“We must trust to nothing but facts: These are presented to us by Nature, and cannot deceive. We ought, in every instance, to submit our reasoning to the test of experiment, and never to search for truth but by the natural road of experiment and observation.” ― Antoine Lavoisier, Elements of Chemistry

Thursday, 13 November 2014

Review: Acids and Bases for Checkpoint

¢  An acid is a compound/substance that produces hydrogen ions (H+) when dissolved in water
¢  Acids taste sour.
¢  Acids turn indicators red
¢  An acid has pH lower than 7

¢  Bases are ionic compounds that produce hydroxide ions (OH-) when dissolved in water .
¢  Bases taste bitter and feel slippery
¢  Bases turn indicators blue
¢  Bases release hydroxide ions in water solutions (the more released, the stronger the base)
¢  Has pH more than 7; pH range  7-14

¢  Indicators are weak organic acids or bases which have the property of changing color in solution when the hydrogen ion concentration reaches a definite value.
¢  The most used indicator is litmus (extracted from lichens)
¢  Blue paper litmus changes color to red in acid solution
¢  Red paper litmus turns blue in alkali solution
Acids Affect Indicators, by changing their color

Blue litmus paper turns  red  in contact with an acid  (and red paper stays red).

Bases Affect Indicators

Red litmus paper turns  blue  in contact with a base (and blue paper stays blue).
Phenolphthalein turns purple in a base.
The pH scale
¢  The pH scale is a measure of the hydrogen ion concentration, the scale runs from 0 to 14
¢  Acids have pH less than 7, more strength acid, the lower the pH
¢  Neutral substances have a pH of 7
¢  Bases have pH 7 to 14, more alkaline in solution, the higher the pH
¢  The pH of a solution can be measured by universal indicator paper and pH meter

More on pH
¢  If you add an acid to water, the concentration of hydrogen ions increases and the concentration of hydroxide decreases. 
¢  The lower the pH value, the greater the hydrogen ion concentration.
¢  If you add base to water the concentration of hydroxide increases and the hydrogen ion concentration decreases.

¢  The higher the pH value, the lower the hydrogen ion concentration.

Common Acids and Bases

¢  Hydrochloric acid   HCl
¢  Nitric acid                            HNO3
¢  Sulphuric acid                    H2SO4
¢  Sodium hydroxide   NaOH
¢  Calcium hydroxide Ca(OH)2
¢  Magnesium hydroxide   Mg(OH)2
¢  Ammonium hydroxide  NH4OH


1.       Name 2 acids and their uses.

 2.       Name 2 bases and their uses.

 3.       Describe one way you can safely determine whether an unknown solution is an acid or base?

4.     How can an acid be neutralized?

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