Chapter 13: Supersaturation



Supersaturation of a Sodium Sulfate Aqueous Solution

Introduction and Purpose: The solubility of a solute is defined as the maximum amount of solute that will dissolve in a solvent. The solubility of most substances increases with increasing temperature. At any given temperature, when the maximum amount of solute is dissolved in the solvent, the solution is saturated.

It is possible, under certain conditions, for a solution to contain more solute than is normally found in a saturated solution. This type of solution is called “supersaturated” and is unstable. The addition of a single crystal, called a seed crystal, can often cause the entire solution to crystallize.

Materials and Methods: Normal lab apparatus and 2.80 g of sodium sulfate.

1) Place 2.80 g of sodium sulfate in a clean test tube. Add 12.8 ml of deionized water.

2) Using a test tube clamp, heat GENTLY over a hot water bath while stirring the tube gently until the entire solid dissolves. CAUTION: Point the test tube away from people!! Make sure the bottom of the test tube does not touch the bottom of the beaker. Warm the bottom and the sides of the tube evenly. NEVER heat only the tip of the test tube.

3) Place the test tube in a test tube rack. Add 0.03 grams of additional sodium sulfate to the test tube. Record your observations in the right hand column of your lab notebook.

4) Now place the tube in snow or ice water to cool. Be careful not to disturb the tube or its contents during the cooling process. If crystals begin to form in the solution, reheat the tube to re-dissolve the crystals and cool the tube again.

5) When the solution is cold, gently remove the tube from the ice water or snow. Place it in the test tube rack and add 0.03 grams of additional sodium sulfate into it. Gently flick the bottom of the tube with your finger. Record observations in the right hand column of your lab notebook.

6) Dispose of the crystals by washing them down the sink, using lots of water. Rinse your test tube three times with tap water and then three times with deionized water.

Results and Discussion: (To be answered after the lab in your chemistry notebook)

1. For steps 3, 4, and 5, tell whether the solution is unsaturated, saturated, or supersaturated. EXPLAIN HOW YOU CAN TELL.

2. Describe one simple test that will determine whether a solution is unsaturated, saturated, or supersaturated. EXPLAIN how you would interpret the test.

3. Define the following terms: Solution, solute, solvent, concentration, molarity, saturated, unsaturated, supersaturated.

Supersaturation of a Sodium Sulfate Aqueous Solution

Introduction and Purpose: The solubility of a solute is defined as the maximum amount of solute that will dissolve in a solvent. The solubility of most substances increases with increasing temperature. At any given temperature, when the maximum amount of solute is dissolved in the solvent, the solution is saturated.

It is possible, under certain conditions, for a solution to contain more solute than is normally found in a saturated solution. This type of solution is called “supersaturated” and is unstable. The addition of a single crystal, called a seed crystal, can often cause the entire solution to crystallize.

Materials and Methods: Normal lab apparatus, and 2.80 g of sodium sulfate.

1) Place 2.80 g of sodium sulfate in a clean test tube. Add 12.8 ml of deionized water.

2) Using a test tube clamp, heat GENTLY over a hot water bath while stirring the tube gently until all of the solid dissolves. CAUTION: Point the test tube away from people!! Make sure the bottom of the test tube does not touch the bottom of the beaker. Warm the bottom and the sides of the tube evenly. NEVER heat only the tip of the test tube.

3) Place the test tube in a test tube rack. Add 0.03 grams of additional sodium sulfate to the tube. Record your observations in the right hand column of your lab notebook.

4) Now place the tube in snow or ice water to cool. Be careful not to disturb the tube or its contents during the cooling process. If crystals begin to form in the solution, reheat the tube to re-dissolve the crystals and cool the tube again.

5) When the solution is cold, gently remove the tube from the ice water or snow. Place it in the test tube rack and add 0.03 grams of additional sodium sulfate into it. Gently flick the bottom of the tube with your finger. Record observations in the right hand column of your lab notebook.

6) Dispose of the crystals by washing them down the sink, using lots of water. Rinse your test tube three times with tap water and then three times with deionzied water.

Results and Discussion: (To be answered after the lab in your chemistry notebook)

4. For steps 3, 4, and 5, tell whether the solution is unsaturated, saturated, or supersaturated. EXPLAIN HOW YOU CAN TELL.

5. Describe one simple test that will determine whether a solution is unsaturated, saturated, or supersaturated. EXPLAIN how you would interpret the test.

6. Define the following terms: Solution, solute, solvent, concentration, molarity, saturated, unsaturated, supersaturated.

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