Acids and alkalis
In this topic you will:
- learn about the properties of acids and alkalis
- learn how to work safely with acids and alkalis
- find out about hazard symbols.
Key words
- acid
- alkalis
- corrosive
- flammable
- harmful
- irritate
- oxidising
- toxic
Acids are everywhere
Many things contain acid. Some foods contain acid. These foods have a sour, sharp tangy taste. Lemons and limes taste sour. They contain citric acid. This is a weak acid.
Common acids in the laboratory are hydrochloric acid, sulfuric acid and nitric acid.
Some acids are dangerous
Some acids are strong. They are corrosive. The bottles have a hazard warning label. If strong acid gets onto your skin, it will dissolve the skin. You will get a chemical burn. Always use eye protection when using acids.
Acids can be diluted with water. This makes them less dangerous.
Dilute acids are still harmful, they can irritate your skin and eyes. The bottles have hazard warning labels.
If you spill acid, wash the area with lots of water. The water dilutes the acid.
Quick Fact
Even weak acids like citric acid can change the pH of a solution. That’s why lemon juice can affect how other substances behave chemically.
Questions
Show Answer
Lemons, limes, oranges, and vinegar all contain acid.
Show Answer
They taste sour and have a sharp, tangy flavor.
Show Answer
A corrosive substance can damage or destroy skin and other materials it touches.
Show Answer
Wash the affected area with plenty of water to dilute the acid.
Alkalis are everywhere
Many cleaning products contain alkalis such as sodium hydroxide, which is a compound of sodium, hydrogen and oxygen. Sodium hydroxide is a strong alkali. Strong alkalis are dangerous. They are corrosive.
If strong alkali gets on your skin, it dissolves your skin. Your skin feels soapy. You get a chemical burn. Alkalis are harmful if you get them in your eyes. Always wear eye protection when using alkalis.
Alkalis can be diluted with water. This makes them less dangerous.
Common alkalis found in the laboratory are sodium hydroxide, potassium hydroxide and calcium hydroxide.
Acids and alkalis are chemical opposites. They cancel each other out when they are mixed together. The acidity or alkalinity of a substance is a chemical property of that substance.
Working safely with acids and alkalis
When you handle chemicals you should:
- stand up to work, so that if you spill something it does not spill on to you
- wear safety glasses, so nothing gets into your eyes
- take the top of the bottle and place it upside down on the work surface, so that it does not get acid onto the surface or dirt into the acid
- replace the bottle top as soon as you have finished using the bottle. This prevents spills and reduces the risk of replacing the wrong top on the wrong bottle.
Important Concept
An alkali is a type of base that dissolves in water to form a solution with a pH greater than 7. Alkalis can neutralize acids in chemical reactions.
Hazard warning labels
Many chemicals are hazardous. Their bottles are clearly labelled with hazard warning symbols so that you know you must handle them carefully. Here is a list of the most common hazard symbols and what they mean.
| Explosive |  |
A substance that can explode if it comes into contact with a flame or heat. |
| Flammable |  |
A substance that can catch fire easily. |
| Oxidising |  |
A substance that gives off a large amount of heat when in contact with other substances. |
| Corrosive |  |
A substance that can destroy living tissue. It can cause burns. |
| Toxic |  |
A substance that can poison you. |
| Hazardous to the environment |  |
A substance that can kill or damage living things in the environment. |
| Health hazard |  |
A substance that can cause harm such as irritating your skin and eyes. |
| Serious health hazard |  |
A substance that can cause a serious problem to your health. |
When you use chemicals in the laboratory, make sure you look at the hazard symbols and listen to advice on how to use them safely.