DATE ______NAME ______

PARTNERS: ______

Experiment:

Solubility as Function of Temperature for KNO3 & NH4Cl

PURPOSE:

1. Explore the effectof 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 graphswill be constructed your data compared to reference one.

MATERIALS:

8 test tubes 5 mLtest tube rack400 mL beaker

thermometerhot plate(or Bunsen burner with ring stand) KNO3

graduated cylinder NH4Cl

distilled waterstirring rodtest tube holder

Balance 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 gTest Tube 2: 4.0 g

Test Tube 3: 6.0 gTest Tube 4: 8.0 g

Place the following pre-massed amounts of NH4Cl into the test tubes:

Test Tube 5: 3.5 gTest Tube 6: 3.0 g

Test Tube 7: 2.5 gTest 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 # / t 0C of crystallization / Calculated Solubility, g/100mL water
1
2
3
4
5
6
7
8

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. 350CB. 600CC. 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 Contents1 pt.

Date, Title, Pages numbered1 pt.

Purpose1 pt.

Procedure1 pt.

Data and Observations4 pts. total

Quantitative 2 pts.

Qualitative 2 pts.

Data Analysis11 pts. total

#1) ½ pt. Each=2 pts.

#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

Conclusion6 pts. total

CEI

C=2 pts. E=2 pts. I=2pts.

______-

25 point lab

estimated min. 120