Acids and bases

Acids and bases

Acids are common in everyday life. Some are weak while others are strong. Many are dangerous to touch or taste. Most weak acids found in nature are quite safe to taste. They are called organic acids. See the list below.

Strong mineral acids

Strong acids are corrosive and they can eat away materials like metals and fabrics. Examples of strong mineral acids found in a school laboratory are:

Hydrochloric acid

HCl

Sulphuric acid

H₂SO₄

Nitric acid

HNO₃

Strong acids can be diluted by adding water. Most fizzy drinks contain dissolved carbon dioxide. When carbon dioxide dissolves in water it forms an acid called carbonic acid (H₂CO₃).

Acids have many uses. Car batteries, for example contain sulphuric acid (H₂SO₄). Many fertilizers are also made with the help of sulfuric acid (eg. super phosphate). Hydrochloric acid (HCl) is used to clean mortar from bricks. Hydrochloric acid in your stomach is essential for digestion. The genetic material, DNA, found in every living cell is deoxyribonucleic acid.

Ants and bees have acids

Acids on your skin sting because they are corrosive and attack your body tissues. This is why lemon juice stings if you get it in a cut on your finger. Certain types of ants and bees sting because they inject you with formic acid.

Dilute and concentrated acids

Most fruits contain acids but you can eat them because the acid in them is very dilute. A dilute acid contains large amounts of water and a small amount of acid. Some of the acids that we use at school laboratories are concentrated acids. They contain large amount of acid and very little water.

Properties of acids

Acids (weak acids) have sour taste.

They change the colour of indicators such as litmus.

They react with certain metals to form hydrogen gas.

They all provide H⁺ ions during a chemical reaction.

Multiple Choice

Taste of weak acids:

• Bitter

• Salty

• Sour

• Sweet

Multiple Choice

Weak acids found in living things are called:

• organic acid

• mineral acid

• concentrated acid

• carbonic acid

Multiple Choice

Sour milk (yoghurt) contain:

• hydrochloric acid

• lactic acid

• sulfuric acid

• nitric acid

Multiple Choice

Fizzy drinks (soda) contain:

• carbonic acid

• sulfuric acid

• nitric acid

• hydrochloric acid

Multiple Choice

Acid in your stomach is:

• sulfuric acid

• nitric acid

• citric acid

• hydrochloric acid

Multiple Choice

Lime juice and orange juice contain:

• citric acid

• ethanoic acid

• Malic acid

• Lactic acid

Multiple Choice

Most car batteries contain:

• citric acid

• sulfuric acid

• tartaric acid

• lactic acid

Multiple Choice

All acids provide --- ions

• hydrogen

• hydroxide

• chloride

• sulfate

Multiple Choice

Sting of a bee injects you with:

• sulfuric acid

• formic acid

• lactic acid

• tartaric acid

Fill in the Blanks

Acids react with certain metals to form _ gas

Open Ended

State the difference between a dilute acid and a concentrated acid.

Open Ended

Write down the important difference between organic acids and mineral acids.