1. Name: ___________________ ( ) Class: 2A
Acid and Alkali
Name: ___________________ ( )
Class: 2A
Materials required per student:
Universal indicator
2 pcs of filter paper
3 pcs droppers (labelled 1,2 and 3) – to save time on washing up between steps
1 Test tube
Dilute HCl
2M NaOH
Sample X (2M HCl)

2. Acid rain Acidic gases dissolve with water droplets in clouds2
Acidic gases dissolve with water droplets in clouds 3
Water droplets falls as acid rain 1
Acidic gases such as sulfur dioxide and oxides of nitrogen released into the air

3. Acid Rain Effects: Acidification of soil, ocean and sea
Soil becomes acidic and affects growth of plants
Sea creatures affected as sea and ocean becomes acidic
Corrode buildings made of metal and calcium carbonate
Loss of heritage buildings

4. Colour of universal indicatorpH
pH is a measurement of solution to determine if it is acid, alkali or neutral.
Teacher’s demo with Universal indicator:
Solution
Colour of universal indicator pH
Acid
red
1-3
Alkali
blue
10-12
Water
Green
7-8

5. Acid and Alkali
Place a piece of blue litmus paper and red litmus paper on a clean filter paper.
Using dropper 1, place a drop of hydrochloric acid on both strips of litmus papers.
Record your observation:
Blue litmus paper: turns red
Red litmus paper: remains the same
Clean filter paper is used instead of white tile to save time on washing up for next step

6. Acid and Alkali
Place a piece of blue litmus paper and red litmus paper on a clean filter paper.
Using dropper 2, place a drop of sodium hydroxide on both strips of litmus papers.
Record your observation:
Blue litmus paper: remains the same
Red litmus paper: turns blue

7. Acid and alkali
pH 1-6: Acid
pH 7: Neutral
pH 8-14: Alkali

8. Acid and alkali Universal indicator Litmus paper test 1 2 3 4 5 6 7 8
orange/
yellow
red
blue
purple
green 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Acid
Neutral
Alkali
Turn blue litmus paper red
Turn red litmus paper blue
Litmus paper test

9. Scenario Imagine you are an environmental consultant.
Farmer Bob has a farm which has been experiencing poor plant growth over the past 2 years.
He decided to consult you regarding this.

10. Identify problem
You have been provided Sample X, a sample of the soil from the farm.
Conduct necessary tests to determine the problem.
Sample X: 2M HCl

11. Identify problem
Place a piece of blue litmus paper and red litmus paper on a clean tile.
Using dropper 3, place a drop of Sample X on both strips of litmus papers.
Record your observation:
Blue litmus paper: turns red
Red litmus paper: remains the same
Conclusion: The soil is * acidic/alkali (circle the correct answer)

12. Recommendation
Farmer Bob should add alkali solution to gradually increase the pH of the soil to pH 7.
This process is called neutralisation.

13. Neutralisation
Using a syringe, add 1 ml of soil sample X into a test tube.
Put 2 drops of Universal indicator.
(Colour of Universal indicator: ____red___)
Shake the test tube.
Using a dropper, add sodium hydroxide drop by drop until it changes colour. Shake the test tube after every drop.
After it changes colour, allow it to stand for 2-3 minutes.
X: 2M HCl
2M NaOH

14. Neutralisation
Results: No of drops needed: ____ Observation: Universal indicator changes colour from _red_ to __blue__. After a few minutes, it changes colour to _green_. Conclusion: Soil sample change from ___1-3___ to ____7____.
About 20 drops

15. Conclusion
For every 1 ml of soil, Farmer Bob should add ____ drops of sodium hydroxide to neutralise the soil.