First Science Practical: 2P1 - Properties of Acids and Alkalis

In this practical, we learnt about the properties of acids and alkalis, and experimented on how to tell the difference between acids and alkalis.

Here are the experiments we carried out on 6 substances, substance A, B, C, D, E and F.

1. Placed a drop of the substance onto a piece of i) blue litmus paper and ii) red litmus paper.
2. Tested the substances for electrical conductivity by putting an electrical conductivity tester into a small beaker containing the solution.
3. Added two drops of Universal Indicator into 2ml of the substance.
4. Added two drops of Methyl Orange into 2ml of the substance.
5. Added two drops of phenolphthalein into 2ml of the substance.

Here are the results:

1Ai) Turns red
1Aii) Stays red
2A) Dim
3A) Dark pink
4A) Red
5A) Colorless

1Bi) Turns red
1Bii) Stays red
2B) Very bright
3B) Red
4B) Dark Red
5B) Colorless

1Ci) Stays blue
1Cii) Stays red
2C) No light
3C) Green
4C) Dark orange
5C) Colorless

1Di) Turns slightly reddish
1Dii) Remains red
2D) Very bright
3D) Green
4D) Yellow
5D) Colorless

1Ei) Turns purple
1Eii) Turns dark blue
2E) Very bright
3E) Dark purple
4E) Orange
5E) Dark red

1Fi) Remains blue
1Fii) Turns blue
2F) Very dim
3F) Light purple
4F) Dark orange
5F) Dark red

The practical worksheet told us that methyl orange would be red at a pH of 1-4 and would change to yellow from 4-14, and phenolphthalein would be colorless at a pH of 1-9 and would become red at a pH of 9-14. Also, here are the colors that the universal indicator changes to at different pHs:












From this, we can see that substance A has a pH of 3, substance B has a pH of 1, substance C and D has a pH of 7, substance E has a pH of 14 and substance F has a pH of 11.

Thus, substance A is a weak acid, substance B is a strong acid, substance C and D is neutral, substance E is a strong alkali and substance F is a weak alkali.