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By: Ikedi Ani-okoye.

Acids and Alkalis

Lemon juice and vinegar taste sour Because they contain weak acids. An acid is a substance that dissolves in water to form positively charged particles called hydrogen ions (H+). The opposite of an acid is an alkali, which dissolves in water to form negatively charged ions of hydrogen and oxygen) called hydroxide ions (OH-). Alkalis are "anti- acids" because they cancel out acidity. Toothpaste, for exampled contains an alkali to cancel out acidity In the mouth that would otherwise damage teeth.

PH scale

The concentration of hydrogen ions in a solution is known as its pH. Scientists use the pH scale to measure acidity and alkalinity. On the pH scale, a solution with a pH lower than 7 is acidic, and a solution with a pH greater than 7 is alkaline. Water is neutral, with a pH of 7. A solution's pH can be tested with universal indicator solution or paper, which changes colour in acids and alkalis.

Strong acids

The more hydrogen ions an acid forms in water, the stronger it is, and the lower its pH. Strong acids, such as sulphuric acid and nitric acid, are very dangerous and must be handled carefully.

Acids and metals

Even the weakest acids cannot be stored in metal containers because acids are corrosive to most metals. When an acid reacts with a metal, hydrogen gas is given off and the metal dissolves in the acid to form a compound called a salt. The reaction is very violent with metals such as potassium and sodium, and quite vigorous with metals such as magnesium and zinc.

Bases and alkalis

The acidity of vinegar (ethanoic acid) can be neutralized, or cancelled out, by adding chalk (calcium carbonate). Any substance that neutralizes acidity, such as chalk, is called a base. An alkali is a base that dissolves in water. An alkali's strength is measured by the number of hydroxide ions it forms in water. Strong alkalis, such as sodium hydroxide, are just as corrosive as strong acids.

Soaps and detergents

Alkalis are good at dissolving oil and grease, so they are widely used in the manufacture of soaps an& detergents. Most dirt is bound to skin, clothes, or eating utensils by grease. The grease makes it difficult to remove dirt with water alone, because water and grease do not mix. A soap or detergent, such as washing-up liquid, breaks the grease up into tiny drops and allows the water to wash away the dirt.

Neutralizing acids

Alkali and an acid react together to give a aeutral salt. In addition, hydroxide ions (OH-) the alkali combine with the acid's hydrogen ions (H+) to Produce water (H20). In daily life, problems of unwanted acidity are solved by adding an alkali of the appropriate strength.

Alkali industry

The main raw material in the alkali industry is brine (salt water). Sodium hydroxide, which is used to make soaps and paper, is produced from brine by electrolysis (passing electricity through it). Brine will also absorb carbon dioxide to make sodium carbonate, which is used in textile treatment, photography, and glass making.

Acid industry

Acids are widely used in industry because they react so readily with other materials. For example, sulphuric acid is used in the production of dyes and pigments, artificial fibres, plastics, soaps, and explosives. The acid is made by sulphur oxygen reacting together.