INTRODUCTORY CHEMISTRY
NAME
LAB #20: SOLUBILITIES, PAGE 1
DECEMBER 7, 2006
Solubility of a Salt Compound
Constructing Solubility Curves to Study Saturation
INTRODUCTION/PRE-LAB DISCUSSION:
The solubility of a solute in a solvent is dependent on the quantity (in grams) of that solute that
will dissolve in the given quantity (mL) of solvent. Solubility varies with the temperature of the
solvent. For most solids, especially “salts”, in water (aqueous solutions) solubility varies directly
with the temperature. The higher the temperature of the solvent (water), the more solute (salt)
will dissolve in it. Take a look at the following series of three solubility curves, and review your
understanding of solubility by answering the questions that follow:
Pre-Lab Questions:
1)
What is the solubility (saturation) of potassium bromide at 20oC?
2)
What is the solubility of sodium chlorate (NaClO3) at 40oC?
3)
If 20 grams of sodium chloride are added to 100mL of water at 60oC, is the solution
saturated? What is the solubility at this temperature for sodium chloride?
INTRODUCTORY CHEMISTRY
LAB #20: SOLUBILITIES, PAGE 2
DECEMBER 7, 2006
NAME
Some important safety reminders:
1)
You will be using potassium nitrate today in lab. Though it is a fairly innocuous
substance, exposure to skin may cause itching and redness. So, wash hands after
exposure.
2)
Observe STANDARD PRECAUTIONS for this lab activity. You will be using hot
plates and hot water, so be careful not to burn yourself or any paper products and
wiring close to the hot plates.
APPARATUS/MATERIALS:
wire gauze
digital balance
ice water
250mL beaker
stirring rod
burner/heating apparatus
thermometer
test tube holder
1 large test tube
potassium nitrate OR ammonium chloride
600mL beaker
100mL graduated cylinder
PROCEDURE:
1)
Set up a hot water bath with a LARGE (600mL) beaker half-filled with HOT water. You
will NOT need the ring stand.
2)
Add 7.0 grams of ammonium chloride OR potassium nitrate salt (NOT BOTH) to a
massing cup. (NOTE: Select the salt that there appears to be the MOST of)
3)
Pour the 7.0 grams into a large test tube and then add 12mL of warm tap water.
4)
Heat the test tube in the hot water bath and stir until ALL of the salt has dissolved. If the
hot water starts to boil, add a little cold water to slow the boiling.
5)
Fill a 250mL beaker halfway with ice water (a little ice, but MOSTLY water).
6)
When ALL of the salt has dissolved, use the beaker tongs to remove the entire beaker and
test tube together from the hot plate. Place them on the wire gauze on the lab bench. Unplug
your hot plate!
7)
Place the thermometer INSIDE the test tube with the test tube still inside the hot water.
8)
Every minute or so, pour a little bit of ice water into your HOT beaker, NOT your test
tube. Estimate about 5mL at a time. After adding the cold water, use the test tube holder to
swirl the test tube in the beaker. The cold water should eventually cause the potassium nitrate to
recrystalize and come OUT of solution as a precipitate. Look for reappearance of the white salt.
If a white cloud starts to appear OR a white solid begins to crystallize out of the solution,
QUICKLY record the temperature of the thermometer.
9)
Calculate the solubility of the salt at this temperature by divide the mass by 12.0mL
10)
Rinse your test tube at the sink and flush the waste down the drain.
11)
Repeat steps #2-10 for the other masses of salt listed in the table in the Data/Observations
section.
INTRODUCTORY CHEMISTRY
LAB #20: SOLUBILITIES, PAGE 3
DECEMBER 7, 2006
NAME
DATA/OBSERVATIONS:
Grams of Salt
Grams of Salt / 12.0mL H2O
(Solubility)
Crystallization Temp. (oC)
4.0
5.0
6.0
7.0
ANALYSIS:
Use your Data Table to create graph of solubility using Microsoft Excel.