Lab: Solubility Study (30 points)
(page 1 of 2)
Objective: Determine the solubility of an unknown salt at various temperatures and
generate a solubility curve.
Reference: Zumdahl Chapter 11 section 3
Introduction:
If a salt is soluble it means it can dissolve in a particular solvent. The solubility of a
substance can be expressed as the number of grams of the solute (the solid) that will
dissolve in 100mL of the solvent. The solvent is usually water. Handbooks of
chemical data list the solubility of various substances at a particular temperature.
Solubility changes with temperature. For example, hot tea will dissolve more sugar
than iced tea. For most substances, the solubility increases with increasing
temperature. Rather than present long lists of solubility data, this information is often
expressed as a graph. A solution that can not hold any more solute at a given
temperature is said to be saturated.
Some salts dissolve very slowly. You could classify a salt as insoluble only to find it
dissolved half an hour later. The speed a salt dissolves has nothing to do with how
much the solvent can hold. Grinding the solute to a fine powder or stirring/shaking
the mixture can increase the rate of dissolving. Such techniques don’t affect the final
amount of solute that ultimately dissolves.
Hazard for unknown salt: strong oxidant (helps things burn fast), fire and explosion
risk when heated or on contact with some organic
materials, skin irritant
Procedure:
1) Immediately begin boiling about 300mL water in a 400mL beaker. Clean a 10mL
test tube and shake it dry.
2) See your instructor for the amount of salt you are to study. It will be 5.5g, 5.0g,
4.5g, 4.0g, 3.5g, 3.0g, or 2.5g. Mass out this amount of salt on a piece of paper.
Try to get fairly close. Record the salt mass to the nearest 0.01grams and tap it in
the 10mL test tube.
3) Place the test tube and solid in a beaker and add about 3g water using a dropper
bottle. Remember 1.00g water is the same as 1.00mL water.
4) Suspend this test tube in the boiling water bath. Gently stir with a thermometer.
Minimize the time the test tube is heated to minimize evaporation of the water.
(This will goof-up the concentration of the solution.)
5) Once all solid is dissolved let the test tube cool in the air while gently stirring with
the thermometer. Record the temperature that crystals begin to form.
6) Add another gram of water and determine the solubility point of this combination.
Discard the slurry in the waste jug.
7) Calculate the mass of unknown salt that would dissolve in 100.g water. Do this
for both temperatures and record your results on the class overhead.
example: 3.21g solid
X
------------------- = ------------------3.05mL water
100.g water
8) Using the class data generate a solubility curve. Plot saturation temperature on
the horizontal axis and plot saturation mass on the vertical axis. If using
Graphical Analysis select any equation that generates a smooth curve. The
temperature scale should extend to 50’C to answer a future question.
Names in Lab Team: _______________________________________ period ______
Lab: Study of Solubility (30 points)
(page 2 of 2)
Questions: (1 points each)
1) What is the solubility of the following salts in 100g water at 50’C?
Na2SO4 ________
KCl _______
2) Define saturated solution.
KBr _________
3) Define solubility.
4) Does stirring affect salt solubility or the rate that a salt dissolves?
5) Generally how is solid solubility affected by higher temperature?
6) Generally how is gas solubility affected by higher temperature?
7) Why is better to determine saturation temperature when the temperature is
dropping rather than when the temperature is rising?
8) Why was it wise to minimize the heating of your solution?
9) The solubility of your unknown salt at 50’C should be 90g/100mL water. What is
the solubility of this salt at 50’C from your graph?
10) Show a smooth calculation for % error.
Date Table One
(10 points)
amount of solid
added
total amount of
water added
saturation
temperature
saturation grams
per 100mL water
Summary:
lower water volume
study
larger water volume
study
accuracy
+ 0.01g
+ 0.01mL
+ 0.1’C
significant
figures (?)
Submit the data table one (10 points)
Submit answers to questions (12 points)
Submit plot of mass per 100mL water vs saturation temperature (8 pts)
Lab: Solubility Study
Date Table Two: Class Data
saturation
mass solid per
temperature 100mL water students in lab team
period