| Class | 10th |
| Subject | Science (NCERT) |
| Category | Important Questions |
Acid, Bases and Salt Class 10 Science Chapter 2 Important Question Answer
Q1. What happens when gypsum is heated to 373 K ? Give chemical equation for it.
Ans – On heating gypsum at 373 K, it loses water molecules and becomes calcium sulphate hemihydrate (CaSO4.½H2O). This is called Plaster of Paris, the substance which doctors use as plaster for supporting fractured bones in the right position.
ΔCaSO4.2H2O → CaSO4.½H2O + (3/2)H2O
Q2. What is the common name of CaOCl2 ? Give the chemical reaction by which it is prepared.
Ans – Common name of CaOCl2 is bleaching powder.
Preparation reaction of bleaching powder is as :
Ca(OH)2 + Cl2 → CaOCl2 + H2O
Q3. What is Acid Rain? How does it affect aquatic life?
Ans – When pH of rain water is less than 5.6, it is called acid rain. When acid rain flows into the rivers, it lowers the pH of the river water. The survival of aquatic life in such rivers becomes difficult.
Q4. What is chlor-alkali process? Explain with the help of a chemical equation. Most Important
Ans – When electricity is passed through an aqueous solution of sodium chloride (called brine), it decomposes to form sodium hydroxide. The process is called the chlor-alkali process because of the products formed– chlor for chlorine and alkali for sodium hydroxide.
2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2 (g) + H2 (g)
Chlorine gas is given off at the anode, and hydrogen gas at the cathode. Sodium hydroxide solution is formed near the cathode. The three products produced in this process are all useful.
Q5. Why does distilled water not conduct electricity, whereas rain water does ?
Ans – Distilled water does not conduct electricity because it does not contain ions while rain water conducts electricity as it contains ions due to presence of dissolved salts present in it.
Q6. While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid ?
Ans – The process of adding water to an acid is highly exothermic, therefore it is always recommended that acid should be added to water. If it is done the other way, then it might be possible that the mixture may splash out and cause burns because of the large amount of heat generated.
Q7. What is neutralisation reaction ? Give one example. Most Important
Ans – The reaction between an acid and a base to give a salt and water is known as a neutralisation reaction.
Base + Acid → Salt + Water
Example – NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
Q8. Why should curd and sour substances not be kept in Brass and Copper vessels ?
Ans – Curd and sour substances contain acids. When acid reacts with metal , it forms salt and hydrogen gas. When sour things, such as curd, are stored in brass or copper vessels, the lactic acid in the curd reacts with the metals, causing corrosion and the creation of toxic salts that cannot be digested.
Q9. Write common name and two uses of NaHCO3.
Ans – Common name of NaHCO3 is baking soda.
Two uses of Baking soda are as :
(i) For making baking powder.
(ii) Used in soda-acid fire extinguishers.
(iii) Used as ingredient in antacids.
Q10. Which Acid is present in tamarinds?
Ans – Tartaric acid
Q11. What is chemical formula of baking soda? Give chemical equation used in its preparation. Most Important
Ans – Chemical formula of baking soda is NaHCO3 .
Chemical equation : NaCl + H2O + CO2 + NH3 → NH4Cl + NaHCO3
Q12. What is the chemical formula of washing soda ? Give chemical equation used in its preparation.
Ans – Chemical formula of washing soda is Na2CO3.10H2O
Chemical equation : Na2CO3 + 10H2O → Na2CO3.10H2O
Q13. Give two important uses of washing soda and baking soda.
Ans – Two uses of Baking soda are as :
(i) For making baking powder.
(ii) Used in soda-acid fire extinguishers.
(iii) Used as ingredient in antacids.
Two important uses of washing soda are as :
(i) Washing soda is used in glass, soap and paper industries.
(ii) Used for removing permanent hardness of water.
(iii) Used in manufacture of sodium compounds such as borax.
Q14. Why do acids not show acidic behaviour in the absence of water?
Ans – Because in the absence of water, acids do not dissociate to produce H + ions. It is only in the presence of water, that acids dissociate and produce H + ions, which are responsible for the acidic behaviour of acids. Hence acids will not exhibit acidic behaviour in the absence of water.
Q15. What is pH scale in chemistry? Explain.
Ans – A scale for measuring hydrogen ion concentration in a solution, called pH scale. On the pH scale we can measure pH generally from 0 (very acidic) to 14 (very alkaline). The pH of a neutral solution is 7.
Q16. Four solution A, B, C and D when tested with a universal indicator, showed pH as 1, 7, 6 and 13 respectively Which solution is neutral, strongly alkaline, weak alkaline or weak acid and strongly acidic ?
Ans – pH of neutral solution = 7
pH of strongly alkaline = 13
pH of weak alkaline or weak acid = 6
pH of strongly acidic = 1
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