Page 21 - Curriculum Visions Dynamic Book

 Litmus is cherry red in an acidic solution and purple–blue in an alkaline solution.
 Bromothymol blue is yellow in an acidic solution but blue in an alkaline solution.
acidity: a general term for the strength of an acid in a solution.
indicator: a substance or mixture
of substances that change colour with acidity or alkalinity. Indicators measure the pH of a solution.
ion: an atom, or group of atoms, that has gained or lost one or more electrons and so developed an electrical charge.
pH: a measure of the hydrogen ion concentration in a liquid. Neutral is pH 7.0; numbers greater than this are alkaline, smaller numbers are acidic.
 Phenolphthalein is colourless in an acid solution, but turns purple in an alkaline solution.
 Methyl orange is red in an acidic solution but yellow in an alkaline solution.
The importance of acid testing
Many chemical processes, the manufacture of food, and successful farming all rely on a careful control of pH.
Environmental scientists measure the pH of falling rainwater. If the pH reading is less than five, then the rain is classed as acid rain. Acid rain is one of the most serious environmental problems of our time.
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