Grades: 9-12 (Science, Chemistry and Biology)
Time: 60 minutes
Space Requirement: Classroom with sink and ample counter space
Methodology: Cooperative Learning, Group Discussion, Community Action.
Materials not included in the kit:
Water samples from your school and from up to five outside communities
Materials included in the kit that will be used:
Ammonia Test Strips, disposable beakers and ammonia colour matching charts
Objectives: Students will expand their knowledge of the problems caused by ammonia in drinking water sources. Students will investigate the quality of their local water and that of a number of samples from the surrounding area. Students will act to help any communities which are found to have improperly disinfected drinking water.
Directions/Procedure:
Begin collecting water samples from nearby communities as early as possible. Some of your students or fellow teachers may be from an outside community or planning to visit an outside community, ask them to bring in a water sample. It would be ideal to get some samples from places that get their water from different sources and treatment facilities. Samples as small as 20mL will be okay and almost any clean, well-rinsed container will do, just make sure it is labeled with the location where it was collected. Materials to test your local water plus five outside samples are provided.
Discussion of results from experiments in Lesson Four:
a. On the board draw a chart resembling the one at the end of the Lesson Four Handout that the students filled in with their experimental results. Going through each of the top nine boxes ask a few groups what concentration value they found and try to find out if there is any consensus among groups. Mark on the board a value or range of values that reflect the findings of the class.
b. Ask students to share their answer for the first of the questions posed on the Lesson Four Handout. Record a typical answer or two on the board. Demonstrate how these values can be found to any students who may need the explanation.
c. Continue asking students to suggest answers to the questions and recording them on the board. Allow students ample opportunity to explain their thought process and methods used to find their answers. Demonstrate how question 2 could be done if students had difficulty with it and try to talk them through the others.Distribute printed copies of the Lesson Five Handout to the class and read through it with them.
You can have the class split up into groups and assign each group to test one of the samples. You could also ask for volunteers and have some students do the tests in front of the class.
If the class is splitting into groups, someone from each group can collect the water sample and ammonia test materials. Each group will perform an ammonia test on their water sample using the Ammonia Concentration Test instructions.
Check the results or poll the groups to find out if anyone got a reading higher than 0.1 mg/L.
If you had any high readings students can do some investigating. They can try to contact the treatment facility to find out if the ammonia was added during treatment. If the ammonia was not added and it was in the raw water then that drinking water is not being properly disinfected and the people of that community should be informed.
If you had at least one high reading the students will probably be interested in discussing how they feel about their, or a nearby community's, water not being properly disinfected. The students may also want to discuss what it would be like to live under a boil water advisory.
This is an excellent opportunity for the students to get active in promoting safe drinking water for everyone. Further steps that can be taken are found in the "For the Teacher" section below.
Evaluation: Students can be evaluated on the work they submit from the calculations in Lesson Four. They should demonstrate the proper use of units and an understanding of how concentration measurements work. Students can be evaluated based on their participation in the class discussions on both the chlorine and ammonia reaction and the social impact of poor quality drinking water.
For the Teacher:
If the class finds ammonia in any of the samples you should have them compose a letter to the treatment facility which informs them of the concentration of ammonia that was found and asks if this ammonia is present in the raw water or is added during treatment. It may take some phone calls and further investigation to gain this information. If the ammonia is in the raw water then it is cause for concern because this prevents proper disinfection. The class can try to get in contact with the treatment facility again to ask if they are aware of this problem and how they might be able to address it. Students may also want to write to their MLA to inform them of the situation. The Safe Drinking Water Foundation would like to know if classes are taking this sort of action so please keep us updated by sending an e-mail to info@safewater.org
Answer Key for the questions on the Lesson Four Handout
1. The chloramine concentrations can be found by subtracting the free chlorine concentrations from the total chlorine concentrations.
2. Since the two solutions are being mixed 50/50 the concentration of each chemical in the mixed solution will initially (due to dilution before chemical reaction happens) be the average of the values in the two separate solutions as was demonstrated in the salt and sugar example. For example, if the chlorine solution had a total chlorine concentration of 0.8mg/L and the ammonia solution had a total chlorine concentration of 0.1mg/L then the computation the students would have to perform is as follows:
0.8 mg/L * 100 mL + 0.1mg/L * 100 mL = 0.09mg total chlorine in the mixed solution 0.09mg / 200mL = 0.45mg/L total chlorine in the mixed solution
Or simply
(0.8mg/L + 0.1mg/L) / 2 = 0.45mg/L
Students are expected to do four such calculations, one each for ammonia, total chlorine, free chlorine and chloramine.
Students should understand that it is the difference between these calculated concentrations and the experimentally found concentrations of the mixed solution that indicate the results of the chemical reaction and NOT the difference between the experimentally found concentrations of the unmixed solutions and mixed solution.
For example if the chlorine solution had a free chlorine concentration of 0.8mg/L, the ammonia solution had a free chlorine concentration of 0.0mg/L and the mixed solution had a free chlorine concentration of 0.0mg/L then students may be tempted to say that the chemical reaction reduced the free chlorine concentration from 0.8mg/L to 0.0mg/L. What has really happened is that the free chlorine concentration was reduced to 0.4mg/L by the dilution and then further to 0.0mg/L by the chemical reaction in separate processes.
3.
a) The expected answer is “no”, some of the experimental results should be very close to the results found in question 2.
b) It is expected that the calculated concentrations of ammonia and total chlorine will be very close to the students’ actual experimental findings. This does not, however, mean that ammonia and total chlorine were not involved in the reaction. They are, of course, very important reactants.
c) The ammonia concentration may appear to have been unaffected because its actual change would have been very small, far too small to notice with the available test. This is the case because far more chlorine is used in this reaction than ammonia. Remember that it takes about 10-15mg of chlorine to react with 1mg of ammonia.
The total chlorine concentrations may be unaffected because as the free chlorine is turned into chloramine the sum, free chlorine + chloramine should be constant.
d) It is expected that the calculated concentrations of free chlorine and chloramine will be quite different from the experimental results.
The free chlorine concentration should drop sharply since it is used in the reaction with the ammonia.
The chloramine concentration should increase accordingly since it is created in the reaction.
4. It is up to the students to decide if they believe their experimental results agree with the assumptions or not. They should be expected to be able to support and explain their answer. Ask students to compare the apparent amounts of free chlorine and ammonia that their experimental results indicate were used in the reaction.
Ask students to compare the apparent increase in chloramine concentration with the decrease in free chlorine concentration.
Related Links:
Disease Causing Micro-Organisms
www.safewater.org/fact-sheets-1/2017/1/23/disease-causing-microorganisms
IBROM Treatment System
http://www.safedrinkingwaterteam.org/ibrom.html
Nitrogen Cycle
https://www.thoughtco.com/what-is-the-nitrogen-cycle-607607
Operation Water Biology
Lesson Five
Consequences of Inadequate Drinking Water Treatment
Discovering if a community has a problem with ammonia is as simple as doing a single test on a sample of tap water but since there is no guideline for ammonia in the Guidelines for Canadian Drinking Water Quality this test is rarely done. People in these communities often do not know that their water is not being properly disinfected. In this lesson your class will perform ammonia tests on the water samples that you have collected.
Location that this water sample was collected
_____________________________________
Ammonia concentration of the water sample
_____________________________________
Your class might find ammonia in some of the water samples that you have collected and tested during this lesson. Recall from Lesson Three when you learned that some water treatment facilities add ammonia to the water. This is done after the water has been disinfected so that they can use it to create chloramine which will keep the water disinfected throughout the distribution system. In these cases the water is properly disinfected even though an ammonia test might show that there is still ammonia in the water. This practice is usually only used by water treatment facilities serving very large distribution systems and is not common in rural communities that have small facilities. If you do find ammonia in these samples you should investigate whether the facility that treated that water added the ammonia after disinfection or if the ammonia was in the raw water. Only if the ammonia was in the raw water is there cause to be concerned that the water was not disinfected. This means that there could be disease-causing micro-organisms in that water. When a situation like this is discovered a boil water advisory is usually put in effect.