NCERT Solutions for Class 10 Science Chapter 2 Acids Bases and Salts
Acids Bases and Salts Class 10 Questions and Answers
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts : In This Post, we will provide you NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts.
Acids, Bases and Salts Intext Questions with Answers
Page Number : 22
Q 1. Why should curd and sour substances not be kept in brass and copper vessels?
Ans. Curd and other sour substances contains acids which can react with the metals of brass and copper vessels to form toxic (poisonous) metal compounds which can cause food poisoning and damage our health.
Q 2. Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?
Ans. (i) Hydrogen gas is liberated when an acid reacts with a metal.
(ii) For example, Take some zinc granules in test tube. Add about 5 ml dilute hydrochloric acid slowly. Soon the reaction between zinc and hydrochloric acid starts and hydrogen gas is evolved.
(iii) Test For Hydrogen gas :
The gas evolved after reaction of acid with metal can be tested bringing a lighted candle near it. The gas burns with a pop sound, than it confirms the evolution of hydrogen gas.
Q 3. Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.
Ans. The gas thus formed is an effervescent carbon dioxide gas when calcium carbonate reacts with hydrochloric acid. The carbon dioxide gas also acts as an extinguisher for fires. Hence, the burning candle is extinguished. The metal compound A, therefore, constitutes calcium carbonate.
Page Number : 25
Q 1. Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?
Ans. H+ ions in aqueous solution are responsible for acidic character. HCL, HNO3, etc. give H+ ions in water While solutions of compounds like alcohol and glucose do not form any such ions so they do not show acidic characters.
Q 2. Why does an aqueous solution of an acid conduct electricity?
Ans. The aqueous solution of an acid conduct electricity due to the presence of charged particles called ions in it.
Q 3. Why does dry HCl gas not change the colour of the dry litmus paper?
Ans. In case of dry HCl gas, there is no presence of water and so, the dye on litmus paper cannot react with the gas. So, any dry gas will not give any change in the colour of litmus paper.
Dry HCl gas does not give H+ ions and therefore does not change the colour of dry litmus paper.
Q 4. While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
Ans. Dilution of concentrated acid is an exothermic process. If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. When the acid is added to water it recommended that the acid should be added to water and not water to the acid
Q 5. How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted?
Ans. The concentration of hydronium ions decreases when an acid is diluted because on adding water the H+ ions of the acid and hydroxyl ions of water react to form water molecules and the concentration of hydronium ions decreases. When an acid is diluted, then the concentration of hydronium ions decreases.
Q 6. How is the concentration of hydroxide ions (OH–) affected when excess base is dissolved in a solution of sodium hydroxide?
Ans. The concentration of hydroxide ions will increase when excess base is dissolved in a solution of sodium hydroxide, but it happens to a limited extent only after which the concentration becomes almost constant.
Page Number : 28
Q 1. You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic?
Ans. A pH value of less than 7 indicates an acidic solution, while greater than 7 indicates a basic solution. Therefore, the solution with pH = 6 is acidic and has more hydrogen ion concentration than the solution of pH = 8 which is basic.
Q 2. What effect does the concentration of H+ (aq) ions have on the nature of the solution?
Ans. The concentration of H+(aq) ions determines the acidic nature of solution. Hence, acidity of a solution increases with increase in concentration of H+ (aq) ions and vice versa.
Q 3. Do basic solutions also have H+(aq) ions? If yes, then why are these basic?
Ans. Yes basic solutions also have H+(aq) ions. They are basic because the concentration of hydroxide OH– is more than the H+(aq) ions.
Q 4. Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?
Ans. If the soil is acidic in nature which is not suitable for agriculture then the farmer would treat the soil with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate).
Page Number : 33
Q 1. What is the common name of the compound CaOCl2 ?
Ans. Bleaching Powder.
Q 2. Name the substance which on treatment with chlorine yields bleaching powder.
Ans. Slaked lime Ca(OH)2.
Q 3. Name the sodium compound which is used for softening hard water.
Ans. Sodium carbonate
Q 4. What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.
Ans. Sodium hydrogen carbonate (also known as sodium bicarbonate or bicarbonate of soda) has the chemical formula NaHCO3. When it is heated above about 80°C it begins to break down, forming sodium carbonate, water and carbon dioxide. This type of reaction is called a thermal decomposition.
Q 5. Write an equation to show the reaction between Plaster of Paris and water.
Acids, Bases and Salts Exercises Questions with Answers
Q 1. A solution turns red litmus blue, its pH is likely to be
(a) 1 (b) 4 (c) 5 (d) 10
Ans. (d) 10
Q 2. A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains
(a) NaCl (b) HCl (c) LiCl (d) KCl
Ans. (b) HCL
Q 3. 10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount HCl solution (the same solution as before) required to neutralise it will be
(a) 4 mL (b) 8 mL (c) 12 mL (d) 16 mL
Ans. (d) 16 mL
Q 4. Which one of the following types of medicines is used for treating indigestion?
Ans. (c) Antacid
Q 5. Write word equations and then balanced equations for the reaction taking
place when –
(a) dilute sulphuric acid reacts with zinc granules.
(b) dilute hydrochloric acid reacts with magnesium ribbon.
(c) dilute sulphuric acid reacts with aluminium powder.
(d) dilute hydrochloric acid reacts with iron filings.
(a) Zinc + dilute sulphuric acid → Zinc sulphate + Hydrogen
Zn (s) + H2SO4 (aq) → ZnSO4 (aq) + H2 (g)
(b) Magnesium ribbon + dil. Hydrochloric acid → Magnesium chloride + Hydrogen
Mg (s) + 2 HCl (aq) → MgCl2 (aq) + H2 (g)
(c) Aluminium powder + dil. Sulphuric acid > Aluminium sulphate + Hydrogen
2Al (s) + 3H2SO4 (aq) → Al2 (SO4)3 (aq) + 3H2 (g)
(d) Iron filings + Dilute hydrochloric acid > Ferric chloride + Hydrogen
2Fe (s) + 6HCl (aq) → 2FeCl3 (aq) + 3H2 (g)
Q 6. Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it.
Ans. Compounds like alchol and glucose contain hydrogen but do not ionise in the solution to produce H+ on passing through them.
Take a beaker of 250 ml and place two nails fixed with the help of cork.
- Connect the nails to the two terminals of a 6 volt battery as shown in figure.
- Now add some water containing ethanol and put the switch ON.
- Repeat the experiment with glucose solution. Observation : K The bulb will not glow and the needle of ammeter will not show deflection because glucose and ethanol do not conduct electricity.
The experiment shows glucose and ethanol do not ionise in aqueous solution, that is, they do not give H+ ions, therefore cannot conduct electricity. Thus, glucose and ethanol are not categorised as acids.
Q 7. Why does distilled water not conduct electricity, whereas rain water does?
Ans. The availability of ions is very important to conduct electricity. Distilled water is a pure type of water which does not contain any ions in it. Whereas rainwater contains dissolved gasses such as SO2, CO2.
These gases dissolve in water to form some kind of acids like carbonic acids which dissociates to give ions. Thus rainwater is conducting electricity while distilled water is not conducting electricity.
Q 8. Why do acids not show acidic behaviour in the absence of water?
Ans. The acidic behaviour of acid is due to the presence of hydrogen ions. The acids will not show its acidic behaviour in the absence of water, this is because acids do not dissociate to produce H+ (aq) ions in the absence of water.
Q 9. Five solutions A,B,C,D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9, respectively. Which solution is
(b) strongly alkaline?
(c) strongly acidic?
(d) weakly acidic?
(e) weakly alkaline?
Arrange the pH in increasing order of hydrogen-ion concentration.
Q 10. Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test tube B. Amount and concentration taken for both the acids are same. In which test tube will the fizzing occur more vigorously and why?
Ans. Hydrochloric acid and acetic acid and both react with magnesium. The hydrogen produced in both the reaction results fizzing. The more fizzing is observed in case of reaction of magnesium with Hydrochloric acid as HCl is more reactive than acetic acid.
Q 11. Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.
Ans. The pH value of milk is 6 since it is acidic in nature. When the milk is converted into curd due to the action of bacteria, lactic acid is formed which is more acidic in nature. Therefore the pH value of the milk is reduced as it turns to curd.
Q 12. A milkman adds a very small amount of baking soda to fresh milk.
(a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
(b) Why does this milk take a long time to set as curd?
Ans. (a) Milk is made slightly alkaline so that it may not get sour easily due to the formation of lactic acid in it.
(b) The alkaline milk takes a longer time to set into curd because the lactic acid being formed has to first neutralise the alkali present in it.
Q 13. Plaster of Paris should be stored in a moisture-proof container. Explain why?
Ans. Plaster of Paris in contact with moisture (water) changes to solid hard mass, gypsum. Therefore, it gets wasted. Hence it should be stored in moisture proof containers.
Q 14. What is a neutralisation reaction? Give two examples.
Ans. An acid neutralizes a base when they react with each other and respective salt and water are formed. The reaction between an acid and a base to give a salt and water is known as a neutralisation reaction.
Q 15. Give two important uses of washing soda and baking soda.
Uses of Washing Soda :
(i) Sodium carbonate (washing soda) is used in glass, soap and paper industries.
(ii) Sodium carbonate can be used as a cleaning agent for domestic purposes.
Uses of Baking Soda
(i) Baking Soda is used as an antacid in medicines to remove acidity of stomach.
(ii) Baking Soda is used for making baking powder (used in making cakes, bread, etc.).
NCERT Solutions for Class 10 Science Chapter 2 Acids Bases and Salts