Determining the quality of different water sources by chemical methods

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Determining the quality of different water sources by chemical methods

Chemistry

Lesson plan #3

ABOUT THE LESSON
Topic	Determining the quality of different water sources by chemical methods (experimental lesson – learning by discovery)
Duration	3 hours (3 x 45 min = 135 min)
Assumed prior knowledge	Physical properties of water. Dissolution and the factors that influence dissolution. Solubility of substances in solvents polar and non-polar. Solubility of substances in polar and non-polar (water) solvents. Solutions – preparation of aqueous solutions with known molar and percentage concentrations. Determination of acid-base character of solutions with indicators. pH of the aqueous (waterish, hydrous) solutions.
Goal(s) of the lesson	Evaluation of the consequences of processes and the action of chemical products on the person and the environment: Respect and application of personal and environmental protection rules Anticipation the effects of specific actions on the environment
The big idea behind the topic	Understanding water as a part of society and its significant role in human life. Awareness that environmental and climate changes and pollution strongly influence the lives of human beings.
Results of the lesson	Formation and developing skills to correctly handle laboratory equipment and utensils, to carry out practical determinations and to fill in observation recording sheets
Competencies	General competences: Explanation of some phenomena, processes, procedures. Investigating the behaviour of some chemical substances or systems.

Competences	Specific competences: determining the quality of some water sources to etsablish the anthropogenic impact on them; presenting the results obtained from the determination of water quality and formulation of conclusions; using of elementary working methods for the analysis of the water sample; observing the performance of experiments and the stages of their performance; using of elementary methods of recording experimental data; organizing, using and interpreting collected experimental data; formulating own observations on the analyses carried out; applying protection and security rules during the laboratory work.
Methods	Teaching methods: Heuristic / learning consolidation conversation; Explanation; Demonstration; Problematization; Brainstorming; Analysis and synthesis; Systematization, algorithmizing, modelling; Direct and guided discovery; Laboratory experiment. Forms of activity: Frontal – for communicating / updating knowledge; Individually / in teams – for experimental activities.
Relevance to the curriculum	Awareness that environmental and climate change and pollution strongly influence the lives of human beings. Possible and / or useful connections to Biology part, Physics, and Sensors Sampling Communications Modules.
Stakeholder involvement	Independent school activity (general situation). Possible assistance or/and support and connected activities during Chemistry disciplines classes (in own school or at partner schools) or thematic activities in local Scientific Centres (if available).

EQUIPMENT AND MATERIALS NEEDED

For 1 team of 5 students

Item	Quantity	Remarks
Computers (in school labs), with Internet access	1-2/team (1/student, if available)	Other available IT equipment can be used (laptops, tablets, mobile phones), with Internet access The lesson is experimental, so it should be organized in a chemistry laboratory, or in a classroom offering the necessary facilities.
Tweezers	1-2/team
Pipettes	1-3/team
Stopper glass flasks (150 ml) with water from different sources	3/team
White porcelain plates	1-3/team
Test tubes	3/team
Acid-base indicator solutions	To be established for each team
pH indicator paper	To be established for each team
pH-digital meter	1/team

This is a recommended list:

Observations

In each class / lab, 1-2 blackboards or whiteboards (magnetic and/or interactive), and a flipchart (if possible), with chalk or markers to write on, will be available.
Teachers will offer students necessary informative and practical support (experimental activities worksheets, electronic presentations, online thematic images, videos, and tutorials).

STEP-BY-STEP ACTIVITIES
Step 1 (5 min)	Organizational moment (checking presence, capturing attention, preparing didactic materials, verifying and correcting students' homework, etc.).
Step 2 (10 min)	Updating the previous knowledge necessary for teaching / experimental activity. Students are asked to respond at the following questions: What are natural waters? (examples) What are the physical-chemical characteristics that give indications about a natural water if it is polluted? (examples)

Step 3 (30 min)	Presentation and execution of the first experimental task – determination of the water quality from different sources, collected on the me day, based on organoleptic properties: students receive the worksheet with the experimental topic, analyse it, pay attention to the teacher's suggestions and explanations about their concrete experimental activity; the distribution of materials takes into consideration the number of teams in the class (preferable a multiple of 3) – each group of 3 teams receive 3 stoppered glass flasks with water from the sources indicated below: team 1: test tube 1 – drinking water, test tube 2 – water from a nearby/accessible lake or pond, test tube 3 – water from a well team 2: test tube 1 – drinking water, test tube 2 – water from a nearby/accessible river, test tube 3 – spring water; team 3: test tube 1 – drinking water, test tube 2 – water from rusty installations, test tube 3 – mineral water. Experiments analyse: 1.1. The colour of the water (gives indications of the change in its quality). 1.2. The smell of water (comes from the substances it contains, as a result of pollution or of the development of plankton). 1.3. The taste of drinking water. Interactive activity: students answer in turn to the questions formulated by the teacher, ask directions and indications regarding their experiment, fill in the data sheets with their results, and receive feedback for their work.
Step 4 (30 min)	Presentation and execution of the second experimental task – determining the acid-base character of water: students receive the worksheet with the experimental topic, analyse it, pay attention to the teacher's suggestions and explanations about their concrete experimental activity. Experiments analyse: 2.1. Determination of the medium (acid, neutral, basic) of the drinking water (the standard sample) using litmus solution. 2.2. Determination of the pH of each sample using with indicator paper. 2.3. Determination of the pH of each sample using the portable pH-meter. Interactive activity: students answer in turn to the questions formulated by the teacher, ask directions and indications regarding their experiment, fill in the data sheets with their results, and receive feedback for their work.
Step 5 (10 min)	Presentation of the results of each team with similar water samples.
Step 6 (4 min)	Formulation of conclusions according to the 2 categories of experiments carried out. Feedback through short questions and answers related to the new knowledge and the correct results of the experimental tasks. Filling in a K-W-L (Know-Want to know-Learned) table or diagram (if necessary / applicable).
Step 7 (1 min)	Final conclusions: specifying the homework (if necessary / applicable). oral or/and written appreciation (grades), after the evaluation of the experimental worksheet.
Assessment	Oral current check Systematic observation of students Students who answered and showed interest, dedicated work, and seriousness in solving the given topics can be appreciated and marked with grades.
Useful links	English: https://www.sciencebuddies.org/best-water-science-experiments https://teachbesideme.com/water-science-experiments-activities/ https://www.sciencebuddies.org/blog/teach-water-cycle-lessons 37 Water Science Experiments: Fun & Easy: https://www.educationcorner.com/water-science-experiments/ 50 Science Experiments With Water Your Kids Will Love: https://rediscoveredfamilies.com/science-experiments-with-water/ 40 Simple Water Science Experiments for Kids: https://www.lookwerelearning.com/simple-water-science-experiments/ Fantastic feats: experimenting with water: https://www.scienceinschool.org/article/2021/fantastic-feats-experimenting-water/ Romanian: https://timurovets.com/ro/30-de-experimente-usoare-cu-apa-pentru-copii-little-bins-for-little-hands https://creativesaplings.com/ro/50-de-experimente-stiintifice-usoare-pe-care-copiii-le-pot-face-acasa-cu-lucruri-pe-care-le-aveti-deja/ Experiments and STEM activities with water: https://www.youtube.com/watch?v=UtwvYMom-94

EXPERIMENTAL WORKSHEET

I. Determination of the water quality from different sources based on organoleptic properties

For the following experiments, the distribution of materials takes into consideration the number of teams in the class (preferable a multiple of 3) – each group of 3 teams receive 3 stoppered glass flasks with water from the sources indicated below:

team 1: test tube 1 – drinking water, test tube 2 – water from a nearby/accessible lake or pond, test tube 3 – water from a well
team 2: test tube 1 – drinking water, test tube 2 – water from a nearby/accessible river, test tube 3 – spring water;
team 3: test tube 1 – drinking water, test tube 2 – water from rusty installations, test tube 3 – mineral water.

1.1. The colour of the water gives indications of the change in its quality:

drinking water is colourless;
brown- or copper-coloured waters come from coal distilleries;
dark-brown waters come from pulp factories;
iron ions give the water a rusty colour;
copper ions determine a blue colour;
waters containing clay have a yellow-brown colour.

Working method

The colour is appreciated by looking at the water in each flask (made of transparent glass and containing the same amount of water, from three different sources, collected on the same day).

Recording the results: fill in the following table.

Sample number / Water source	Observed colour	Substances that can give the observed colour

1.1. The smell of the water comes from the substances it contains, as a result of pollution or as a result of the development of plankton.

Working method

Shake the water in flask 1, remove the stopper and smell. Do the same with flasks 2 and 3. Fill in the following table.

The identified smell could be described using the terms:

aromatic;
of mud;
of rotten wood;
of fish;
of hydrocarbons;
of hydrogen sulphide/sulphuretted;
of feces;
undefined;
odourless.

The odour intensity could be described using the terms:

very weak;
weak;
perceptible;
pronounced;
very strong.

Recording the results: fill in the following table.

Sample number / Water source	Identified smell	Odour intensity

1.3. The taste of the drinking water could be appreciated using the terms:

acidic;
salty;
bitter;
salty-bitter;
sweet;
sour;
special;
tasteless.

Working method

Put water from the flask marked with "1" into the disposable cups. Hold each of you 15 ml of drinking water in your mouth for a few seconds, then estimate its taste using one of the above terms.

Recording the results: fill in the following table, for member of the team.

Student	Perceived taste
1.
2.
3.
4.
5.
The taste with the highest share in the team:	…….

II. Determination of the acid-base character of water

2.1. Determination of the medium (acid, neutral, basic) of the drinking water using litmus solution

Principle of the method

Drinking water from the test tube is used as a standard sample.

The medium of each sample (acid, neutral, basic) is determined using litmus solution, and the pH is determined using indicator paper.

Utensils: litmus solution, pH indicator paper, white porcelain plate, tweezers, test tubes, pipettes.

Working method

Place half of each water sample in the empty test tube marked with the same number.

Put a few drops of litmus in each sample of water.

Recording the results

Compare the colour with the data in the following table:

Indicator	Acid medium	Neutral medium	Basic medium
Litmus	Red colour	Purple colour	Blue colour

Record the medium you determined for each sample in the table bellow:

Sample	Determined medium
1
2
3

2.2. Determination of the pH of each sample using with indicator paper

Theoretical notions

The pH represents the decimal logarithm with changed sign of the concentration of hydrogen ions in a solution: pH = - log [H3O+]. Pure water has a pH equal to - log 10 - 7 = 7.

Related to their pH, solutions can be:

acidic (pH < 7);
neutral (pH = 7);
basic (pH > 7).

Working method

Use test tubes without litmus as samples. Insert with tweezers, in each water sample, a 1 cm piece of indicator paper corresponding to the previously discovered medium. Fix the indicator paper on the white plate, compare the colour with the one on the value scale and determine the pH value.

Recording the results: fill in the following table, for each sample.

Sample	pH value	Determined medium
1
2
3

2.3. Determination of the pH of each sample using the portable pH-meter

Principle of the method

By inserting the electrode into the water sample, a potential difference appears that varies linearly with the pH of the water.

Necessary materials: pH-meter with the appropriate electrodes, Berzelius glasses, water samples.

Working method

First of all, the device is calibrated. Then the electrode is washed with distilled water and rinsed with the water to be analysed. The pH is read directly on the indicator on the device. The temperature of the sample must be 20 0C with variations of ± 0.5 0C.

The determination is repeated two more times, and the three determinations are averaged to obtain the pH value.

The determination is also repeated for different water samples.

Recording the results: fill in the table bellow.

Water sample	pH (value 1)	pH (value 2)	pH (value 3)	pH (average value)
1
2
3

Erasmus+ Cooperation partnerships project

Sailing Into Opportunities

No. 2023-1-LT01-KA220-SCH-000161306

Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the National Agency. Neither the European Union nor National Agency can be held responsible for them.

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