Preparation of lime water in ACIDS AND BASES – Class 7 Science Experiment

Chapter Name: ACIDS AND BASES

Activity Name: Preparation of lime water in ACIDS AND BASES

Activity Description:

In this experiment, we will prepare lime water, which is a solution of calcium hydroxide (Ca(OH)2) in water. Lime water is an alkaline solution and can be used to test for the presence of acidic substances.

Required Items:

1. Half a beaker of water
2. Lime (calcium hydroxide) – approximately 5 grams
3. Stirring rod
4. Filter paper or funnel for filtration

Step by Step Procedure:

1. Take half a beaker full of water.
2. Add about 5 grams of lime (calcium hydroxide) to the water. Lime is the substance commonly applied to betel leaves.
3. Stir the mixture well to ensure the lime dissolves in the water.
4. Allow the beaker to stand overnight, allowing the lime to fully dissolve.
5. The next day, filter the solution using filter paper or a funnel to remove any undissolved particles. The filtrate obtained should be transparent.
6. This filtered solution is now known as lime water and can be used in various experiments related to acids and bases.

Experiment Observations:

Lime water is an alkaline solution, and its reaction with various substances can help us identify their acidic, basic, or neutral nature.

1. Substances turning blue litmus to red: These substances are acidic in nature.
2. Substances turning red litmus to blue and feeling soapy to touch: These substances are basic in nature.
3. Some substances may not cause any change in the color of either blue or red litmus; these substances are neutral in nature.

Precautions:

1. Do not taste any of the substances used in the experiment unless instructed by the teacher. Some chemicals can be harmful if ingested.
2. Clean and wash the test tubes, stirring rod, or dropper used for testing different substances on litmus paper strips before using them for the next set of experiments. Contamination of substances could lead to incorrect results.

Lesson Learnt from Experiment:

The experiment helps students understand the concept of acids, bases, and neutral substances. Lime water, being an alkaline solution, can be used as a reagent to differentiate between acidic and basic substances using litmus paper. The experiment also emphasizes the importance of safety precautions when dealing with chemicals in the laboratory.