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Chemistry
for Secondary Schools

FOR ONLINE READING ONLY

Citrus fruits Pineapples Plums Passion fruits

Figure 5.1: Some fruits with natural sources of acids

Table 5.1: Examples of natural acids and their sources
Name of natural acid Natural sources

Citric acid Citrus fruits such as lemons and oranges
Lactic acid Sour milk, cheese, and other fermented dairy products

Acetic acid Vinegar and rotten fruits such as grapes, pineapple
and oranges

Tartaric acid Grapes, bananas and tamarind
Oxalic acid Spinach and tomatoes

Formic acid Bee or ant stings
Ascorbic acid Fruits and vegetables, for example, tomatoes,
pawpaws, broccoli, oranges and grape fruits
Folic acid Fruits, vegetables, nuts and grains

Malic acid Apples, strawberries and plums

On the other hand, synthetic acids are artificially produced acids. Examples of
synthetic acids include sulfuric acid, nitric acid and hydrochloric acid.

Acids can be classified as mineral (inorganic) acids and organic acids. Mineral

acids are synthesised in industries from inorganic substances, while organic
acids are synthesised in industries or obtained directly from natural organic
materials. Examples of mineral acids include nitric acid (HNO 3 ), sulfuric
acid (H 2 SO 4 ), hydrochloric acid (HCl), carbonic acid (H 2 CO 3 ), phosphoric
acid (H 3 PO 4 ), nitrous acid (HNO 2 ), and sulfurous acid (H 2 SO 3 ). Examples of
organic acids include ethanoic acid/acetic acid (CH 3 COOH) and methanoic

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