Acids and alkalis, Year 7: more practice

Hydrochloric acid

HintIt is kept, much weaker, in a bottle on the school lab bench.

The whyStomach acid is hydrochloric acid, strong enough to kill many germs in food. The stomach wall is coated in mucus so that it is not damaged by it.

Alkalis

HintAcids taste sharp; these substances do the opposite and are good at lifting grease.

The whyAlkalis feel slippery or soapy and dissolve grease, which is why cleaning products often contain them. Never taste or touch unknown substances to find out.

It is far more concentrated

HintThink about how much acid is packed into each litre of liquid.

The whyConcentration means how much of the substance is dissolved in a given volume. A little acid in a lot of water is harmless, but the same acid in concentrated form can burn skin.

Green

HintThis colour sits exactly halfway along the indicator colour chart.

The whyUniversal indicator runs from red for strong acids, through orange and yellow, to green for neutral, then blue to purple for strong alkalis.

Blue

HintAlkalis do the opposite of what acids do to litmus paper.

The whyRed litmus paper turns blue in alkalis, and blue litmus turns red in acids. In a neutral solution neither paper changes colour.

Acids and alkalis look the same, so you need an indicator to show the difference

HintThink about how the two liquids appear before anything is added.

The whyMany acids and alkalis look like plain water. An indicator is a dye that changes colour to show which one you have, so you do not need to taste or touch it.

Danger to the environment

HintThe picture shows what the substance can harm if it is poured away carelessly.

The whyThis pictogram means the substance is hazardous to the environment, especially to water life. Such chemicals must be collected for disposal, not tipped down a sink.

Naked flames, sparks and heat

HintThink of the things that could set it alight.

The whyA flammable liquid gives off a vapour that catches fire easily. Bunsen burners are turned off or removed before such a liquid is used.

It poisons the body once it gets inside

HintCorrosives harm the surface; this warning is about what happens after it is swallowed or breathed in.

The whyCorrosive means it attacks skin, eyes or metal on contact. Toxic means it is poisonous if it enters the body by swallowing, breathing in or through the skin.

Rinse it under cold running water and tell your teacher

HintDilute it as quickly as you can, and make sure an adult knows.

The whyPlenty of cold running water dilutes the chemical and washes it away. Telling the teacher means help arrives and the incident is recorded.