An Overview of Class 12 Biology Collection Of Water From Different Water Bodies And Study Of Ph Experiment
Everything around us has a pH like pH of lemon is 2, pH of blood is 8.
Table of Contents
Aim
Apparatus Required
Theory
Procedure
Observation
Result
Precautions
Lab Manual Questions
Viva Questions
Practical Based Questions
Summary
Frequently Asked Questions
Aim
To study pH and find the presence of organisms in water bodies.
Apparatus Required
Water samples from ponds and lakes.
Test tubes
Slides
Compound Microscope
FAA(Formalin Aceto Alcohol)
pH paper strip
Beakers
Theory
Numerous plants and animals that live in water have special adaptations that help them thrive there. Turbidity, pH, and the variety of plants and animals, as well as their density, are a few of the factors that affect the quality of water. Acidic solutions are those with a pH under 7, and basic solutions are those with a pH over 7. At 25°C, pure water has a pH of 7. A pH metre can be used to calculate the pH of a water sample using the indicator dye method and the electrometric method.
Procedure
pH
Fill two clean beakers with a small amount of water from each sample, and then label the beakers A and B.
Place a little piece of paper with a wide pH range in each sample of water.
Compare the colour of the pH paper strip to the chart of typical pH values. This provides a rough pH.
Once more, compare the pH scale of the pH paper with the colour of the paper.
This will provide the accurate pH value for the water samples.
To Detect Presence of Organisms:
Collect the water samples.
Add 5 ml of FAA.
Leave the sample for 48-72 hours.
Transfer the sediments deposited into test tubes and label it.
From the test tube transfer a drop of samples to the slides and fix it in the compound microscope.
Observe the slides from lower to higher magnification.
Observation
With the colour change of the pH paper strip ,the pH of the water samples are identified.
Different types of organisms present are recorded.
Result
A natural solution's pH value of 7 indicates that the water sample is neutral.
Water samples are considered to be alkaline if the pH of a basic solution is more than 7.
Water samples are acidic by nature if the pH of an acidic solution is lower than 7.
Different organisms are identified and observed.
Precautions
Use test tubes or beakers that are dry and clean for your investigations.
Use a different dropper for each sample of water.
Let the pH paper dry completely before comparing the colour to the colour wheel.
Carefully match the hue and precisely calculate the pH.
Carefully handle the microscope.
Lab Manual Questions
1. Why do you find few organisms in polluted water.Explain.
Ans:Polluted water can lead to destruction of organisms by spreading diseases from one organism to another.So few organisms are found in polluted water.
2. Why is the FAA added after collecting the water sample?
Ans:FAA is used in water samples for the preservation of organisms present in the sample.
3. Name at least one phytoplankton and zooplankton commonly found in polluted water.
Ans:Phytoplankton found in polluted water-blue green algae,diatoms.
Zooplankton found in polluted water-protozoans,tiny fish.
Viva Questions
1. Why water is necessary for living organisms?
Ans: Plants need water for photosynthesis(process of making their own food)and animals need water for metabolic processes.
2. What are the water bodies around us?
Ans: Oceans,lakes,rivers,seas,glaciers are the water bodies around us.
3. What type of microorganisms are found in pond water?
Ans: Bacteria,microalgae,protozoans are microorganisms found in pond water.
4. What do you mean by pOH?
Ans: Potential of hydroxide ion is used to measure hydroxyl concentration in a solution.
5. What is the pH of an acidic solution?
Ans: Below 7.0 in a pH scale is an acidic solution.
6. What is the effect of dilution on the pH of an alkaline solution?
Ans: When an alkaline solution is diluted,oh ions concentration will decrease.Thus pH of alkali decreases.
7. Define pH.
Ans: pH is the measure of concentration of hydrogen ions in a solution.
8. What does the pH of a solution signify?
Ans: pH of a solution signifies the acidity or basicity of a solution.
9. Who invented pH?
Ans: In 1909,Sorensen invented the concept of pH.
10. Organisms live between which pH range?
Ans: Most organisms live between 6.5-.5 pH range.
Practical Based Questions
The pH of pure water is neutral,the best explanation for this is
The pH of pure water is 7
In pure water the concentration of hydrogen and hydroxide ions are same
Water do not contain free hydrogen and hydroxide ions
Water will never ionise.
Ans: B.In pure water the concentration of hydrogen and hydroxide ions are same.
2.The normal pH of blood is
A.7.0
B.7.2
C.7.3
D.7.4
Ans: D.7.4
3.Which of the following is an example of an amphoteric molecule?
A. Acetic acid
B. Malic acid
C. Sugars
D. Water
Ans: D. Water
4.What is the full form of pH?
A.Positive hydrogen
B.Potential hydrogen
C.Positron
D.Proton of hydrogen
Ans: B.Potential hydrogen
5.In presence of an acid,amino group can be
A.Polarized
B.Washed away
C.Protonated
D.Replaced
Ans: C.Protonated
6.Why does ice float in water?
A.Because of stronger hydrogen bonds at the surface
B.The density of water as a solid is less than the density of water as a liquid
C.Surface tension helps it float
D.It is more dense
Ans: B.The density of water as a solid is less than the density of water as a liquid
7.Pollution causes the pH of rainwater to fall below 6.What is such type of rain called?
A.Acid rain
B.Polluted rain
C.Low pH rain
D.Non point source pollution
Ans: A.Acid rain
8.According to the pH range which substance is more acidic than lemon juice.
A.Hydrochloric acid
B.Cabbage
C.Milk
Ans: A.Hydrochloric acid
9.Upper part of sea/aquatic ecosystem contains:
A.Plankton
B.Nekton
C.Benthons
D.None of the above
Ans: A.Plankton
10.The second trophic level in a lake is
A.Fungi
B.Benthos
C.Zooplankton
D.Phytoplankton
Ans: C.Zooplankton
Summary
The pH of the two different water samples are identified using a pH paper strip.
The organisms in the water bodies are identified using a microscope.
FAQs on Class 12 Biology Collection Of Water From Different Water Bodies And Study Of Ph Experiment
1. What are the important steps to follow for the Class 12 experiment on collecting and studying water from different water bodies?
For this experiment, you should follow a clear procedure to ensure accurate results. The key steps are:
- Collection: Use clean, separate glass bottles to collect water from at least two different sources, like a pond and tap water. Label each bottle clearly.
- pH Testing: Take a small amount of each sample in a separate test tube. Add a few drops of universal indicator solution or dip a strip of pH paper. Match the resulting colour with the pH chart to find the pH value.
- Observing Organisms: Place a drop of a water sample on a clean glass slide. Gently place a coverslip over it. First, observe it under a low-power microscope and then switch to high power to identify different microorganisms.
- Recording: Note down the source, pH, clarity, and types of organisms seen for each sample in your practical notebook.
2. What are some expected questions a student might face in a viva for this experiment for the 2025-26 practicals?
In a viva voce, the examiner tests your understanding of the concepts behind the experiment. Be prepared for questions like:
- What is the normal pH range for drinking water? (Usually 6.5 to 8.5)
- Why did you choose these specific water bodies for comparison?
- What is the role of a universal indicator?
- Name one protozoan and one alga you might find in pond water.
- What precautions did you take to avoid errors?
3. What do different pH levels in water samples indicate about their quality?
The pH level is a crucial indicator of water quality. A neutral pH is 7. Water with a pH lower than 7 is acidic, which might be due to industrial pollutants or acid rain. Water with a pH higher than 7 is alkaline, possibly caused by dissolved minerals or contamination from detergents. Most aquatic organisms thrive in a pH range of 6.5 to 8.5, so extreme values suggest the water is polluted and cannot support a healthy ecosystem.
4. How can you infer the health of a water body based on the microorganisms found in it?
The variety and type of microorganisms act as bio-indicators. A healthy water body, like a clean pond, will have high biodiversity, meaning you'll find many different types of organisms like diatoms, amoeba, and paramecium. In contrast, a polluted water body may have a large population of only a few types of organisms, such as certain algae or bacteria that thrive in polluted conditions. This lack of diversity points to an unhealthy ecosystem.
5. Why is it important to observe a water sample under both low and high power on a microscope?
Observing under both powers is essential for a complete study. You start with low power to get a general overview of the sample and locate larger organisms or clusters of activity. Once you find an area of interest, you switch to high power to see the finer details of the smaller microorganisms, helping you to identify them correctly based on their shape, size, and movement.
6. What are two crucial precautions to take while performing this experiment to get reliable marks?
To ensure accuracy and get good marks in your practical exam, you must follow precautions. Two of the most important are:
- Avoid Contamination: Always use separate, clean droppers and slides for each water sample. This prevents the microorganisms or chemical properties of one sample from mixing with another, which would lead to incorrect results.
- Handle Glassware Safely: Be careful with glass slides, coverslips, and beakers. A broken slide can cause injury, and a cracked test tube can lead to inaccurate pH readings.
7. Can a water sample that appears perfectly clear still be unsafe for aquatic life? Why?
Yes, absolutely. Clarity only tells us about the absence of suspended particles like mud or debris (turbidity). A water sample can look crystal clear but have a dangerous pH level due to dissolved chemicals. For instance, acid rain can make lake water very acidic (low pH) but keep it visually clear. This acidic water is highly toxic to fish and other aquatic organisms.
