Free download NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts in PDF form. All NCERT solutions are available in PDF form to download or view online. Solutions are based on latest CBSE Curriculum for 2017 – 18.
NCERT Solutions for Class 10 Science Chapter 2
Important Questions for Board Exams – 2018
Class 10 Chemistry – Acids, Bases and Salts
Define indicators. Name two natural indicators obtained from plants.
Indicators are substances which give different colour in acid or bases solutions. Natural indicators from plants are: (a) Litmus, (b) Vanilla extract.
What are antacids?
Antacids are mild alkalies. These are used for getting relief from acidity and indigestion and sometimes, even headache. When taken orally, it reacts with hydrochloric acid present in the stomach and reduces its strength by consuming some of it. For example, milk of magnesia is an antacid.
What are olfactory indicators? Give an example.
Olfactory indicators are substances which have different odour in acid and base solutions. For example, vanilla essence has characteristics pleasant smell in acid solution and no smell in alkali solution.
What is a neutralization reaction? Give some examples.
When the effect of a base is nullified by an acid and vice versa, it is called neutralization reaction. In general, a neutralization reaction is written as:
Base + Acid ―> Salt + Water
(a) Aqueous solution of base, NaOH is neutralized by aqueous hydrochloric acid. (b) Aqueous solution of sulphuric acid is neutralized by aqueous solution of sodium hydroxide. Question 5:
Tap water conducts electricity whereas distilled water does not. Why?
Tap water contains some impurities in the forms of salts. Due to presence of salts, it conducts electricity. Distilled water is free from all kinds of salts and hence does not conduct electricity.
While diluting an acid, why is it recommended that the acid should be added to water and not water into the acid?
When an acid is mixed with water, there is evolution of large amount of heat. Therefore, acid is slowly added to water. If on the other hand, water is added to acid, it might spill on your body and clothes due to explosion and evolution of sudden and large amount of heat.
What is meant by the term pH of a solution? The pH of rain water collected from two cities A and B was found to be 6 and 5 respectively. The water of which city is more acidic?
pH is a term which indicates whether a solution is acidic of basic and to what extent. Mathematically it is a measure of H^+ ions concentration in water.
The rain water collected from city B is more acidic.
Tooth enamel is one of the hardest substance in our body. How does it undergo damage due to eating chocolates and sweets? What should we do to prevent it?
Sugar present in chocolates and sweets gets broken to acids by bacteria present in the mouth. This lowers the pH in the mouth. Tooth enamel is made up of calcium phosphate, which gets corroded when the pH in the mouth is below 5.5. To prevent tooth enamel from decay, toothpaste is used because it is alkaline and neutralises the acid produced in the mouth and helps to prevent lowering of pH in mouth.
(a) How is common salt prepared from sea water?
(b) What will be the approximate pH of the aqueous solutions of the following salts:
(i) Sodium Chloride (ii) Ammonium Chloride
(a) Sodium chloride is a white solid. It is obtained on a large scale by evaporation of sea water. The crude salt so obtained contains impurities such as sodium sulphate, calcium sulphate, calcium chloride and magnesium chloride. The crude salt is dissolved in water, the impurities are filtered off and the pure sodium chloride is precipitated out from the solution by passing chlorine gas.
(b) (i) Sodium chloride solution : nearly pH 7
(ii) Ammonium chloride : pH = 2 -4
An alkali is an important base used for the laboratory work. Name the base and sate hoe it can be prepared from common salt? What is this process called?
An important alkali commonly needed for laboratory work is sodium hydroxide. It can be prepared from sodium chloride by the process of electrolysis. This is called chlor-alkali process.
Electrolysis of aqueous solution of sodium chloride: When electricity is passed through an aqueous solution of sodium chloride commonly called brine, it decomposes into chloride and sodium. Sodium is collected at the cathode where it reacts with water to form sodium hydroxide. Chlorine is formed at the anode and is collected as a gas. At Cathode: At Anode: The overall reaction is Question 11:
(a) How does baking soda helps to make cakes and bread soft and spongy? OR
Give reason: cake rise on adding baking powder.
(b) Write chemical equation for its preparation.
(a) On heating , sodium bicarbonate decomposes to produce carbon dioxide. This causes biscuits and cakes etc. to expand and become light. The other constituents act as preservatives. (b) Question 12:
Why does bleaching powder smell strongly of chlorine?
Bleaching powder smells strongly of chlorine because it slowly reacts with carbon dioxide of air to evolve chlorine gas. Question 13:
Why are commercial samples of bleaching powder not completely soluble in water?
Bleaching powder is soluble in water. However, commercial samples of bleaching powder contains slaked lime that does not react with chlorine gas during the manufacture of bleaching powder. The insoluble part of bleaching powder is this white solid, i.e., slaked lime.