Conceptual Chem
Solubility Lab
1C3 – solubility curve lab
Name ________________________
Purpose: To gather laboratory data in order to construct a solubility curve.
Procedure:
1. Assemble the apparatus as shown. The bulb of the thermometer should be
placed about 2 cm from the bottom of the test tube.
2. Weigh 6 to 7 grams (the exact weight must be known – record it in your data
chart now!) of Potassium Nitrate and pour the salt into the dry test tube (Note
– you only add salt to the tube one time in this experiment).
3. Add 4.0 mL of water to the test tube. Heat the test tube in the water bath until
the salt dissolves. You should stir the solution to help it dissolve, but no
amount of stirring will help until you get the tube to at least 60 Co for the first
trial.
4. Once the salt has dissolved, remove the test tube and clamp from the ring
stand. Place the test tube in a beaker of tap water (a cold water bath) and stir
constantly. Record the temperature when the crystals first appear. If you miss
finding the right temperature, you can always put the tube back in the hot
water, get it to dissolve, and then try again.
5. Add water to the test tube (2.0 mL) and then repeat the experiment (that is, stir
and reheat until the salt dissolves, then put in the cold water bath – don’t add
more salt, just more water). Then add water in the following amounts and
repeat the experiment: 2 mL, 4 mL, 4 mL, and 4 mL. For the last few
observations, you may have to add ice to your cold-water bath in order to get
the temperature low enough for the crystals to form.
6. Calculate the concentration for each trial using the formula:
Concentration in g/100 mL = grams of salt
volume of water
x
100
Data Chart: Chart 1
Grams of salt
(same value each
time)
Volume of water
mL
4.0
6.0
8.0
12.0
16.0
20.0
Concentration
(answer 3 sig figs)
Temperature when
crystals appear Co
Lab Requirements:
1.
On a piece of graph paper, construct a graph of solubility (concentration in g/100 mL) vs.
temperature. Plot points, and then draw the best curve line that you can. Draw these points as
dots, with circles around them. Complete all of this in pencil. The values that you are plotting
here for concentrations are what we will later consider to be the actual values.
2.
On the same piece of graph paper, plot the following points in the chart below, and then draw the
best curve line that you can. Draw these points as dots with squares around them. Complete all
of this in pen or marker. The values that are plotting here for concentrations are what we will
later consider to be theoretical values.
Chart 2 – Theoretical concentrations used to construct a graph
Concentration (g/100mL)
204
166
135
110
85
64
47
32
21
3.
Temperature Co
90
80
70
60
50
40
30
20
10
Complete the following chart. Notice that you will be using your temperatures to find the
theoretical values for concentrations. The concentrations from the chart in #2 are to be used to
make the graph only – do not use those values in the chart below. You need to use your
temperatures to find the corresponding theoretical concentrations.
Chart 3 – a comparison of actual concentrations to theoretical concentrations
Temperature (your
temperatures from Chart 1)
Actual Concentration
(from Chart 1)
Theoretical Concentration
(determine from the graph)
4.
Perform 6 % error calculations on the back of your graph paper. Calculate the % error in
concentration at each temperature recorded in Chart 3.
5.
Staple the graph paper to this paper. Make sure that the front of this paper faces up and the graph
faces up as well.