Acids and acid rock drainage

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page 2 Ways of testing acidity The roots of the Noni tree can be used as an indicator of acidity or pH, because they turn yellow when exposed to acids and red when exposed to bases. There are ways of testing or checking to see whether something is acidic. You can use paper that is soaked in a special chemical (litmus paper) or you can use some plants, for example the roots of the Wol or Noni (Morinda citrifolia) plant. If the substance you are testing is acidic, the colour of the litmus paper or Noni roots will change. ˆ Acids turn litmus paper red and the roots of the Noni tree yellow ˆ Bases turn litmus paper blue and the roots of the Noni tree red. Some acids are stronger than others. The strength of the acid can be measured on the pH scale. > > The chemistry of acids and bases Acids and bases are only acidic and basic when they are dissolved in water. The chemical equations opposite show how this happens. Hydrochloric acid (HCl) dissolves in water as follows: HCl + H 2 O Y H + (aq) + Cl - (aq) A typical base, sodium hydroxide (NaOH) dissolves in water as follows: NaOH + H 2 O Y Na + (aq) + OH - (aq)
page 3 The pH scale and pH values Kambang (lime) from Londolovit market is strongly basic. It makes the red colour when chewing betel nut. The pH scale is a means of measuring how acidic and basic different substances are. The pH scale goes from 0 to 14. The middle of this scale is 7, which is neutral, so anything with a pH value of 7 is neither acidic nor basic. Distilled water which has a pH of 7 is neutral. Substances that have a pH less than 7 are acidic. Stronger acids have a small pH value, for example, stomach acid has a pH of 1, and lemons, a common source of citric acid, have a pH of just above 2. All bases (also called alkalis) have a pH of more than 7. Stronger bases have a larger pH, for example kambang has pH of 12. Bleach has a pH of over 12, is highly basic, and just as corrosive as strong acids. Thus the strongest acids are closest to 0 on the scale, and the strongest bases are closest to 14. Values of the pH scale Each number on the pH scale, from 1 to 14, represents a change of ten times from the previous number. A highly acidic substance with a pH of 1, such as stomach acid, is ten times more acidic than lemon juice which has a pH of 2, and 100 times more acidic than something with a pH of 3, like vinegar. strong weak weak strong acid neutral base Similarly, a strong basic such as bleach, with a pH of 12, is ten times more basic than laundry detergent, which has a pH of 11.
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Acids and acid rock drainage

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