Chapter 2 Science Class 10 Acids Bases and Salts

Chapter 2 Science Class 10 Acids Bases and Salts

Chapter 2 Acids Bases And Salts Class 10, In-text Questions, Textbook Questions, Summary, Exercise Solutions.

In-text Questions

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 three test tubes are treated with red litmus paper. The solution which turns red litmus paper into the blue is basic. Now this blue litmus paper is dipped in the remaining two solutions, the solution which turns this paper into red again is acidic and the solution in a third test tube is distilled water which is neutral so this does not react with litmus paper.

NCERT Solutions for Class 10 Science Chapter 2 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 the surface of brass and copper metal and form poisonous compounds/salt due to the presence of acids. These compounds are harmful to our body, So curd and sour substances are not to be kept in brass and copper vessels.

Question. 2. Class 10 Science Chapter 2 Question Answer

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 react with the metal. Example- Zinc sulphate and Hydrogen gas is produced by the reaction of sulphuric acid with zinc.

Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g)

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

 

Question. 3. Class 10 Science Chapter 2 Question Answer

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. One of the compounds formed in the reaction is the calcium chloride sol 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-

CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)

NCERT Solutions for Class 10 Science Chapter 2 Page 25

Question. 1. Why do HCI, 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 give H+ ions 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. Class 10 Science Chapter 2 Question Answer

Why does an aqueous solution of acid conduct electricity?

Answer- Acids conduct electricity in an aqueous solution due to the presence of free H+ ions.

Question. 3. Class 10 Science Chapter 2 Question Answer

Why does dry HCI 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 HCI gas does not change the colour of the dry litmus paper.

Read Also

NCERT Class 10th Science Chapter 1

Question. 4. Class 10 Science Chapter 2 Question Answer

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, acid should be added to water, not water to the acid because the process of dissolution of acid or base in water is highly exothermic. So concentrated acid should be added to 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 the glass container may also break due to local heating.

Question. 5. Acids Bases and Salts Class 10

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 has been 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. Acids Bases and Salts Class 10

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, increases the concentration.

Acids Bases and Salts Class 10 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. Acids Bases and Salts Class 10

What effect does the concentration 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 proportional H+ (aq) Ion concentration

Question. 3. Acids Bases and Salts Class 10

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. Chapter 2 Science Class 10

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.

Chapter 2 Science Class 10 Page 33

Question. 1. What is the common name of the compound CaOCI2?

Answer- The common name of the compound CaOCI2 is bleaching powder.

Question. 2. Chapter 2 Science Class 10

Name the substance which on treatment with chlorine yields bleaching powder.

Answer- Dry slaked lime or calcium hydroxide Ca(OH)2 gives bleaching powder when treated with chlorine gas.

Ca(OH)2 + Cl2 → CaOCI2 + H2O

Question. 3. Chapter 2 Science Class 10

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. Chapter 2 Science Class 10

What will happen if a solution of sodium hydro carbonate is heated? Give the equation for the reaction involved.

Answer- When the solution of sodium hydro carbonate is heated it gives Na2CO3.H2O and CO2 gas.

2NaHCO3 Heat → Na2CO3(s) + H2O(g) + CO2(g)

Question. 5. Chapter 2 Science Class 10

Write an equation to show the reaction between Plaster of Paris and water.

Answer- Plaster of Paris is a white powder, gives Gypsum on adding water, which is a hard and solid substance.

CaSO4.1/2H2O + 3/2H2O → CaSO4.2H2O(s)

Textbook Questions

Chapter 2 Science Class 10 Acids Bases and Salts

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. Chapter 2 Science Class 10

A solution reacts with crushed eggshells to give a gas that turns limewater milky. The solution contains-

(a) NaCl

(b) HCI

(c) LiCl

(d) KCl

Answer- (b) HCI

Question. 3. Chapter 2 Science Class 10

10 ml of a solution of NaOH is found to be completely neutralized by 8 ml of a given solution of HCI. If we take 20 ml 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. Chapter 2 Science Class 10

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. Chapter 2 Science Class 10

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 aluminum powder.

(d) dilute hydrochloric acid reacts with iron filings.

Answer

(a) Zinc + Dilute Sulphuric acid → Zinc sulphate + Hydrogen

Zn(s) + H2SO4 (dil) → ZnSO4(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 acid → Iron chloride + Hydrogen

Fe(s) + 2HCl(aq) → FeCl2(aq) + H2(g)

Question. 6. Acids Bases and Salts Class 10

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 do not ionize in solution and H+ ions are not produced. This is proved by the following activity-

Acids Bases and Salts class 10

Fig.: Acid solution in water conducts electricity

(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 the 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 the bulb does not glow in every case. In the 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 categorized as acids.

Question. 7. Acids Bases and Salts Class 10

Why does distilled water not conduct electricity, whereas rainwater 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 rainwater dissolves acidic gases like CO2, etc. which dissolve to form carbonic acid and as a result makes the rainwater acidic and releases H+ ions. So this conducts electricity.

Question. 8. Acids Bases and Salts Class 10

Why do acids not show acidic behavior in the absence of water?

Answer- Acids give hydronium ions in water which are responsible for their acidic behavior but in the absence of water acids, do not generate hydronium ions and thus, do not show acidic behavior.

Question. 9. Acids Bases and Salts Class 10

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. Acids Bases and Salts Class 10

Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCI) 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 the 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 react with Mg and give H2 gas. But in comparison to CH3COOH, the concentration of H+ ion is more in HCI. Therefore, HCl being strong acid will react vigorously, and hence more fizzing will occur.

Question. 11. Acids Bases and Salts Class 10

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. Acids Bases and Salts Class 10

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 the value of pH increases because baking soda, (NaHCO3) which is also called sodium hydrogen carbonate, is alkaline. This is a salt of a weak acid and a strong base so the solution becomes alkaline. Due to this reason, the lactate acid formed in the preservation of milk is neutralized so milk will not spoil early.

(b) Milk containing baking soda takes 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 takes a long time to convert into curd.

Question. 13. Acids Bases and Salts Class 10

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 a hard solid substance, Gypsum. So it should be stored in a moisture-proof container.

CaSO4 .1/2H2O + 3/2H2O → CaSO4.2H2O

CaSO4 .1/2H2O = Plaster of Paris                   

CaSO4.2H2O = Gypsum

Question. 14. Acids Bases and Salts Class 10

What is a neutralization reaction? Give two examples.

Answer- Neutralisation reaction- When an acid reacts with a base, then salt and water are formed. This is called a neutralization reaction.

Acid + Base → Salt + Water

In this reaction, acid and base cancel the effect of each other.

Examples

(1) NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

(2) KOH(aq) + HNO3(aq) → KNO3(aq) + H2O(l)

Question. 15. Acids Bases and Salts Class 10

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 antacids because being alkaline it neutralises excess acid in the stomach and provides relief.

Summary

NCERT Class 10 Science Chapter 2 Exercise Solutions

(1) Acids are sour in taste and turns blue litmus paper into red.

(2) Bases are bitter in taste and turn red litmus paper into blue.

(3) Acid-base indicators are dyes or mixtures of dyes which are used to indicate the presence of acids and bases.

(4) The substances whose odour changes in acidic or basic media are called olfactory indicators

(5) Litmus solution is a purple dye, which is extracted from lichen, a plant belonging to the division Thallophyta, and is commonly used as an indicator.

(6) Acids forms H+(aq) ions in aqueous solution and bases forms OH(aq) ions in aqueous solution.

(7) When an acid reacts with a metal, hydrogen gas is evolved and a corresponding salt is formed.

(8) When a base reacts with a metal, along with the evolution of hydrogen gas a salt is formed but such reactions are not possible with all metals.

Zn(s) + 2NaOH(aq) → Na2ZnO2(s) + H2(g)

Na2ZnO2 = (Sodium zincate)

(9) When an acid reacts with a metal carbonate or metal hydrogen carbonate, it gives the corresponding salt, carbon dioxide gas and water.

Na2CO(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + CO2(g)

NaHCO3(s) + HCl(aq) → NaCl(aq) + H2O(l) + CO2(g)

(10) Neutralisation reaction- Acids and Bases reacts with each other to form salt and water, this reaction is called neutralisation reaction. This is exothermic reaction.

NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

(11) Metal oxides are generally basic so they react with acids and form salt and water.

(12) Non-metal oxides are acidic so they react with bases and form salt and water.

(13) Aqueous solution of acids, bases, and salts conduct electricity because free ions are present in these solutions due to which current is passed.

(14) Alkali- Bases which are soluble in water are called Alkali. These are corrosive in Nature.

(15) When water is added in Acidic or Basic solution, (H3O+/OH) ion concentration per unit volume is decreased. This process is called dilution.

(16) The process of dissolving an acid or a base in water is a highly exothermic one.

(17) The strength of an acid or a base can be tested by using a scale called the pH scale (0-14) which gives the measure of hydrogen ion concentration in a solution.

(18) A neutral solution has a pH of exactly 7, while an acidic solution has a pH less than 7 and a basic solution has a pH of more than 7.

(19) Acids are of two types- strong acid and weak acid. The acids which give more number of H+ ion in solution are called strong acids and the acids which give less number of H ion in solution are called weak acids.

(20) Similar to acids, bases are also of two types- strong base and weak base which gives more and less number of OH ions in solution respectively.

NCERT Class 10 Science Chapter 2 PDF Click Here to Download

(21) Living beings carry out their metabolic activities within an optimal pH range.

(22) Acid rain- When the pH of rainwater becomes less than 5.6 then this is called acid rain. The survival of aquatic life in such water becomes difficult.

(23) Tooth decay starts when the pH of the mouth is lower than 5.5.

(24) The pH of solutions of different salts are different which depends on the acid and base by which that salt is formed. For example pH of the solution of salt formed with strong acid and strong base is 7.

NCERT Class 10 Science Chapter 2 Exercise Solutions

(25) The common salt is an important raw material for various materials of daily use, such as sodium hydroxide, baking soda, washing soda, bleaching powder, and many more.

(26) Chlor-alkali Process- When electricity is passed through an aqueous solution of sodium chloride, it decomposed to form NaOH, this process is called chlor-alkali process. Cl2 and H2 are also formed in this process.

(27) Bleaching Powder (CaOCI2) is used for bleaching clothes etc. and for disinfecting drinking water.

(28) Bleaching Powder is prepared by the reaction of dry slaked lime with chlorine.

Ca(OH)2 + Cl2 → CaOCI2 + H2O

(29) The formula of washing soda is Na2CO3 .10H2O, baking soda is NaHCO3, and Plaster of Paris is CaSO4.1/2 H2O.

NCERT Class 10 Science Chapter 2 Exercise Solutions

(30) Salts are very useful in everyday life and industries. Large crystals of NaCl are brown due to impurities, this is called rock salt.

(31) Water of crystallisation- The fixed number of water molecules present in one formula unit of salt in its crystalline form is called water of crystallisation.

(32) The formula of Gypsum is CaSO4 .2H2O. On heating gypsum it loses water molecules and becomes calcium sulphate hemihydrate (CaSO4.1/2 H2O). This is called Plaster of Paris.

(33) Plaster of Paris is used for making toys, materials for decoration, etc.

 

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