8th Grade Lab Science (Cribb & Duane)
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Background:  Many solutions are colorless there is nothing to be seen once the solid is dissolved, while other chemicals have some color.  This adds a challenge in determining whether or not a colored substance is soluble or insoluble.  You will conduct a quantitative study of a solution that has color.  A solution in which no more solid can be dissolved is called a saturated solution.  Once you have prepared a saturated solution, you will measure the solubility of the colored substance.

 

Part I Dissolving

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Place 5.0 mL of water in one test tube, and 20.0 mL of water in another test

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Add 0.60 g of copper sulfate (CuSO4), the blue chemical, to each test tube

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Plug with a rubber stopper and shake thoroughly.

 

Part I Questions:

1.      Did all of the solid dissolve in both test tubes?

2.      What is the solvent of this solution?  The solute?

3.      Is the color uniform within both test tubes?

4.      Do you think that each cubic centimeter (mL) of solution contains the same mass of dissolved material?

5.      Both test tubes contain the same mass of dissolved substance, but is the shade of color the same in both test tubes?

 

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Part II Preparing a Saturated Solution

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To each test tube, add an additional 0.60 g of copper sulfate (CuSO4) so that there is a total of 1.20 g of copper sulfate.

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Plug with a rubber stopper and shake thoroughly.

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Continue to add 0.60 g of copper sulfate into the test tubes until you can observe solid particles (precipitate) on the bottom.

Part II Questions:

1.      Did 1.20 g of solid dissolve as well in 20.0 mL as 5.0 mL?  Did 1.80 g dissolve as well?

2.      Is the color uniform in each solution?

3.      How do you determine when a solution is saturated?  Which test tube became saturated first?  Why do you think this is so?

4.      Predict how much solid do you think there would have to be in the 20.0 mL test tube so that not all of it would dissolve.  Test your prediction

 

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Part III Measuring Solubility

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In your test tube that is saturated, decant the liquid by pouring only the liquid portion into a graduated cylinder.

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Measure and record the volume in mL (be precise).

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Measure and record the mass of an empty evaporation dish (crucible)

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Carefully pour the solution into the evaporation dish and gently heat the dish with a burner until all of the liquid is boiled way.

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Measure the mass of the dish and the solid left behind and subtract to determine the mass of the solid that dissolved.

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Apply the formula below

solubility = (mass solute / volume of solvent) x 100

Part III Questions:

1. What units measure solubility?

2. Did any of the copper sulfate boil away along with the water?  Why or why not?

3. What is solubility?

4. According to your data, what is the solubility of copper sulfate?

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Solubility Lab Handouts:

solubility of copper sulfate

data table (blank) solubility of copper sulfate

data collected Nov 5th