The study of acids and bases is an essential part of Chemistry Topics, as it examines their properties and reactions.
What are Strong Bases and Weak Bases ? And What are Neutral Substances ?
If we take some baking soda and taste it, the baking soda appears to have a bitter taste (kadwa taste). And if we rub a solution of baking soda between our fingers, it feels soapy to touch (or slippery to touch). The substances (such as baking soda) which are bitter in taste and feel soapy to touch are known as bases.
Bases are the chemical opposites of acids. When bases are added to acids, they neutralise (or cancel) the effect of acids. We can now define bases as follows :
A substance which can neutralise an acid to form a salt (and water) is called a base. Bases have bitter taste. Bases turn red litmus to blue. Some of the examples of bases are :
- Sodium hydroxide
- Potassium hydroxide
- Calcium hydroxide
- Magnesium hydroxide
- Ammonium hydroxide (Ammonia solution)
- Sodium carbonate
- Sodium hydrogencarbonate
A base which is soluble in water is called an alkali. All the bases which we have given above are soluble in water so all of them are alkalis (see Figure).
- Sodium hydroxide and potassium hydroxide are found in soap.
- Calcium hydroxide is found in lime water.
- Magnesium hydroxide is found in milk of magnesia.
- Ammonium hydroxide (also called ammonia solution) is found in window cleaners.
- Sodium carbonate is found in washing soda.
- Sodium hydrogencarbonate is found in baking soda.
Strong Bases and Weak Bases
Like acids, bases can also be strong or weak. Some of the strong bases and weak bases are given below :
As we can see above, sodium hydroxide and potassium hydroxide are strong bases. Sodium hydroxide is commonly known as ‘caustic soda and potassium hydroxide is commonly known as ‘caustic potash’ (‘caustic’ means ‘corrosive’ or ‘burning’).
Sodium hydroxide and potassium hydroxide are dangerous bases which can burn our skin. They must be handled very carefully. Calcium hydroxide, ammonium hydroxide and sodium carbonate are weak bases but their solutions are unsafe to drink.
Magnesium hydroxide is, however, a very weak base which is safe to drink. It is used in milk of magnesia and other indigestion mixtures. Similarly, sodium hydrogencarbonate is a very weak base which is used as an antacid to cure indigestion.
We know that some of the sugary food eaten by us is converted into acid by the bacteria present in our mouth. And this acid causes tooth decay. The toothpaste which we use for brushing and cleaning our teeth is basic in nature. Since toothpaste is basic, it neutralises the acid in our mouth and hence prevents tooth decay. We will now give the main points of difference between acids and bases.
Main Differences Between Acids and Bases
|1.||Acids have sour taste.||1.||Bases have bitter taste.|
|2.||Acids are not soapy to touch.||2.||Bases feel soapy to touch.|
|3.||Acids turn blue litmus to red.||3.||Bases turn red litmus to blue.|
Great care should be taken in handling laboratory acids and bases because they are corrosive in nature, irritating and harmful to skin.
Those substances which are neither acidic nor basic in nature are called neutral substances. Being neither acidic nor basic, neutral substances do not change the colour of any indicator.
Thus, if the solution of a substance in water does not change the colour of either blue litmus or red litmus, then it will be a neutral substance. Some of the neutral substances are : Pure water (or Distilled water), Glucose, Canesugar and Common salt.
We can confirm the neutral nature of substances by performing the litmus test. For example, let us put one drop of distilled water on blue litmus paper and another drop of distilled water on red litmus paper. We will find that there is no change in the colour of blue litmus paper or red litmus paper.
This shows that distilled water is neither acidic nor basic in nature. So, distilled water is neutral. We can show the neutral nature of glucose, canesugar and common salt in a similar way by testing their water solutions (aqueous solutions) with blue litmus paper and red litmus paper, turn by turn.
We will now answer some questions based on acids and bases.
Example Problem 1.
You have been provided with three test-tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test-tube ?
- Put the red litmus paper in all the test-tubes, turn by turn. The solution which turns red litmus to blue will be a basic solution. The blue litmus paper formed here can now be used to test the acidic solution.
- Put the blue litmus paper (obtained above) in the remaining two test-tubes, one by one. The solution which turns the blue litmus paper to red will be the acidic solution.
- The solution which has no effect on any litmus paper will be neutral and hence it will be distilled water.
Example Problem 2.
Three liquids are given to you. One is hydrochloric acid, another is sodium hydroxide and the third is a sugar solution. How will you identify them ? You have only turmeric paper indicator.
- Put one drop of each liquid on turmeric paper, turn by turn. The liquid which turns the yellow turmeric paper red will be sodium hydroxide (base). The red turmeric paper formed here can now be used to test hydrochloric acid.
- Put one drop each of the remaining two liquids on red turmeric paper. The liquid which makes the red turmeric paper yellow again will be hydrochloric acid (This is because hydrochloric acid cancels the effect of sodium hydroxide base on turmeric paper).
- The liquid which has no effect on the red turned turmeric paper will be sugar solution (because it is neutral).
Note. Though we have not studied elements and compounds so far but we should remember the following elements and their symbols as well as the following compounds and their formulae because they will be used in the discussion of our next topics on neutralisation and ‘salts’.
|Hydrochloric acid||HCl||Ammonium chloride||NH4Cl|
|Sulphuric acid||H2SO4||Sodium sulphate||Na2SO4|
|Nitric acid||HNO3||Ammonium sulphate||(NH4)2SO4|
|Carbonic acid||H2CO3||Potassium nitrate||KNO3|
|Sodium hydroxide||NaOH||Sodium carbonate||Na2CO3|
|Potassium hydroxide||KOH||Sodium hydrogencarbonate||NaHCO3|