Neither red nor blue
Some liquids leave both strips just as they were.
What about water?
Plain tap water has no sour taste and no soapy feel.
Is tap water an acid, a base, or something else?
What this lesson covers
The idea
Substances that change the colour of neither blue nor red litmus are neutral, because they are neither acidic nor basic.
What about water?
Plain tap water has no sour taste and no soapy feel.
Is tap water an acid, a base, or something else?
- An acid
- A base
- Neither of them
Hunt for no change
Test each liquid with both strips. Look for liquids where neither strip changes colour.
Neutral
Three kinds of liquid, three patterns:
Substances that change the colour of neither blue nor red litmus are neutral. They are neither acidic nor basic.
Tap water, sugar solution and salt solution are neutral.
- Kind of liquid | Blue litmus | Red litmus
- Acidic | turns red | stays red
- Basic | stays blue | turns blue
- Neutral | stays blue | stays red
Notes
Substances that change the colour of neither blue nor red litmus are neutral, because they are neither acidic nor basic.
Check yourself
A liquid does not change blue litmus and does not change red litmus. It is...
Which two liquids are both neutral?
Blue litmus stays blue in a liquid. Why can we not yet say the liquid is neutral?
Red litmus turns blue and blue litmus stays blue in a liquid. The liquid is...
- neutral — correct. Yes! It is neither acidic nor basic.
- acidic. An acid would turn blue litmus red.
- basic. A base would turn red litmus blue.
- Lemon juice and salt solution. Lemon juice is acidic. It turns blue litmus red.
- Soap solution and tap water. Soap solution is basic. It turns red litmus blue.
- Tap water and sugar solution — correct. Yes! Neither changes either strip.
- It also stays blue in a base. Test red litmus too. — correct. Yes! You need both strips: only when both stay unchanged is the liquid neutral.
- Blue litmus is never reliable. Blue litmus is reliable, but it only tells us about acids.
- Because the strip is still wet. Wetness has nothing to do with it.
- neutral. A neutral liquid would change neither strip. Here the red strip changed.
- acidic. An acid changes the blue strip, not the red one.
- basic — correct. Yes! Red turned blue, which is the sign of a base.