Acid-Base test
Objectives:
- Able to identify the acids and bases
- Examine the common substance used at home based on taste and touch and classify them as acidic or basic
- Able to identify acids and bases using only one indicator
- Able to identify, differentiate and classify acids and bases by using all indicators
Materials required:
litmus paper, turmeric, Lemon juice, orange juice, curd, sugar, common salt, Amla, baking soda, vinegar, etc,
Reference links
Kalika chetharike Material, Litmus Paper test to detect Acid, Bases and Neutral substance
Process:
1. Litmus paper as indicator:
When litmus paper added to an acidic solution, it turns red and when added to a basic solution, it turns blue. It is available in the form of a solution, or in the form of strips of paper, known as litmus paper. Generally, it is available as red and blue litmus paper.
Step 1: Mix some water with lemon juice in a plastic cup/tumbler/test tube.
Step 2: Put a drop of the above solution on a strip of the red litmus paper with the help of a dropper.
Is there any change in colour?
Step3: Repeat the same exercise with the blue litmus paper.
Step 4: Note down if there is any change in colour.
Step 5: Perform the same activity with the following substances and Record your observations in the Table
| Substance | Blue/Red litmus | Change in color | Acid and base |
|---|---|---|---|
| Detergent solution | |||
| Soap solution | |||
| Shampoo | |||
| Common salt solution | |||
| Sugar solution | |||
| Vinegar | |||
| Baking soda solution | |||
| Washing soda solution | |||
| lime water | |||
| Curd | |||
| Milk | |||
| Coffee | |||
2. Turmeric as indicator :
- Take a tablespoonful of turmeric powder. Add a little water and make a paste.
- Make turmeric paper by depositing turmeric paste on blotting paper/filter paper and drying it.
- Cut thin strips of the yellow paper obtained.
- Put a drop of soap solution on the strip of turmeric paper. What do you observe?
- Similarly, test the solutions listed in the Table and note down your observations.
| Sl.no | Test solution | Effect on turmeric solution | Observations | Acid/Base |
|---|---|---|---|---|
| 1 | Lemon juice | |||
| 2 | Orange juice | |||
| 3 | Vinegar | |||
| 4 | Baking soda | |||
| 5 | Lime water | |||
| 6 | Sugar | |||
| 7 | Common salt |
3. China rose as Indicator:
- Collect some China rose (Gudhal) petals and place them in a beaker.
- Add some warm water. Keep the mixture for some time till water becomes coloured.
- Use the coloured water as an indicator.
- Add five drops of the indicator to each of the solutions given in Table
What is the effect of the indicator on acidic, basic and neutral solutions?
| S. No. | Test solution | Initial colour | Final colour |
|---|---|---|---|
| 1 | Shampoo (dilute solution) | ||
| 2 | Lemon juice | ||
| 3 | Soda water | ||
| 4 | Vinegar | ||
| 5 | Sugar solution | ||
| 6 | Common salt solution |
Acid and Base:
The word acid comes from the Latin word acere which means sour. Acids are sour in taste. Ex; Curd, lemon juice, orange juice and vinegar taste sour. Whereas, bases are bitter and soapy to touch. Substances which are neither acidic nor basic are called neutral
Special type of substances are used to test whether a substance is acidic or basic. These substances are known as indicators. The indicators change their colour when added to a solution containing an acidic or a basic substance. Turmeric, litmus, China rose petals (Gudhal), etc., are some of the naturally occurring indicators.
- Acid turns blue litmus red. Bases turn red litmus blue.
- The turmeric is acidic in nature, and it is yellow. When turmeric paste is added to the acidic solution, it remains unchanged. The colour of the acidic solution is yellow. When turmeric paste is added to the basic solution the yellow colour changes to red colour
- China rose indicator turns acidic solutions to dark pink (magenta) and basic solutions to green.
Pedagogic principles:
Using group work and experimentation to make solutions through which identifying acids and bases.
Assessment:
| Criterion | 5 | 4 | 3 | 2 | 1 |
| Infers
correctly |
Identifies the given substance as acids /bases correctly | Infers all substances correctly with one or two mistakes | Infers few substance correctly and few substances incorrect. | Requires constant help to infer substance as acids/bases | Not able to
infer |
| Follows instructions | Follows instructions correctly and do the activity | Follow instructions with minor mistakes | Follows few instructions correctly | Follows one or two instructions correctly | Cannot follow instructions |