Class 10 Science Acid base and Salts Long Questions( Four Marks questions)
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Question 1) On passing excess CO2 through lime water, it first turns milky and then becomes colourless. Explain why? Write the chemical reactions. Solution
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 2) While eating food, you happen to spill some curry on your white shirt. You immediately scrub it with soap. What happens to its yellow colour on scrubbing with soap? Why? What happens to this stain when the shirt is washed with plenty of water? Question 3) Explain the action of dilute hydrochloric acid on the following with chemical equations:
(a) Magnesium ribbon
(b) Sodium hydroxide
(c) Crushed egg shells Solution
The formula equation for this experiment is:
g + 2HCl ->MgCl2 + H2
HCL + NaOH -> Nacl + H2O
Egg shells contains calcium carbonate, which on reaction with HCl liberates CO2 gas
CaCO3 + 2HCl ? CaCl2 + H2O + CO2
Question 4) What are products formed when an acid reacts with a base? What is the type of reaction? Give one example and name the salt obtained. Question 5) On adding dilute hydrochloric acid to copper oxide powder, the solution formed is blue - green.
(a) Identify the compound formed which gives blue -green colour to the solution.
(b) Write its balanced chemical equation.
(c) On the basis of above reaction, what should be the nature of copper oxide? Solution
When HCl reacts with copper oxide, a blue green solution of copper (II) chloride is formed. The reaction is as follows:
HCl + CuO --------> CuCl2 + H2O
(aq) (s) (aq) (l)
Question 6)Sugandha prepares HCI gas in her school laboratory using certain chemicals. She puts both dry and wet blue litmus papers in contact with the gas.
(i) Name the reagents used by Sugandha to prepare HCI gas.
(ii) State the colour changes observed with the dry and wet blue litmus paper.
(iii) Show the formation of ions when HCI gas combines with water. Question 7) How the following substances will dissociate to produce ions in their solution?
(a) Hydrochloric acid
(b) Nitric acid
(c) Sulphuric acid
(d) Sodium hydroxide
(e) Potassium hydroxide
(f) Magnesium hydroxide Solution
Question 8) Differentiate between strong electrolytes and weak electrolytes. Mention two examples of each. Question 9) State reasons for the following:
(a) A tarnished copper vessel begins to shine again rubbed with lemon.
(b)All alkalis are bases but all bases are not alkalis.
(c) Use of a mild base like baking soda on the honey – bee stung area gives relief. Question 10) (a) State what happens when an acid reacts with a base? Name the reaction and give equation of the reaction involved.
(b) Name one natural source of each of the following acids:
(i) Citric acid
(ii) Oxalic acid
(iii) Lactic acid
(iv) Tartaric acid
(v) Acetic acid Solution
citric acid in lemon
oxalic acid in tomato
lactic acid in curd
tartaric acid in tamarind
Acetic acid in vinegar
Question 11) A student mixed equal volumes of hydrochloride acid and sodium hydroxide solutions of same concentration.
(i) What would be the pH and colour of pH paper of the resulting solution and why?
(ii) Write the chemical equation of the reaction involved.
Question 12) State the colour change on treating pH paper with the folloing solutions:
sodium hydroxide solution, water, sulphuric acid solution, calcium hydroxide solution. Arrange the following solutions in increasing order of pH. Question 13) (a) Name the acid produced in our stomach. What happens when there is an excess secretion of acid in the stomach? How can its effect be cured?
(b) Explain how pH change is the cause of tooth decay? How it can be prevented?
(c) What is the ideal soil pH for the growth of plants? Explain with the help of an activity how will you test the pH of a sample of soil collected from your locality? Question 14) Name one indicator which specifies the various levels of H+ ion concentration. Question 15) A compound ‘X’ is a constitute of baking powder. It is used as an antacid. When ‘X’ is heated it gives out a gas ‘Y’ which when passed through lime water turns it milky and a salt ‘Z’ is formed which is the main constituent of washing powder. Identify ‘X’, ‘Y’ and ‘Z’. Write balanced chemical equations for the reactions involved. Question 16) How is Plaster of Paris chemically different from gypsum? How can they be interconverted? Write two uses of Plaster of paris. Question 17) Write one point of difference between each of the following:
(a) A hydrated salt and an anhydrous salt.
(b) Washing soda and soda ash.
(c) Baking soda and baking powder. Question 18)On the basis of their pH values, how will you identify neutral, acidic and basic salt solution? How are these salts prepared? Question 19) Give two uses each of sodium hydroxide, hydrogen and chlorine. Solution
Sodium hydroxide a)It is used for making soaps and detergents.
b)It is used for making artificial textile fibres(rayon)
a)Chlorine is used to sterilize drinking water and in swimming pool since it is a disinfectant.
b)It is used inthe production of bleaching powder and HCl.
Question 20)When this white powder is mixed with water a hard solid mass is obtained. Write balanced chemical equation for this change. Question 21)Write name of the compound:
(a) Used for softening hard water.
(b) Used as an antacid.
(c) Which is a component of washing soda.
(d) Which is used as an oxidizing agent in many chemical industries? Question 22) A gas X reacts with lime water and forms a compound Y which is used as a bleaching agent in chemical industry. Identify X and Y. Give the chemical equation of the reaction involved.
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