Water Pollutant Solubility and Mixture Lab
Your CSI team has been asked to determine how some of the following possible pollutants may be able to dissolve in water or oils, OR be transported via flotation or emulsification on top or within of a water body in a watershed. Your team should choose two solid contaminants and two liquid contaminants to test and compare in terms of either solubility or emulsification. Your team should find a reasonable solubility amount in g/ml for each of the possible contaminants and then compare to find out which of them is most likely to be transported farther and contaminate more of a watershed. Then, you should determine how well two of the liquids can emulsify in water and what effect the presence of a specific emulsifier/surfactant may have in changing the ability of the liquid to be emulsified and therefore transported via a watershed.
Potential water pollutants:
A. Solids: (determine the maximum solubility)
Fertilizers: Miracle Gro (N-P-K) Percentage of Nitrogen, Phosphorus, Potassium
Acids: Citric Acid
Metallic Compounds: Iron Chloride
Copper Chloride
Copper Sulfate
Aluminum Potassium Sulfate
B. Liquids: (determine emulsification)
Insecticides: Orange oil (orange guard)
Hydrocarbons: Cooking oils (olive, canola, vegetable oils)
Mineral oil
Motor oil
Surfactants that may change emulsification: Dishwashing liquid (Dawn)
Mustard powder
Part A: Solubility Procedure:
1. SAFETY First: Wear safety glasses/goggles at ALL times when working with or handling the chemicals in this lab.
2. Choose two (2) of the potential solid contaminants from the list to compare their solubilities.
3. Measure 15 mL of distilled water into a test tube with a sealable cap.
4. Measure 1 g of the first solid to be tested into the test tube. For each successive trial add one additional gram of the solid.
5. Cap the test tube tightly and agitate by shaking for 20 times up and down over a 10-15 second period of time.
6. Allow tube to settle for 30 seconds.
7. Observe tube, noting if all of the solid has dissolved.
If so, then continue and repeat.
If not, then shake once again for 20 times in 10-15 seconds.
If solid still remains, then STOP and record the solubility as the MAXIMUM amount of the solute that COULD be dissolved WITHOUT solid remaining in the bottom of the test tube. Record the values for this on the chart provided.
8. Repeat this procedure for the other solid(s) solute pollutants.
9. Dispose of the chemical solutions as directed by your instructor.
10. Clean up tubes and other apparatus and return to appropriate locations.
11. Complete analysis and conclusion questions for this section of the lab.
Solubility Testing Table:
Grams of solute added: / Solubility test table: STOP when solid first remains in tubePollutant 1: / Pollutant 2:
All solid dissolved? Y or N / All solid dissolved? Y or N
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Part A Analysis:
1. Record the MAXIMUM amount of solute pollutant that was able to dissolve for EACH of the solids tested, then estimate the solubility based on the amount of solid remaining in the tube after the last trial.
Solid Pollutant Name: / Maximum Amount dissolved: / Estimated Solubility:2. Which of the solid pollutants tested had the highest estimated solubility?
3. How is having a higher solubility related to the potential pollution that this solid could produce in a watershed?
4. What factors could affect how much of these solids gets dissolved in the water in a watershed? (i.e. what factors could affect their solubilities?)
5. If these two solids are spilled near a watershed, what recommendations would you make based on your results?
Part B: Liquid emulsification Procedures:
Background: When liquids are spilled near a watershed, many are non-polar (such as oil) and will not dissolve in water. However, many of these liquids will form emulsions with water when surfactants or emulsifiers are present, thus allowing them to be transported within the runoff water from the location of the spill. The emulsification depends not only on the liquid, but also on the amount of agitation and the presence of these surfactants or emulsifiers. In this activity, you will investigate how the presence of certain surfactants may increase the time that non-polar liquids can remain emulsified and thus possibly cause pollution in larger areas of a watershed.
Surfactants (surface active agents) are often utilized in the emulsification process. A surfactant can be considered a “confused” molecule having both a hydrophobic (water-hating) and hydrophilic (water-loving) part. Because of this, many surfactants are said to “make water wetter”. They include detergents, soaps, some acids and mixed compounds. All of these will lower the surface tension of water, thus making it easier to remove contaminants and also temporarily stabilizing the emulsion making it last longer. Surfactants essentially lengthen the amount of time it takes to separate two phases of liquids (polar and non-polar like oil and water). Some surfactants work better for certain types of liquids and will lengthen the emulsification time of the liquids depending on the amount and type of surfactant used.
Part 1:
To learn how to conduct experiments using surfactants, you will use cooking oil, distilled water and mustard powder as the surfactant.
1. WEAR SAFETY GLASSES during all times when working with chemicals in the lab.
2. In a medium sized test tube, add 10 mL or distilled water and 10 mL of cooking oil (canola, etc.) This will be the CONTROL.
3. Shake the mixture 20 times vigorously up and down over a 15 second period.
4. Place in storage rack and IMMEDIATELY start timer to determine time to separate.
5. Observe tube carefully for “full” separation of the oil and water.
6. When the oil and water have completely separated again, record the time it took to separate in seconds in the chart.
7. Repeat two more times. Record the time, and get an average time for the control.
8. In a new tube, place 10 mL each of distilled water, cooking oil and appropriate amount of mustard powder (start with 0.1 g and increase by 0.05 g each time).
9. Again, shake the tube vigorously 20 times in a 15 second period.
10. Place in storage rack and IMMEDIATELY start timer to determine time to separate.
11. Observe tube carefully for “full” separation of the oil and water. BE PATIENT.
12. When the oil and water have completely separated again, record the time it took to separate in seconds in the chart.
13. Repeat several more times, increasing the amount of mustard powder each time.
14. Record all results in the chart.
15. Dispose of used chemicals as indicated by your instructor.
16. Clean up all equipment and return to appropriate locations when finished.
Mass of mustard powder added to oil (g) / Time for mixture to separate (seconds)Test 1 / Test 2 / Test 3 / Mean time
NONE (Control)
0.10
0.15
0.20
0.25
0.30
Part 2:
Now, it is your turn to design and complete one more experiment. In order to compare how surfactants work, you should choose one OTHER type of liquid (oil, etc.) to test and either use mustard powder or dishwashing liquid as the surfactant. Use the same type of procedure as in Part 1, but be prepared to alter the procedure in terms of amounts of substances, or time to separate depending on your choice of liquid and surfactant.
Be sure to make notes of your procedure below:
Here is a chart that may be useful if using mustard powder.
Mass of mustard powder added to oil (g) / Time for mixture to separate (seconds)Test 1 / Test 2 / Test 3 / Mean time
NONE (Control)
0.10
0.15
0.20
0.25
0.30
Analysis:
1. What combination of liquids and surfactants took the longest time to separate?
2. What effect does this increase in emulsification have on the potential for these substances to cause greater pollution in the watershed?
3. Based on your results, what combination of liquids and surfactants pose the greatest risk of pollution in the watershed? Support your conclusion with examples from your data.