TEN MINUTES YOU SHOULD NOT JAR THE TEST TUBE. IF YOU NEED TO MOVE IT FOR BETTER OBSERVATION DO IT GENTLY!
PROCEDURE -Phase 3 (continued)
29. Looking through the side of the test tube and down from the top of the test tube....
- make a new drawing of the bottom 1/4 of the test tube every 3 minutes for the next 15 minutes.
NOTE: Fanning the tube with a piece of paper will speed up the cooling process.
- LABEL YOUR DRAWINGS WITH DESCRIPTIONS OF WHAT YOU SEE.
30. After six drawings have been made, gently pour only the liquid portion of the test tube contents in your sink. Watch what happens as it contacts the sink.
31. Examine the crystals that remain in the test tube. You may use a scoopula to dig them, but don’t handle them with your fingers.
32. Rinse out your test tube using the warm water in your beaker.
33. After you have completed the procedure for both kinds of solute (TWO DATA SHEETS),
complete the data summary/conclusion sheet for this experiment
NOTE: THE INFORMATION IN YOUR SCIENCE BOOK (ON SOLUTIONS) WILL HELP YOU GET A BETTER GRADE ON YOUR CONCLUSION QUESTIONS & THE EXTRA CREDIT.
Data Sheet
Temperatures readings while stirring solvent & solute without heat.
Temperature readings while stirring solvent & solute with heat.
(<STEP 29>)
Extra Credit
1. During the cooling phase, why did crystals form at the surface of the solution first?
2. Use the solubility chart at the right to answer this question.
If we had used a third substance ( “C” ) and found that it did not completely dissolve at 23oC, but it dissolved completely when heated to about 40oC, which of the substances on the chart could it be?
Keep in mind that the chart is for 100 mL of water and you only had 10 mL of water and 10 g of solute.
Explain your choice for #2 below.
3. Compare the precipitation that occurred in the test tubes to the precipitation that occurs in our atmosphere.
Conclusions
Date HourName Table No.
Write the definition forsolubility.
Examine the information and drawings on your data sheets and compare the two substances (differences and similarities).
1. How does the solubility of the two solutes compare when the solvent is at room temperature?
Be sure to explain how your data and observations support your comments.
2. How does the solubility of the two solutes compare when the solvent has been heated?
Be sure to explain how your data and observations support your comments.
3. Explain in detail how your results compare to your hypotheses for each question.
Be sure to explain how your data and observations support your comments.
CONTINUE ON THE OTHER SIDE IF NECESSARY.
IMPORTANT !! Staple your hypothesis sheet and both data sheets to this page before you hand it in.
1. During the heating phase of the NaCl portion of the lab, the temperature rose rapidly after the test tube was placed in the beaker. Later, many students noticed that the temperature was not increasing as rapidly. What could have caused this difference in rate of temperature increase?
2. What is meant by the term solubility?
3. How does a concentrated solution compare to a dilute solution?
4. What is a saturated solution?
5. What is a precipitate?
solubility & temperature lab.doc 10/20/2018