DATE _____________
NAME ______________________
PARTNERS: _________________________________
Experiment:
Solubility as Function of Temperature for KNO3 & NH4Cl
PURPOSE:
1. Explore the effect of temperature on the solubility of potassium nitrate, KNO3, & ammonium
chloride, NH4Cl.
2. Construct solubility graphs for bpth salts & compare them with handbook data.
INTRODUCTION:
The maximum amount of solute that will dissolve in a given amount of solvent is called
its solubility. Factors determining the solubility of a substance are:
- the identity of the solute & the solvent.
For example, sodium iodide is more soluble than sodium chloride in a given amount of water.
The identity of the solvent also affects the solubility of a substance. Sodium chloride is highly
soluble in water but not very soluble in ethanol. In general, ionic compounds are soluble in
water, but not in non-polar solvents.
- Temperature is another factor affecting solubility.
Here you will study the relationship between the solubility of potassium nitrate & ammonium
chloride in water as function of temperature. Different amounts of each salt will be dissolved in
a given amount of water at a temperature close to its boiling point. You will observe each
solution as it cools & note the temperature at which crystallization occurs. Crystallization
indicates a saturated solution, i.e. one that contains the maximum possible amount of each salt in
that amount of water. From these data, solubility graphs will be constructed & your data
compared to reference one.
MATERIALS:
8 test tubes 5 mL
thermometer
graduated cylinder
distilled water
Balance
test tube rack
hot plate (or Bunsen burner with ring stand)
400 mL beaker
KNO3
NH4Cl
stirring rod
test tube holder
Weighing boat
PROCEDURE:
1. Fill a 400 mL beaker three fourths full of tap water, place a thermometer in it, & heat the
water on a hot plate (Bunsen burner) until its temperature is about 90oC. CAUTION: Do not
touch the heated water/beaker with your bare skin. While you are waiting for the water to heat,
go on to Steps 2 and 3.
2. Place the following pre-massed amounts of KNO3 into the test tubes (take approximately
these masses but measure them precisely):
Test Tube 1: 2.0 g
Test Tube 3: 6.0 g
Test Tube 2: 4.0 g
Test Tube 4: 8.0 g
Place the following pre-massed amounts of NH4Cl into the test tubes:
Test Tube 5: 3.5 g
Test Tube 6: 3.0 g
Test Tube 7: 2.5 g
Test Tube 8: 2.0 g
3. Add 5.0 mL distilled water to each test tube.
4. Every student must be responsible for observations with one test tube at a time only. Place a
test tube holder on to test tube #1 & lower it into the hot water bath. Stir the KNO3 solution with
a stirring rod until the solid is completely dissolved. Remove the stirring rod & rinse it off.
Using a test-tube holder, remove the test tube from the bath & place it in the test tube rack.
5. Place the warm thermometer from the hot water bath into test tube 1 while the other students
repeat step 4 for test tube 2 to 8.
6. Each student should watch their test tube for the FIRST signs of crystallization (it usually
occurs around the bottom of the test tube, especially around the bulb of the thermometer. If
crystallization occurs too rapidly to observe, you can re-dissolve the salt by placing the test tube
back in the water bath and repeating the step). When it occurs, record the temperature in your
data table.
7. Place all the test tubes back in the hot water bath & re-dissolve the solid. Flush the solutions
down the drain with plenty of water. Turn off your hot plate. Clean up your glassware & work
area & wash your hands. Be sure to collect your other lab partners’ data.
DATA & OBSERVATIONS:
Data Table
Test Tube #
1
2
3
4
5
6
7
8
t 0C of
crystallization
Calculated
Solubility,
g/100mL
water
DATA ANALYSIS:
1. For EACH test tube, determine the solubility of KNO3 in grams per 100 g H2O (HINT:
recount from the amountof water in test tube, i.e. 5 mL, to 100 mL, i.e. x20)
2. Construct solubility curves for each salt by graphing the mass of salt per 100 grams of water
(solubility) versus temperature (0C). Place temperature on the x-axis & solubility on the y-axis.
Connect the points in a smooth graph.
3. Describe in words the qualitative relationship between the solubility & the temperature of the
solution.
4. Using your graph, determine how many grams of KNO3 & NH4Cl can be dissolved in 100 g
of water at the following temperatures:
A. 350C
B. 600C
C. 700C
5. Using your graph, predict whether the following solutions of KNO3 would be considered
saturated, unsaturated or supersaturated.
A. 75 g of KNO3/100 g H2O at 400C
B. 60 g of KNO3/100 g H2O at 500C
C. 75 g of KNO3/50 g H2O at 650C
Grading Rubric for Solubility Curve of KNO3
Table of Contents
1 pt.
Date, Title, Pages numbered
1 pt.
Purpose
1 pt.
Procedure
1 pt.
Data and Observations
Quantitative 2 pts.
Qualitative 2 pts.
4 pts. total
Data Analysis
#1) ½ pt. Each=2 pts.
11 pts. total
#2) Graph = 5 pts. total
(Don’t forget:
Title, axis labeled, correct plots (geometric shape
around points plotted), best fit curve, data is
spread out etc. Refer to handout from beginning of the year
titled “Effective Graphing”)
#3) 1 pt.
#4) ½ pt each.=1.5 pts. total
#5) ½ pt each=1.5 pts. total
Conclusion
CEI
C=2 pts. E=2 pts. I=2pts.
6 pts. total
________________________25 point lab
estimated min. 120