NCERT Solutions prepared by experts having good knowledge about science. The solutions also include diagrams and relevant formulas to help students in visualizing and understand better.
CBSE NCERT Solutions for Class 7 Science Chapter 5:
Name the source from which litmus Solution is obtained. What is the use of this
Litmus Solution is obtained from lichens dissolved in distilled water. It is used to
detect the acidic and basic characteristic of a substance as it changes its colour to red in acidic medium and into blue in basic medium.
Is the distilled water acidic/basic/neutral? How would you verify it?
The distilled water is neutral. Litmus paper can be used to verify whether the
distilled water acidic/basic/neutral. Distilled water doesn't changes the colour of blue or red litmus paper. So, it is neutral in nature
Describe the process of neutralisation with the help of an example.
When an acid Solution and a base Solution are mixed in suitable amounts
both the Solutions neutralise the effect of each other and a new substance salt is
formed. This process is called neutralisation. When the Solution of sodium
hydroxide (a base) and hydrochloric acid (an acid) is mixed in test tube in proper
ratio, both neutralize each other. In this reaction, a new substance sodium chloride isformed. The mixture obtain is neutral in nature which can be justified by litmus
Solution or phenolphthalein Solution.
The reaction can be written as:
Hydrochloric acid (HCl) + Sodium hydroxide(NaOH) → Sodium Chloride(NaCl) +
Water (H 2 O)
Dorji has a few bottles of soft drink in his restaurant. But, unfortunately, these
are not labelled. He has to serve the drinks on the demand of customers. One customer wants acidic drink, another wants basic and third one wants neutral drink. How will Dorji decide which drink is to be served to whom?
Dorji will take red and blue litmus paper and dip it into every bottles of soft drink. The drink in which red litmus paper turns blue is bottle of basic drink. The drink in which blue litmus paper turns red is bottle of acidic drink. The drink in which both litmus paper show no changes in colour is of neutral drink.
Three liquids are given to you. One is hydrochloric acid; another is sodium
hydroxide and third is a sugar Solution. How will you identify them? You have only turmeric indicator.
Dip the turmeric indicator in each liquid. The liquid in which the colour of
turmeric indicator changes to red is basic in nature i.e. sodium hydroxide. Since, we already identified sodium hydroxide. We will pour the sodium hydroxide in other two bottles. The liquid which get warm after pouring the sodium hydroxide (base) in it is of hydrochloric acid as heat gets evolved in the neutralisation process. The last one which shows no effect is liquid of sugar Solution.