Class 10 Science Acid base and Salts Long Questions( Five Marks questions)
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Question 1
(a) List in tabular form two differences between an acid and a base based on their chemical properties.
(b) State the meaning of neutralization reaction. Give two examples to illustrate your answer.
Question 2
A student dropped few pieces of marbles in dilute hydrochloric acid, contained in a test tube. The evolved gas was then passed through lime water. What change would be observed in lime water? What will happen if excess of gas is passed through lime water? Write balanced chemical equations for all the changes observed. Solution
Marble is nothing but calcium carbonate
CaCO3 + HCl -> CaCl2 + H20 + CO2
When CO2 is passed through lime water,The first reaction produces CaCO3 which is insoluble in water and hence the solution turns milky.
Ca(OH)2 [lime water] + CO2 -- CaCO3 + H2O
If furthermore CO2 is passed,the CaCO3 reacts with the CO2 to form Ca(HCO3)2 which is soluble in water and hence the solution becomes colourless.
CaCO3 + CO2 + H2O -- Ca(HCO3)2
Question 3
What is observed when carbon dioxide gas is passed through lime water.
(a) for a short duration?
(b) for long duration?
Also write the chemical equations for the reactions involved. Solution
When CO2 is passed through lime water,The first reaction produces CaCO3 which is insoluble in water and hence the solution turns milky.
Ca(OH)2 [lime water] + CO2 -- CaCO3 + H2O
If furthermore CO2 is passed,the CaCO3 reacts with the CO2 to form Ca(HCO3)2 which is soluble in water and hence the solution becomes colourless.
CaCO3 + CO2 + H2O -- Ca(HCO3)2
Question 4
State reasons for the following statements:
(a) Tap water conducts electricity, whereas distilled water does not.
(b) Dry hydrogen chloride gas does not turn blue litmus red, whereas hydrochloric acid does.
(c) During summer season, a milkman usually adds a very small amount of baking soda to fresh milk.
(d) For dilution of an acid, acid is added into water and not water into acid.
(e) Ammonia is a base but does not contain a hydroxyl group. Solution
(a) Tap water contains ions which conduct electricity, distilled water does not contain ions.
(b)Dry HCl does not form ions but HCl gives H+ and Cl–.
(c) Baking soda does not allow milk to change to lactic acid which makes milk sour.
(d) Adding water to acid is highly exothermic. Therefore water is added to acid very slowly with cooling.
(e)Ammonia when dissolved in water it forms ammonium hydroxide.
Ammonium hydroxide readily ionizes to form ammonium ions (NH4+) and hydroxide ions
(OH-). Thus the solution ammonia is considered as a base
Question 5
(a) In a tabular form write the colours of the following indicators in presence of acid and base:
Litmus solution, phenolphthalein solution, methyl orange solution
(b) Classify the following given solution A and B in acidic and basic, giving reason.
SOLUTION A: [H+] < [OH-]
SOLUTION B: [H+] > [OH-] Solution
(a)
Indicator
Acid
Base
Litmus solution
Blue to red
Red to blue
Phenolphthalein
Colour-less
Pink
Methyl orange
Yellow
Pink
(a) Solution A is having more hydroxide ion showing that it is basic.
(b) Solution B is having more H+Â showing that its acidic.
Question 6
(a) A metal compound ‘X’ reacts with dil. H2SO4 to produce effervescence. The gas evolved extinguishes a burning candle. If one of the compound formed is calcium sulphate then what is ‘X’ and the gas evolved? Also, write a balanced chemical equation for the reaction which occurred.
(b)
(i) Name one antacid. How does it help to relieve indigestion in stomach?
(ii) A farmer treats the soil with quick lime or calcium carbonate. What is the nature of soil? Why does the farmer treat the soil with quick lime? Solution
(a) X is calcium carbonate and gas evolved is CO2
(b)
(i) NaHCO3 is antacid. It neutralizes excess of acid formed in the stomach.
(ii) The soil is acidic in nature. The farmer wants to make it neutral by adding quicklime which is good for crops.
Question 7
State what happens when sodium hydroxide solution reacts with dilute hydrochloric acid. What is this reaction called?
Question 8
Write the chemical name and formula of common salt. List two main sources of common salt in nature. Write any three uses of common salt. How is it connected to our struggle for freedom?
Question 9
An aqueous solution of sodium chloride is neutral but an aqueous solution of sodium is basic.
Question 10
What is chlor-alkali process? Write the chemical reaction taking place in the form of a balanced chemical equation. Name the gases liberated at the cathode and at the anode respectively. Solution
When concentrated solution of sodium chloride is electrolysed it forms Chlorine gas, Sodium hydroxide and Hydrogengas. It is called chlor-alkali process because of the products formed- Chlor for chlorine gas and alkali for Sodium hydroxide. Chlorine is formed at anode and Hydrogen is formed at the cathode and Na(OH)2 is formed near the cathode.
The main products formed are: Chlorine and Sodium Hydroxide
Question 11
Write chemical names and formulae of Plaster of Paris and gypsum.
Question 12
(a) What is baking soda? How is it known chemically?
(b) What is the nature of this salt?
(c) Write one application of it.
Question 13
How do metal carbonates and metal hydrogen carbonates react with acids?
Question 14
A metal carbonate X on reacting with an acid gives a gas which when passed through a solution Y gives the carbonate back. On the other hand, a gas G that is obtained at anode during electrolysis of brine is passed on dry Y, it gives a compound Z, used for disinfecting drinking water. Identify X, Y, G and Z. Solution
X is Calcium carbonate (CaCO3).
CaCO3 + Acid = Metal Salt + Water + CO2
If we take the acid as HCl then the reaction would be:
CaCO3 + 2HCl -------> CaCl2 + CO2 + H2O
Y is Lime water Ca(OH)2 or slaked lime.When this CO2 gas is passed through Lime water , the lime water turns milky due to the formation of Calcium Carbonate and thus it is formed again.
Ca(OH)2 + CO2 ---------> CaCO3 + H2O
The gas evolved at anode during electrolysis of brine is chlorine (G) When chlorine gas is passed through dry Ca(OH)2 (Y) produces bleaching powder (Z) used for disinfecting drinking water.
2Ca(OH)2 + 2Cl2 ------> Ca(OCl)2 + CaCl2 + 2H2O
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