LAB: SOLUBILITY OF A SALT
Introduction:
In this experiment, the solubility of potassium nitrate in water will be studied. Different amounts of the solute will be dissolved in a given amount of water. The KNO3 will completely dissolve as the mixture is heated in a warm water bath. Each solution will be observed as it cools, and the temperature at which crystallization of the salt occurs will be recorded. The start of crystallization indicates that the solution has become saturated. At this temperature, the solution contains the maximum amount of solute that can be dissolved in that amount of solvent.
After the solubility data has been collected, the data will be plotted on a graph. A smooth curve will be drawn to connect the points. The graph will then be compared to the actual curve for KNO3 found in Appendix E (see attached).
Purpose:
To determine the effect of temperature on the solubility of a salt (KNO3 and NaNO3) in water.
Procedure:
1) Obtain 4 test tubes containing the following amounts of KNO3
#1 : 2.0g
#2 : 4.0g
#3 : 6.0g
#4 : 8.0g
2) Add exactly 5.0 mL distilled water to each test tube.
3) Fill a 400 mL beaker about three-fourths full of tap water. This will be used as a water bath. Place a thermometer into the first test tube. Place the test tube into water bath and begin heating until dissolved.
4) Stir the KNO3-water mixture with the thermometer until the KNO3 is completely dissolved. With a test tube holder, remove the test tube with the thermometer still in it.
5) Hold the test tube up to the light and watch for the first sign of crystallization in the solution. At the instant crystallization starts, observe and record the temperature.
6) Rinse the thermometer from test tube #1 in the warm water bath and then place it into test tube #2. Place this test tube into the water bath and stir until KNO3 is completely dissolved. Repeat steps 3 and 4 for this sample.
7) Repeat for remaining test tubes and record temps at which crystallization begins. If any doubtful results are obtained, the procedure can be repeated by redissolving the salt and allowing it to recrystallize.
Data:
Table 1
Test Tube # / grams of KNO3 per5.0 mL H2O / grams of KNO3 per
100. mL H2O / crystallization temperature (ºC)
1 / 2.0 g/ 5.0 mL
2 / 4.0 g/ 5.0 mL
3 / 6.0 g/ 5.0 mL
4 / 8.0 g/ 5.0 mL
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Partners:
Laboratory Evaluation Chart
What is the Purpose/Objective? [Formulating Scientific Questions - 5]
Write a paragraph which:
1) states the objective (purpose/problem)
2) define solubility
3) list other factors that affect solubility
How will I conduct the investigation? [Data Collection - 5]
Brief summary of procedure
What observations and measurements did I make? [Measuring – 5]
What did you observe (can be combined with Data Section)
Data/Graph? [Communicating Laboratory Findings - 5]
What did you observe (you may use a data table)
Tables are typed or in pen
Tables have informative title
Unit labels are on the table
Use proportions to convert data to KNO3 per 100 g H2O vs. Temperature
Graph Solubility of KNO3 in grams per 100 g H2O vs. Temperature
Conclusions and validity - List possible sources of error? [Analyzing Data - 5]
Purpose is restated
Is solubility of KNO3 (and KCl) dependent on temp? Support your statements.
Validity of conclusions, improvements included
Answer questions at the end of the lab. [Working with scientific explanations - 5]
Complete Solubility Curves worksheet
Solubility Curves for Selected Solutes
1. What is the effect of temperature on the solubility of :
a. a gas in a liquid ?
b. a solid in a liquid ?
2. Based on the solubility table provided, determine the solubility of each of the following in grams of solute per l00 g H2O :
a. NaNO3 at 10º C
b. KNO3 at 60° C
c. NaCl at 50° C
3. Based on the table, at what temperature would each of the following mixtures form saturated solutions ?
a. 140 g KI / l00 g H2O
b. 115 g NaNO3 / l00 g H2O
c. 50 g KNO3 / l00 g H2O
4. If a saturated solution of KNO3 in l00 g of H2O at 60°C is cooled to 10° C, approximately how many grams of solute would precipitate, out of solution ?
5. Plot a solubility graph for AgNO3 from the following data :
grams of solute per 100 g H2O / Temperature ° C122 g / 0
216 g / 20
311 g / 40
440 g / 60
585 g / 80
733 g / 100
Refer to your graph to answer the following :
6. How does the solubility of AgNO3 vary with the temperature of the water ?
7. Estimate the solubility of AgNO3 at:
a. 30° C
b. 55° C
c. 75° C
8. At what temperature would the solubility of AgNO3 be 275g per l00 g H2O ?
9. If l00 g of AgNO3 were added to l00 g H2O at 10° C, would the resulting solution be saturated or unsaturated ?
10. What would occur if, 325 g of AgNO3 were added to l00 g of H2O at 35° C?
modified by KZ, 2014