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Properties and Classification of Acids and Bases Tutorial

Key Concepts

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Properties of Acids and Bases

Many substances can be classified as acids or bases on the basis of their properties.

Acids and bases are not just found in the laboratory, they also found in and around your home.
Citrus fruits like oranges, lemons and grapefruit, taste sour because they contain acids.
Baking soda, on the other hand, tastes quite bitter, because it contains a base.

One of the properties of acids is that they taste sour.
One of the properties of bases is that they taste bitter.

Ofcourse you should NEVER taste anything in the laboratory, but this difference in taste is just one example of how the properties of acids and bases differ.
In general, the properties of acids and bases are different, with the exception that solutions of acids and solutions of bases both conduct electricty.

Properties of Acids Properties of Bases

  • solutions conduct electricity
  • bitter taste
  • slippery or soapy feel1
  • change red litmus to blue
  • neutralise acids

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Classification and Uses of Acids and Bases

Acids and bases can be further classified based on the presence or absence of carbon atoms:

Carbonic acid, H2CO3, is an exception to this classification. Carbonic acid contains carbon, BUT it is classified as an inorganic acid rather than as an organic acid.

Inorganic (Mineral) Acids: Inorganic Alkalis
(water soluble bases):
(i) hydrochloric acid, HCl

  • Use to clean metals and mortar.
  • Used in swimming pools to adjust pH.
  • Found in the stomach for digestion of food.

(ii) sulfuric acid, H2SO4

(iii) nitric acid, HNO3

  • Used in the manufacture of fertilizers.
  • Used to make explosives (TNT and dynamite).

(iv) phosphoric acid, H3PO4

  • Used as a food acid.
  • Used in anti-rust products for cars.

(v) carbonic acid, H2CO3

  • Formed when carbon dioxide gas, CO2, dissolves in water.

(i) sodium hydroxide, NaOH

  • Other names: caustic soda.
  • Used to clean blocked drains.
  • Used to make soaps and detergents.

(ii) potassium hydroxide, KOH

(iii) aqueous ammonia, NH3(aq)

  • Used in some cleaning products
    (cloudy ammounia, floor cleaners)

Organic Acids: Organic Alkalis
(water soluble bases):
Carboxylic acids are organic acids.

Examples include:

(i) formic acid (methanoic acid), HCOOH

  • Found in ant stings.

(ii) acetic acid (ethanoic acid), CH3COOH

  • Found in vinegar.

(iii) butanoic acid (butyric acid), C3H7COOH

  • Gives rancid butter its characteristic smell

(iv) citric acid (2-hyroxypropane-1,2,3-tricarboxylic acid), C6H8O7

  • Found in citrus fruits such as oranges and lemons.
  • Used an antioxidant in canned foods.

Amines are organic bases.

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Sample Questions with Worked Solutions

Question 1: A reagent bottle, labelled Reagent A, contains a white powder.
When dissolved in water the resulting aqueous solution conducts electricity.
When red litmus paper is placed in the solution it remains red.
When blue litmus paper is placed in the solution it changes colour from blue to red.
Is Reagent A an acid or a base?

  1. List the relevant properties of acids and bases:
    Property Acid Base
    electrical conductivity conducts conducts
    red litmus no change changes to blue
    blue litmus changes to red no change
  2. Tick off the properties displayed by Reagent A:
    Property Acid Base
    electrical conductivity conducts conducts
    red litmus no change changes to blue
    blue litmus changes to red no change
  3. Decide whether Reagent A is an acid or a base:
    Reagent A is an acid because to turns blue litmus red, but does not change the colour of red litmus.

Question 2: Bo the Biologist has noticed a white material coating the inside of the kettle in the Biology kitchen.
"It's just lime-scale, calcium carbonate that gets deposited inside the kettle," explains Chris the Chemist. "But I have the solution," Chris chuckles while reaching into the kitchen cupboard to extract a bottle to give to Bo.
Do you think Chris the Chemist handed Bo a bottle of oven cleaner or a bottle of vinegar?

  1. List the relevant properties of acids and bases, that is, the reaction between acids or bases and calcium carbonate:
    Property Acid Base
    reaction with carbonates produces carbon dioxide gas no visible reaction
  2. Identify the type of reagents Chris could have given Bo:
    Acid Base
    vinegar oven cleaner
  3. Decide which reagent could be used to clean off the lime-scale (calcium carbonate)
    Property Acid
    (vinegar)
    Base
    (oven cleaner)
    reaction with carbonates produces carbon dioxide gas no visible reaction

    Vinegar could be used to clean off the lime-scale because it is an acid and acids react with carbonates to produce carbon dioxide gas.

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1. Alkali (water soluble base) can react with the fat from your skin in a saponification reaction (literally a soap-making chemical reaction) so your fingers get that slippery, soapy feel!