Wanted: A Way To
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?
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.)
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:
- test tube
- Bunsen burner
- CBL with
- Temp. Probe
- Stirring rod
- 10 mL water
- 400 mL beaker
- utility clamps
- 100 mL grad. cylinder
- ring stand
- test tube rack
Info you need to know:
- 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.
- 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?
- 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?
- All you need is the CBL unit, no
- Plug in the temperature probe into
- Turn on CBL and hit the MODE button. It
should be recording the temperature in degrees C.
- Hold probe end in hand to test if temp.
- Set-up the wire on the ring stand as
demonstrated by teacher.
- Break down CBL set up when done. Be sure
to rinse, dry, and then wrap up probe wire.
- Set up Bunsen burner.
- Set up ring stand with screen, two hoops
- Make sure clamps are on tight.
- Have Mr. Jones check your set-up.
5. When done, be sure ring stand
set-up is put to the side.
- Get out following materials: test tube,
400mL beaker, test tube rack, glass stirring rod, graduated cylinder.
- Make sure test tube is dry and clean!!.
- Measure the # of grams of KCl your group
is testing from Mr. G.
- Add 20 mL of water to the KCl solute in
the test tube. Be precise in your measurement here!!!!
- Set up the test tube so it is clamped
onto ring stand and is in 400 mL beaker, but not touching bottom.
- Dump test tube contents down drain,
rinse test tube and return test tube to front of room, placing it upside down
in front rack.
- Prepare ice bath in 600 mL beaker, if
your group needs one
- 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.
- 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
****SAFETY RULES PARTICULAR TO THIS
- Make sure that the beaker does not touch the
- The TEACHER will move the test tube when it is
- 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
Grams of KCl
solute there are in
10mL of water
Grams of KCl solute there
would be in
100mL of water
Temperature when crystals
Temperature when crystals