RBSE Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts

Rajasthan Board RBSE Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts Textbook Exercise Questions and Answers.

RBSE Class 10 Science Solutions Chapter 2 Acids, Bases and Salts

RBSE Class 10 Science Chapter 2 Acids, Bases and Salts InText Questions and Answers

Page 18:

Question 1.
You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?
Answer:
The solutions of all the three test tubes is treated with red litmus paper. The solution which turns red litmus paper into blue is basic. Now this blue litmus paper is dipped in remaining two solutions, the solution which turns this paper into red again is acidic and solution in third test tube is distilled water which is neutral so this does not react with litmus paper.

Page 22:

Question 1.
Why should curd and sour substances not be kept in brass and copper vessels?
Answer:
Curd and sour substances are acidic so if these are kept in brass and copper vessels then these will react with surface of brass and copper metal and form poisonous compounds salt due to the presence of acids. These compounds are harmful for our body so curd and sour substances are not to be kept in brass and copper vessels.

Question 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?
Answer:
Hydrogen gas is released when the acids reacts with the metal. Example: Zinc sulphate and Hydrogen gas is produced by die reaction of sulphuric acid with zinc.

For the testing the presence of Hydrogen gas it is passed in the solution of soap, then bubbles are formed and when burning candle is brought near the mouth of the test tube, this gas bums with blue flame and POP sound.

Question 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.
Answer:
Metal compound ‘A’ is calcium carbonate. The one of the compound formed in the reaction is calcium chloride so compound contains calcium. The gas evolved extinguishes a burning candle which is CO₂ so the reaction of compound A (CaCO₃) with dilute hydrochloric acid will be as follows:

Page 25

Question 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?
Answer:
HCl and HNO₃ get ionized in their aqueous solutions and ,produce H⁺ ions and anions. So these show acidic character because acids gives H⁺ ion in aqueous solution but alcohol and glucose are covalent compounds and do not produce free H⁺ ions in solutions. So these do not show acidic character.

Question 2.
Why does an aqueous solution of an acid conduct electricity?
Answer:
Acids conduct electricity in aqueous solution due to the presence of free H⁺ ions.

Question 3.
Why does dry HCl gas not change the colour of the dry litmus paper?
Answer:
Dry HCl gas does not show ionization so it does not contain H⁺ ions therefore, HCl gas shows its acidic character only in presence of water. So due to absence of H⁺ ions dry HCl gas does not change the colour of the dry litmus paper.

Question 4.
While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
Answer:
While diluting an acid, add should be added to water, not water to the add because process of dissolution of add or base in water is highly exothermic. So concentrated add should be added in water carefully and it must always be added slowly to water with constant stirring. Opposite to this if water is added in concentrated acid the mixture may splash out due to heat generated during the process which may be harmful to the person present near to this and glass container may also break due to local heating.

Question 5.
How is the concentration of hydronium ions (H₃O⁺) affected when a solution of an acid is diluted?
Answer:
When a solution of an acid is diluted means water is added the concentration of H₃O⁺ decreases as the volume of the solution increases due to unionized water. Therefore, the number of hydronium ions per unit volume decreases. So H₃O⁺ ion concentration decreases continuously.

Question 6.
How is the concentration of hydroxide ions (OH^–) affected when excess base is dissolved in a solution of sodium hydroxide?
Answer:
When excess base is dissolved in a solution of sodium hydroxide concentration of (OH⁺) per unit volume increases because the OH obtained from the base added, increase the concentration.

Page 28.

Question 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?
Answer:
Solution ‘A’ is acidic (pH = 6) because solution will be acidic when pH is less than 7 solution ‘B’ is basic (pH = 8) because solution will be basic when pH is more than 7. Solution ‘A’ will have more hydrogen ion concentration because pH decreases with increase in hydrogen ion concentration.

Question 2.
What effect does the concen-tration of H⁺ (aq) ions have on the nature of the solution?
Answer:
Solution becomes more acidic with increase in H⁺ ion concentration and it becomes less acidic means basic character increases with decrease in H⁺ ion concentration. Acidic character oc H⁺(aq) Ion concentration

Question 3.
Do basic solutions also have H⁺(aq) ions? If yes, then why are these basic?
Answer:
Yes, basic solutions also have H⁺ ions (aq) but in basic solution H⁺(aq) are not in free state and equilibrium exists between H+ and OH . The basic solution contains more OH⁺ (aq) ions than H⁺(aq). Hence the solution is basic.

Question 4.
Under what soil condition do you think a farmer would treat the soil of his fields with quicklime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?
Answer:
A farmer would treat the soil of his fields with quicklime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate) when the soil becomes acidic more than required because these substances are basic in nature, which will neutralise the acidity of soil.

Page 33.

Question 1.
What is the common name of the compound CaOCl₂?
Answer:
The common name of the compound CaOCl₂ is bleaching powder.

Question 2.
Name the substance which on treatment with chlorine yields bleaching powder.
Answer:
Dry slaked lime or calcium hydroxide Ca(OH)₂gives bleaching powder when treated with chlorine gas.
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

Question 3.
Name the sodium compound which is used for softening hard water.
Answer:
Sodium carbonate (or washing soda) Na₂CO₃ 10H₂O is used for the softening of hard water with the help of this permanent hardness of water is removed.

Question 4.
What will happen if a solution of sodium hydrocarbonate is heated? Give the equation for the reaction involved.
Answer:
When the solution of sodium hydrocarbonate is heated it gives Na₂CO₃, H₂O and CO₂ gas

Question 5.
Write an equation to show the reaction between Plaster of Paris and water.
Answer:
Plaster of Paris is white powder, gives Gypsum on adding water, which is hard and solid substance.

RBSE Class 10 Science Chapter 2 Acids, Bases and Salts Textbook Questions and Answers

Question 1.
A solution turns red litmus blue, its pH is likely to be:
(a) 1
(b) 4
(c) 5
(d) 10
Answer:
(d) 10

Question 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
Answer:
(b) HCl

Question 3.
10 ml of a solution of NaOH is found to be completely neutralized by 8 mi of a given solution of HCl. If we take 20 mi of the same solution of NaOH, the amount of HCl solution (the same solution as before) required to neutralize it will be:
(a) 4 ml
(b) 8 ml
(c) 12 ml
(d) 16 ml
Answer:
(d) 16 ml.

Question 4.
Which one of the following types of medicines is used for treating indigestion?
(a) Antibiotic
(b) Analgesic
(c) Antacid
(d) Antiseptic
Answer:
(c) Antacid.

Question 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.
Answer:
(a) Zinc + Dilute Sulphuric acid → Zinc sulphate + Hydrogen
Zn(s) + H SO₄(dil) → ZnSO(aq) + H₂(g)↑

(b) Magnesium + Dilute Hydrochloric acid → Magnesium chloride + Hydrogen
Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)↑

(c) Aluminium + Dilute Sulphuric acid → Aluminium sulphate + Hydrogen
2Al(s) + 3H₂SO₄(aq) → Al₂(SO₄)₃(aq) + 3H₂(g)↑

(d) Iron + Dilute Hydrochloric add → Iron chloride + Hydrogen
Fe(s) + 2HCl(aq) → FeCl₂(aq) + H₂(g)↑

Question 6.
Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it.
Answer:
Compounds like alcohol and glucose have hydrogen but these does not ionise in solution and H+ ions are not produced. This is proved by the following activity

(1) Take solutions of glucose, alcohol, hydrochloric acid, sulphuric acid, etc.
(2) Fix two nails on a cork, and place the cork in a 100 mL beaker.
(3) Connect the nails to the two terminals of a 6 volt battery through a bulb and a switch as shown in figure.
(4) Now pour some dilute HCl in the beaker and switch on the current.
(5) Repeat the process with dilute sulphuric acid. What do you observe?
(6) Repeat the experiment separately with glucose and alcohol solutions.

Observation and Result:
We observe that bulb does not glow in every case. In case of acid due to the presence of ions bulb start glowing because the conduction of electricity is possible but not in the solution of glucose and alcohol; because ions are not present in these. Therefore, glucose and alcohol are not categorised as acids.

Question 7.
Why does distilled water not conduct electricity, whereas rain water does?
Answer:
Distilled water is completely pure. It does not contain any type of ionic compound, and therefore, it is neutral. Due to this reason distilled water does not conduct electricity. Whereas rain water dissolves acidic gases like CO₂, etc. which dissolve to form carbonic acid and as a result makes the rain water acidic and releases H⁺ ions. So this conducts electricity.

Question 8.
Why do acids not show acidic behaviour in the absence of water?
Answer:
Acids give hydronium ions in water which are responsible for their acidic behaviour but in the absence of water acids, do not generate hydronium ions and thus, do not show acidic behaviour.

Question 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:
(a) neutral?
(b) strongly alkaline?
(c) strongly acidic?
(d) weakly acidic?
(e) weakly alkaline?
Arrange the pH in increasing order of hydrogen-ion concentration.
Answer:
(a) Solution D is neutral, with pH = 7
(b) Solution C is strongly alkaline, with pH =11
(c) Solution B is strongly acidic, with pH = 1
(d) Solution A is weakly acidic, with pH = 4
(e) Solution E is weakly alkaline, with pH = 9
Increasing order of Hydrogen ion concentration is as follows :
Solution C < Solution E < Solution D < Solution A < Solution B. pH = 11 < pH = 9 < pH = 7 < pH = 4 < pH = 1

Question 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?
Answer:
Fizzing will occur more vigorously in test tube ‘A’. HCl and CH₃COOH both reacts with Mg and gives H₂ gas. But in comparision to CH₃COOH the concentration of H+ ion is more in HCl. Therefore, HCl being strong acid it will react vigorously and hence more fizzing will occur.

Question 11.
Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.
Answer:
The pH of fresh milk is 6, i.e., it is mildly acidic. When it ferments, lactic acid is formed which turns milk into curd. Due to lactic acid, its acidic property increases which further reduces its pH value.

Question 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?
Answer:
(a) When baking soda is added to milk the pH value of milk changes from 6 to slightly Alkaline means value of pH increases because baking soda, (NaHCO₃) which is also called sodium hydrogen carbonate, is alkaline. This is a salt of weak acid and strong base so solution becomes alkaline. Due to this reason the lactate acid formed in the preservation of milk is neutralised so milk will not spoil early.

(b) Milk containing baking soda take a long time to set as curd because turning of milk into curd is a fermentation process, which occurs at definite pH, approximately at pH 7 means medium should be neutral while pH is increased by the addition of NaHCO₃ (baking soda). Due to this reason process of formation of curd from milk becomes slow means more time is required to convert the milk from alkaline to acidic. So this milk take a long time to convert into curd

Question 13.
Plaster of Paris should be stored in a moisture-proof container. Explain why?
Answer:
When Plaster of Paris comes in contact with moisture, it reacts with water molecules and readily converts into hard solid substance, Gypsum. So it should be stored in moisture proof container.

Question 14.
What is a neutralisation reaction? Give two examples.
Answer:
Neutralisation reaction: When an acid reacts with a base, then salt and water are formed. This is called neutralisation reaction.
Acid + Base → Salt + Water
In this reaction, acid and base cancel the effect of each other.
examples:

Question 15.
Give two important uses of washing soda and baking soda.
Answer:
Uses of washing soda:
(1) Washing soda (sodium carbonate) is used in the manufacture of Borax.
(2) Washing soda is used in glass, soap and paper industries. It is also used as cleaning agent for domestic purposes.

Uses of baking soda:
(1) Baking soda (sodium hydrogen carbonate) is used in soda-acid fire extinguishers.
(2) Baking soda is also an ingredient in antacid because being alkaline it neutralises excess acid in the stomach and provides relief.