Chemistry » Acid-Base and Redox Reactions » Acids And Bases Continued

# Further Defining Acids and Bases

## Again! What are acids and bases?

We encounter many examples of acids and bases in our daily lives. Some common examples of household items that contain acids are vinegar (contains acetic acid), lemon juice (contains citric and ascorbic acid), wine (contains tartaric acid). These acids are often found to have a sour taste. Hydrochloric acid, sulfuric acid and nitric acid are examples of acids that are more likely to be found in laboratories and industry.

Some common household acids.

Hydrochloric acid is also found in the gastric juices in the stomach. Fizzy drinks contain carbonic acid, while tea and wine contain tannic acid. People even use acids in an artistic process known as acid etching. In acid etching, a metal is covered in a waxy material that is resistant to acid. The bare metal is then exposed in the desired pattern and the sample is placed in an acid bath. The top layers of the exposed metal are permanently removed, creating the desired image. Some examples of this are shown below (see the figure below).

Some examples of the acid etching of metal.

Bases that you may know about include sodium hydroxide (commonly known as caustic soda), ammonium hydroxide and ammonia. Some of these are found in household cleaning products. Bases are usually found to have a bitter taste and feel slippery (soap is a good example). Acids and bases are also important commercial components in the fertiliser, plastics, and petroleum refining industries. Some common acids and bases, and their chemical formulae, are shown in the table below.

 Acid Formula Base Formula Hydrochloric acid $$\text{HCl}$$ Sodium hydroxide $$\text{NaOH}$$ Sulfuric acid $$\text{H}_{2}\text{SO}_{4}$$ Potassium hydroxide $$\text{KOH}$$ Nitric acid $$\text{HNO}_{3}$$ Magnesium hydroxide $$\text{Mg}(\text{OH})_{2}$$ Oxalic acid $$\text{H}_{2}\text{C}_{2}\text{O}_{4}$$ Calcium hydroxide $$\text{Ca}(\text{OH})_{2}$$ Sulfurous acid $$\text{H}_{2}\text{SO}_{3}$$ Sodium bicarbonate $$\text{NaHCO}_{3}$$ Phosphoric acid $$\text{H}_{3}\text{PO}_{4}$$ Sodium carbonate $$\text{Na}_{2}\text{CO}_{3}$$ Acetic (ethanoic) acid $$\text{CH}_{3}\text{COOH}$$ Ammonium hydroxide $$\text{NH}_{4}\text{OH}$$ Carbonic acid $$\text{H}_{2}\text{CO}_{3}$$ Ammonia $$\text{NH}_{3}$$

Table: Some common acids and bases and their chemical formulae.

#### Tip:

Dissociation is the breaking apart of a molecule to form smaller molecules or ions, usually in a reversible manner.

#### Fact:

The wild lupin plant takes nitrogen from the atmosphere and creates ammonia. It uses that ammonia to fertilise the soil for itself and the surrounding plants.

#### Fact:

Sodium bicarbonate is used in baking. It reacts with the acids in dough to release carbon dioxide. The carbon dioxide then causes the dough to expand.

## Optional Activity: Naturally occurring acids and bases

Do research on three naturally occurring acids, and one naturally occurring base. That is, acids and bases that are found mostly in plants (not man-made).

• Where the acid or base is found (e.g. the plant in which it occurs).

• Indigenous uses of the plant.

• What the chemical composition of the acid or base is.

The next section deals with some models used to describe acids and bases. It is important to have a definition so that acids and bases can be correctly identified in reactions.