HSLC Class 10 Science Chapter 2 Acids-Bases and Salts Solutions

INTEXT QUESTIONS AND ANSWERS || HSLC Class 10 Science Chapter 2 Acids-Bases and Salts Solutions 

 

Page No – 18

 

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 ?

Ans: If red litmus paper to all three test tubes , the test tube in which red litmus changes into blue contains basic solutions . Use this blue litmus paper to test the solutions in other two test tubes. The test tube in which there is no change will contain water.

 

HSLC Class 10 Science Chapter 2 Acids-Bases and Salts Solutions

 

Page No – 22

 

1. Why should curd and sour substances not be kept in brass and copper vessels ?

Ans : Curd and sour substances are acidic and acids react with copper vessels and brass to form toxic compounds . So, curd and sour substances are not kept in brass and copper vessels . HSLC Class 10 Science Chapter 2 Acids-Bases and Salts Solutions 

 

 

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. H 2 gas is liberated when an acid reacts with a metal.

ii. Illustrations : Set up an apparatus as shown . take some zinc granules in the test tubes. Add about 5 m L dilute hydrochloric acid slowly. soon the reaction between zinc and hydrochloric acid starts and hydrogen gas is involved.

iii. Test for H₂ gas : H₂ gas is not soluble in water , when passed through soap solution , if gets trapped into bubbles which burn with explosion .

 

 

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 a calcium chloride.

Ans: Metal compound A is Ca CO ₃

Gas evolved is CO ₂

Balanced equation

Ca CO ₃ (s) + 2 H Cl (aq) ———> Ca Cl ₂ (aq) + CO ₂ (g) + H ₂ O (l)

 

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Page No – 25 || HSLC Class 10 Science Chapter 2 Acids-Bases and Salts Solutions 

1. Why do H Cl , H NO ₃ etc , show acidic characters in aqueous solution while solutions of compounds like alcohol and glucose do not show acidic character ?

Ans : H⁺ ions in aqueous solution are responsible for acidic character . H Cl , H NO ₃ etc. generate H⁺ ions in water while C₂ H₅ OH and glucose do not do so and hence do not show acidic character.

 

 

2. Why does an aqueous solution of an acid conduct electricity ?

Ans: Acid when forms a solution in water , gets ionised , due to the presence of these ions electricity is conducted through it.

 

 

3. Why does dry HCl gas not change the colour of the dry litmus paper ?

Ans: Dry HCl    gas does not generate H⁺ ions and hence does not change the colour of dry litmus paper.

 

HSLC Class 10 Science Chapter 2 Acids-Bases and Salts Solutions

4. While diluting an acid , why is it recommended that the acid should be added to water and not water to the acid ?

Ans: When acid and water mix ,the reaction is highly exothermic , the acid may splash , cause burns and even the container can break . To avoid this and allow the heat evolved to be absorbed by  water . Slowly acid is added to water for diluting it. HSLC Class 10 Science Chapter 2 Acids-Bases and Salts Solutions 

5. How is the concentration of hydronium ions (H ₃ O ⁺ ) affected when a solution of an acid is diluted ?

Ans: When a given amount of an acid is added to water there area fixed number of hydronium ions per unit volume of the solution . On dilution the number of hydronium per unit volume decreases and concentration of hydronium ion decreases.

 

 

6. How is the concentration of hydroxide ions (OH^–) affected when excess base is dissolved in a solution of sodium hydroxide ?

Ans: When base is mixed with water there is decrease in the concentration of OH^– ions per unit volume.

 

 

Page No – 28 || HSLC Class 10 Science Chapter 2 Acids-Bases and Salts Solutions 

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 acidic and which one is basic ?

Ans : Solution A has more hydrogen ion concentration . Solution A is slightly acidic and solution B slightly basic.

 

 

2. What effect does the concentration of H⁺ (aq) ions have on the nature of the solution ?

Ans: If a solution has highly concentration of H⁺ ions it is more acidic in nature.

 

 

3. Do basic solutions also have H⁺ (aq) ions ? If yes , then why  are these basic ?

Ans: Yes , basic solution also have H⁺ ions but they are basic in nature due to more number of OH^– ions.

 

 

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: Plants work well in the pH range 6 – 8 . So when the soil becomes acidic, farmers treat the soil fields with bases like quick lime or slaked lime or chalk.

 

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Page No – 33 || HSLC Class 10 Science Chapter 2 Acids-Bases and Salts Solutions 

1. What is the common name of the compound CaOCl₂ ?

Ans : The common name of CaOCl₂ is bleaching powder and chemical name calcium oxychloride.

 

 

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

Ans : Calcium hydroxide [Ca(OH)₂] when treated with chlorine yields bleaching powder.

Ca(OH)₂ + Cl₂ ———–> CaOCl₂ + H₂O

 

HSLC Class 10 Science Chapter 2 Acids-Bases and Salts Solutions

3. Name the sodium compound which is used for softening hard water .

Ans: Sodium Carbonate.

 

 

4. What will happen if a solution of sodium hydrocarbonate is heated ? Give the equation of the reaction involved .

ans: When sodium hydrocarbonate is heated , sodium carbonate , water and carbon dioxide gas is obtained .

2 NaHCO₃ —–(heat)—–> Na₂CO₃ + H₂O + CO₂

 

 

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

Ans : 2 CaSO₄ . 1/2 H₂O + H₂O ————> 2 CaSO₄ . 2 H₂O

 

 

 

TEXT BOOK EXERCISES || HSLC Class 10 Science Chapter 2 Acids-Bases and Salts Solutions 

 

1. A solution turns red litmus blue , its pH is likely to be

1. 1
2. 4
3. 5
4. 10

Ans: d. 10

 

 

2. A solution reacts with crushed egg – shells to give a gas that turns lime water milky . The solution contains

1. NaCl
2. HCl
3. LiCl
4. KCl

Ans: b. HCl

 

 

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 required to neutralise it will be

1. 4 mL
2.  8 mL
3. 12 mL
4. 16 mL

Ans : d. 16 mL

 

 

4. Which one of the following types of medicines is used for treating indigestion ?

1. Antibiotic
2. Analgesic
3. Antacid
4. Antiseptic

Ans : c. Antacid

 

 

5. Write word equations and then balanced equations for the reaction taking place when –

1. dilute sulphuric acid reacts with zinc granules.
2. dilute hydrochloric acid reacts with magnesium ribbon.
3. dilute sulphuric acid reacts with aluminium powder.
4. dilute hydrochloric acid reacts with iron filings.

Ans:

a.  step I  Zinc granule + dilute hydrochloric acid ———-> Zinc chloride + hydrogen gas

step II  Zn (s) + dil HCl (aq) ———–> ZnCl₂ (aq) + H₂(g)

step III  Zn (s) + 2 HCl (aq) ———–> ZnCl₂ (aq) + H₂(g)

 

b.   step I  Magnesium + dilute Hydrochloric acid  ——–> magnesium chloride + hydrogen gas

step II  Mg (s) + dil HCl (aq) ———> MgCl₂ (aq) + H₂ (g)

step III  Mg (s) + 2 HCl (aq) ———-> MgCl₂ (aq) + H₂ (g)

 

c.  step I  Aluminium + dilute sulphuric acid ——–> Aluminium sulphate + Hydrogen gas

step II  Al (s) + dil H₂SO₄ ———-> Al₂ (SO₄)₃ + H₂ (g)

step III   2Al (s) + 3H₂SO₄(aq) ———-> Al₂(SO₄)₃(aq) +H₂ (g)

 

d. step I  Iron + dilute hydrochloric acid ——-> Iron chloride + Hydrogen

step II  Fe (s) + dil HCl (aq) ———> FeCl₂ (aq) + H₂ (g)

step III Fe(s) + 2HCl (aq) ——-> FeCl₂ (aq) + H₂ (g)

 

6. Compounds such as alcohol and glucose also contain hydrogen but are not categorised as acids. Describe an activity to prove it.

Ans : Take a beaker and keep and cork in it with two nails fixed on it. Connect the nails to the battery , bulb and key as shown in the figure. Now add ethanol in it and record your observation repeat the same set up for glucose and record your observations .

Observation : The bulb will not glow because charge is not flowing through it .

Conclusion : The experiment shows that glucose and ethanol do not ionise , H⁺ ions are not released , therefore they do not conduct elctricity. HSLC Class 10 Science Chapter 2 Acids-Bases and Salts Solutions 

 

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HSLC Class 10 Science Chapter 2 Acids-Bases and Salts Solutions

 

7. Why does distilled  water not conduct electricity, whereas rain water does ?

Ans : Rain water contains ions of acids and so it conducts electricity whereas there are no ions in distilled water.

 

 

8. Why do acids not show acidic behaviour in the absence of water ?

Ans: Acids in water give hydronium ions 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.

 

 

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

1. neutral
2. strongly alkaline
3. strongly acidic
4. weakly acidic
5. weakly alkaline

Arrange the pH in increasing order of hydrogen – ion concentration.

Ans : a. D     b. C     c. B     d. A      e. E

pH values in increasing order of hydrogen – ion concentration :

11< 9 < 7< 4< 1 .

 

 

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 : In test tube A  hydrochloric acid is present  which is a strong acid as compared  to acetic acid  in test tube B. The fizzing occurs more vigorously in test tube A as HCl is strong and dissociates completely into H⁺ and Cl^– ions for the reactions.

 

 

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 : pH of milk falls below 6 as it turns into curd due to the formation of lactic acid during this process.

 

 

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. pH is shifted to alkaline so that milk does not spoil by becoming curd and does not release lactic acid . The formation of lactic acid is prevented by adding baking soda which is alkaline in nature.

b. Milk will take long time to set as curd because milk is made alkaline by addind baking soda and the lactic acid released , if any will get neutralised by the alkali and slowly it will become acidic .

HSLC Class 10 Science Chapter 2 Acids-Bases and Salts Solutions

 

13. Plaster of Paris should be stored in a moisture – proof container. Explain why ?

Ans: Plaster of Paris is Calcium sulphate hemihydrate ( CaSO₄ . 1/2 H₂O). On exaposure to moisture it absorbs moisture and becomes gypsum (CaSO₄ . 2H₂O) which does not have the required setting property.

 

HSLC Class 10 Science Chapter 2 Acids-Bases and Salts Solutions 

14. What is a neutralisation reaction ? Give two examples .

Ans : The reaction in which acid reacts with base ( loses their property ) to form salt and water is called neutralisation reaction. e.g ;

i. HCl (aq) [acid] + NaOH (aq) [base]——–> NaCl [salt] + H₂O [water]

ii. HCl (aq) + KOH (aq) ————> KCl + + H₂O

 

HSLC Class 10 Science Chapter 2 Acids-Bases and Salts Solutions

15. Give two important uses of washing soda and baking soda.

Ans : Uses of washing soda :

i. It is used in glass , soap and paper industries.

ii. It is used to remove permanent hardness of water.

Uses of baking soda :

i. It is used as an antacid .

ii. It is used in soda , acid , fire extinguisher.

 

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HSLC Class 10 Science Chapter 2 Acids-Bases and Salts Solutions

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