Acid or alkali? Acidic or alkaline?
This simple experiment involves testing a variety of substances to see if they are acidic or alkaline. Litmus paper is used as the indicator.
Read our standard health & safety guidance
Lesson organisation
This experiment is most suitable for introductory level chemistry and could be done as a circus with pairs/small groups of students moving from one ‘station’ to another.
A discussion of the meaning of the words ‘acid’, ‘alkali’ and ‘neutral’ could be a good way to introduce the experiment. The idea of an ‘indicator’ should be introduced as a means of distinguishing between the three possibilities, using litmus as the indicator.
Apparatus and chemicals
Eye protection
Each working group will require:
Red and blue litmus paper, 3 pieces of each
Access to small amounts of common everyday substances such as:
• fizzy drinks
• tap water
• de-ionised/distilled water
• toothpaste
• shampoo
• soap
• vinegar
• lemon juice
Technical notes
1 Provide small amounts of the samples on watch glasses. The watch glasses can be placed on a white tile marked with the name of the substance - use a waterproof marker.
2 The samples can be arranged around the room so that the students visit each in turn. If any solid sample is used, moisten it with a little de-ionised water.
Procedure
HEALTH & SAFETY: Wear eye protection.
a Tear each piece of litmus paper into 3 smaller pieces so that you can test at least 9 substances.
b Take one small piece of red litmus paper. Dip it into one of the substances to be tested. Repeat with a small piece of the blue litmus paper.
c Record all observations in a suitable table. Then dispose of the pieces of litmus paper in the waste bin.
Teaching notes
If:
the blue Litmus paper turns red
the red is unaffected
then the substance is acidic.
If:
the red Litmus paper turns blue
the blue is unaffected
then the substance is alkaline.
If neither red nor the blue paper changes colour, the substance is neutral.
Students should make three lists of substances under the headings ‘acidic’, ‘alkaline’, ‘neutral’.
Encourage the students to use the terms correctly. ‘Acid’ and ‘alkali’ are nouns; the words ‘acidic’ and ‘alkaline’ are adjectives. ‘A solution of vinegar is acidic. Vinegar is an acid.’
Health and Safety checked, November 2006
Updated 29 Oct 2008Average rating: 
4 out of 5
Your reviews
All good! Where can I buy the litmus paper and the liquid for testing degree of alkalinity and acidity in Perth WA?
Submitted by: joshua on 11 November 2008
It was good of you to take the time to do this.
Submitted by: jordon on 18 December 2008
It did not help me!
Submitted by: Mack on 8 April 2009
I just want to say thanks to the facilitators of this website. It's seldom that you find a site that is there to educate and not for profit.
Submitted by: Kashif Azad on 14 June 2009
You can buy materials from eBAY Australia.
Submitted by: nobody on 25 July 2009
IT HELPED ME TO SCORE VERY GOOD MARKS IN MY SCIENCE EXAM!
Submitted by: SIDDARTH on 4 August 2009
This experiment is pretty standard for year 7 or 8. What I particularly wanted to comment on was the idea for arranging the lesson - my organisation is much messier and I like the idea of watch glasses etc. Thanks very much.
Submitted by: Debbie Woodland on 7 August 2009
Some foods taste sweet,while others taste salty, bitter or sour . A lot of substances in our homes produce different colour changes when tested with litmus papers . What are litmus papers?
Submitted by: rasia on 11 August 2009
In reply to Rasia: Litmus papers come in two forms: red and blue, and are used to test whether substances or solutions are acidic or alkaline. Red litmus goes blue in alkali and blue litmus goes red in acid.
If no water is present, e.g. testing a gas or a solid, then the test paper must first be moistened.
Litmus is a dye extracted from the roots of a plant and is used in the laboratory as an indicator solution or absorbed onto paper and sold in 'booklets' of tear-off strips.
Submitted by: Faraday on 12 August 2009
Show us the answers for the result.
Submitted by: jodie on 9 November 2009
If you do not have litmus paper, you should try to use the red cabbage on your experiments. It works. TRY IT - you'll enjoy!
Submitted by: nur roshaniera on 8 February 2010
Simple and precise.
Submitted by: Leong on 7 August 2007