lab for chemistry

Question

Objectives

1. Prepare a supersaturated solution of salt.
2. Observe the effect of adding a small seed crystal to the supersaturated solution.

Supersaturated Lab Video Link

  

Double click on 

picture then click on 

the white play button

in the drawing tool.

 

 

 

 

 

 

Materials

1 test tube

Test tube holder

100 ml beaker

10-ml graduated cylinder

Sodium thiosulfate 

Na2S2O3 

Gas burner

Centigram Balance

Test tube rack

Distilled water

Ice

Rubber stopper

Procedure

1. Place 6.04g of Na2S2O3· 10H2O in a clean dry test tube. Add 2 ml distilled water.
2. Place a stopper on the test tube and agitate the contents of the test tube for 30 seconds.
3. Describe which type of solution was formed in your observations. 
4. Holding the test tube with the test tube holder, heat it in a burner flame, agitating the mixture gently until the entire solid has dissolved. CAUTION: When heating a test tube, never point the mouth of the tube at yourself or anyone else. Record your observations.
5. Place the test tube in a test tube rack. 
6. Add one more crystal of the solid Na2S2O3 to the warmed solution and gently agitate.
7. Record your observations.
8. Place the test tube and its contents in a beaker of ice to cool. Be careful not to disturb the test tube during the cooling process. If the crystals begin to form as the tube is cooling, reheat the tube to redissolve the crystals and cool the tube again.
9. When the solution is cool, gently remove the tube from the ice water bath and put it in the test tube rack. Add one small crystal of Na2S2O3. Record your observations.

Procedure Step	Observations
3	What type of solution was formed?
4
7
9

Analysis

1. Why is it necessary to heat the mixture in Step 4?

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1. What type of solution may contain more solute than is normally contained in a saturated solution at the same temperature?
2. unsaturated
3. saturated
4. supersaturated

1. Which of the following steps formed saturated solutions?
2. step 3 and step 4
3. step 4 and step 7
4. step 7 and step 9
5. step 3 and step 9

1. At the end of Step 9, when the crystallization is complete, is the solution unsaturated, saturated or supersaturated? Support your answer to receive full credit. 

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Answer 1

Hello, Jett,

The video rovides the data that are to be entered in the handout, including the steps taken (e.g., "grams of salt dissolved in water and heated to X." It would help if you completed that process and then ask whatever question you had. I don't see any question, other than what are asked during the video. Please answer what you can, and then post your question.

I did note that crystallization occured after dropping a crystalling salt into the supersaturated solution. Precipitation is due to the presence of a "nucleation site," a surface having properties that allow other dissolved molecules to drop out of solution and organize in an energy-reduced state on the surface of the crystal.

Thanks,

Bob