Acids Bases and Salts – Important Questions & Chapter Revision

Let’s discuss each topic one-by-one

• What are acids and bases – All acids give H+ ions in solution, and all bases give OH- ions

However, some acids dissociate to give more H+ ions, and are said to be a strong acids. Similarly, a base producing more OH- ions is a strong base.

• Detecting an acid or a base – We use litmus solution, phenolphthalein or methyl orange for this purpose. The colour change that they show in acidic and basic solutions are:

We can also measure strength of an acid or a base using a pH scale, which looks something like this:

Strong acids have pH value lying around 0, while strong bases have pH lying around 14. This means, more the number of H+ions in solution, lesser will be its pH. Below are the names and formulae of some common acids and bases. You can also see the number of H+ and OH- ions released by one molecule of each of them

Common reactions of acids and bases: Reactions of acids and bases have been dealt with in this chapter, and for all these reaction types, you should remember the product formed.

• Acid + metal → salt + H2 gas
• Acid + metal carbonate/bicarbonate → salt+water+carbon dioxide
• Acid + base (i.e. metal hydroxide) → salt + water
• Acid + Metal oxide → Salt + Water
• Non-metal oxide + Base → Salt + Water

From last two reactions, we can say that metal oxides are basic in nature. Similarly, non-metallic oxides are acidic in nature.
You can create a chemical equation from these equations, by inserting correct formula of acid/base and metal with correct valency.

For example, Zn+H2SO4—>ZnSO4+H2

Do not forget to balance the equation!

Importance of pH in everyday life – This is also an important topic from exam point of view, and a very easy one too. So make sure you study this topic thoroughly

• Our body works within the pH range of 7.0 to 7.8.
  Interestingly, living organisms usually get affected by small pH changes.
• pH in our digestive system – Our stomach produces HCl, which helps in digestion of food. But sometimes, if the amount of HClincreases, we suffer from acidity. The antacids given to us for getting relief from acidity contain base in them i.e. Magnesium Hydroxide.
• pH of our mouth – if the pH of our mouth gets lower than 5.5, tooth decay starts. To avoid this, we should clean our teeth properly after meals.
• pH in animal bites – many bees and insects inject an acid when they sting. The medicines or lotions available for their relief also contain a mild base in them.
• Acid rain – If the pHof rain is lower than 5.6 we term it ‘acid rain’. This water, when flows in water bodies, makes the water acidic and difficult for aquatic organisms to survive. It also causes a harm to monuments like Taj Mahal.

Salts, and chemicals made from common salt – we know that a salt is formed from the combination of an acid and a base. Many other salts are made from common salt, which have many uses in daily life.  

Note that there is a high probability of a question appearing in boards from this topic, so make sure you study  this topic thoroughly.
One important compound which is manufactured using NaCl is NaOH. 
Below are few names, formulae, preparation and uses of some more compounds manufactured using NaCl, or from products obtained from NaCl.

Water of crystallization – Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt.

Most salt molecules are coloured when moist, but become colourless when heated.

For example, hydrated copper sulphate CuSO4.5H2O is blue in colour, and becomes white in colour when heated:

CuSO4.5H2O—->CuSO4+5H2O

Let us now understand weightage of this chapter.

Looking at previous years’ questions, we can say that there is a higher probability of a 1 or a 2 mark question appearing from this chapter.
.1 mark:

• How does the flow of acid rain water into a river make the survival of aquatic life in the river difficult? [CBSE, 2008]
• What effect does an increase in concentration of H+(aq) in a solution have on the pH of solution? [CBSE, 2009]

2 marks:

• Write the chemical formula for washing soda. How may it be obtained from baking soda? Name an industrial use of washing soda other than washing clothes. [CBSE, 2008]
• I.  Name the products formed when sodium hydrogen carbonate is heated.

II.Write the chemical equation for the reaction involved in the above process. [CBSE, 2009]

Let’s solve one of the questions: