The shelf again
A shelf holds lime juice, soap water and salt water. Which jars are acids? A litmus strip is dye on paper that changes colour.
Step 1 of 4
- Dip a blue strip and a red strip into each jar.
- In the acid jar, the blue strip turns red.
- In the base jar, the red strip turns blue.
- In the neutral jar, neither strip changes.
Read the two strips on each card below.
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The rule
Lime juice is the acid. Soap water is a base. Salt water is neutral.
Blue turning red names an acid. Red turning blue names a base. Neither strip moving names a neutral substance.
- Acid — a substance that turns blue litmus red.
- Base — a substance that turns red litmus blue.
- Neutral — a substance that changes neither strip.
| Group | Blue strip | Red strip |
|---|---|---|
| Acid | turns red | stays red |
| Base | stays blue | turns blue |
| Neutral | stays blue | stays red |
Curd turns the blue strip red, so curd is an acid. Salt water moves neither strip, so it is neutral.
Watch out!
A blue strip that stays blue does not say neutral. Soap water keeps it blue too, and soap is a base. Only the red strip tells base from neutral.