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:
- test tube
- Bunsen burner
- CBL with
- Temp. Probe
- KCl
- 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?
CBL Executives:
- All you need is the CBL unit, no
calculator.
- Plug in the temperature probe into
channel one.
- 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.
goes up.
- 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.
BUNSEN Masters:
- Set up Bunsen burner.
- Set up ring stand with screen, two hoops
and clamps.
- 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.
EQUIPMENT Handlers:
- 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.
RECORDERS:
- 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
computer spreadsheet.
****SAFETY RULES PARTICULAR TO THIS
LAB****
- Make sure that the beaker does not touch the
metal rings.
- The TEACHER will move the test tube when it is
hot.
- 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
|
|
|
|