Wanted: A Way To Determine Solubility

Solubility: is how well a solute dissolves into a solvent. It is almost easier to think of it as "dissolvability" of a substance. Note that solubility is a property of a substance, just as color and density are properties.

Can solubility be measured? Yes.

How?: The unit of measurement used for solubility is in grams/100mL of water at a certain temperature. (That's a complex unit of measurement!!)

Why?: You can only dissolve so much of a substance into water at a certain temperature. The graph; a solubility curve, helps you determine how many grams of a substance you can dissolve at a certain temperature (into 100 mL of water.)

Your job: You are to write a lab procedure so that you can make a graph for how well Potassium chloride (KCl) dissolves at various temperatures.

What you get:

Info you need to know:

  1. It is easy to tell when KCl has come out of solution. When it does, you can see crystals form right away. This can be seen under good lighting.
  2. Do you think those crystals will form when you heat the solution, or when you cool the solution? Which water molecules have more space between them: Cold or hot?
  3. The values for solubility are given in grams/100mL of water. Yet, you only have so much time to do your test. Therefore you need to do your test using only 10 mL of water in a test tube. How can you conduct a test for solubility using less than 100 mL of water? What would you then mathematically do with the results?

CBL Executives:

  1. All you need is the CBL unit, no calculator.
  2. Plug in the temperature probe into channel one.
  3. Turn on CBL and hit the MODE button. It should be recording the temperature in degrees C.
  4. Hold probe end in hand to test if temp. goes up.
  5. Set-up the wire on the ring stand as demonstrated by teacher.
  6. Break down CBL set up when done. Be sure to rinse, dry, and then wrap up probe wire.

BUNSEN Masters:

  1. Set up Bunsen burner.
  2. Set up ring stand with screen, two hoops and clamps.
  3. Make sure clamps are on tight.
  4. Have Mr. Jones check your set-up.

5. When done, be sure ring stand set-up is put to the side.

EQUIPMENT Handlers:

  1. Get out following materials: test tube, 400mL beaker, test tube rack, glass stirring rod, graduated cylinder.
  2. Make sure test tube is dry and clean!!.
  3. Measure the # of grams of KCl your group is testing from Mr. G.
  4. Add 20 mL of water to the KCl solute in the test tube. Be precise in your measurement here!!!!
  5. Set up the test tube so it is clamped onto ring stand and is in 400 mL beaker, but not touching bottom.
  6. Dump test tube contents down drain, rinse test tube and return test tube to front of room, placing it upside down in front rack.

RECORDERS:

  1. Prepare ice bath in 600 mL beaker, if your group needs one
  2. Record grams of KCl you are testing, the temp at which it begins to come out of solution, and observation/sketches of what you all observe in the lab: Colors, etc.
  3. With your group, discuss if there was any place where error could have occurred and how this could have been avoided. Record this info. Make sure your data/findings get posted on the computer spreadsheet.

****SAFETY RULES PARTICULAR TO THIS LAB****

  1. Make sure that the beaker does not touch the metal rings.
  2. The TEACHER will move the test tube when it is hot.
  3. Constant stirring of the solution does not mean over-stirring. Keep it gentle enough to not disturb the crystal formation process, but continuous enough to ensure that the heat is evenly distributed.

TRIAL

Grams of KCl

solute there are in

10mL of water

Grams of KCl solute there would be in

100mL of water

Temperature when crystals dissolved.

( C)

Temperature when crystals formed

( C)

1

3.4

     

2

4.0

     

3

4.5

4

4.8