Page 31 - Curriculum Visions Dynamic Book

 Vinegar reacting with bicarbonate of soda.
dissociate: to break apart. In the case of acids it means to break up forming hydrogen ions. This is an example
of ionisation. Strong acids dissociate completely. Weak acids are not completely ionised and a solution
of a weak acid has a relatively low concentration of hydrogen ions.
electrolyte: a solution that conducts electricity.
weak acid: an acid that has only partly dissociated (ionised) in water. Most organic acids are weak acids.
 This is a representation of acetic acid, which is found in vinegar.
The hydrogen atoms marked with
the “❊” symbol will dissociate from the molecule when in water. This is what makes this compound a weak acid.
 Citrus fruits contain citric acid, a weak acid, which gives these fruits their
sour taste.
Acetic acid
Acetic acid is a colourless, weak, corrosive organic acid. Its formula is CH3COOH. It provides the taste in vinegar.
Vinegar was first made by fermenting fruit beyond the stage needed for making wine. Wine always contains acetic acid; over-fermented wine has a distinct acid taste. Vinegar has a concentration of about 5% acetic acid.
Acetic acid reacts with various alcohols to make the range of solvents called acetates. It is also a raw material of the artificial fibre, rayon. Acetylsalicylic acid is better known as the painkiller aspirin.
Industrial acetic acid is made from carbon monoxide and hydrogen.
The first step is to form methyl alcohol from hydrogen and carbon monoxide. Adding excess carbon monoxide creates acetic acid.
Citric acid
Citric acid is a
solid, white, organic
acid. It is found in all animal
and plant cells where it is used as
part of the process of metabolism. It is especially rich in citrus fruits, especially lemons and limes. It is more acidic (i.e. it has a greater concentration of H+ ions in solution) than acetic acid.
The formula for citric acid is HOC(CH2OOH)2COOH. Citric acid can be made by decomposing molasses from sugar beet using mould. The acid occurs as part of natural fermentation.
Citric acid is used industrially as a preservative in food, as a cleaning and polishing agent for metal and in soft drinks and flavourings.
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