NCERT Class 10 Science Solutions Chapter Two Acids, Bases and Salts

NCERT Class 10 Science Solutions Chapter Two Acids, Bases and Salts

NCERT Class 10 Science Solutions Acids, Bases and Salts Chapter Intext and Exercise Questions. NCERT Class 10 Science Chapter Two Acids, Bases and Salts Solutions Download Free PDF NCERT Textbooks Solutions Class 10 Science Chapter 2 Acids, Bases and Salts.

NCERT Class 10 Science Solutions Chapter Two: Acids, Bases and Salts

Board:

NCERT
Class:

10

Subject

Science
Chapter

Two (2)

Chapter Name:

Acids, Bases and Salts

Page no. 18

(1) You have been provided with tree test tubes, one of them contains distilled water & other two contains an acidic solution & a basic solution respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?

Answer:- If the colour of red litmus paper gets changed to blue, than it is a base & if there is no colour change, then the solution is either acidic or neutral. Thus basic solution can be easily identified.

  • Now we mark the three test tubes A, B & C. A drop of solution in a test tube is kept on red litmus paper.
  • This process is repeated with solution B & C.
  • If one of them colour changes to blue, then that solution is basic.
  • Hence out of three one test tube is separated.
  • Now a drop of basic solution is mixed with a drop of another two solutions separately.
  • If the colour of red litmus turns blue then that solution is neutral.
  • If there is no colour change of red litmus, then the solution is acids.
  • This is due to the acidic & basic solutions neutralizes each other.
  • Thus, we can identify the contents of each test tube.

Page- 22

(1) Why should curd & sour substances not be kept in brass & Copper vessels.

Answer: when metals reacts with acids it forms poisonous metal salts with evolution of H2 gas curd & sour substances kept in brass & copper vessels, it forms poisonous metal salt & H2 gas This liberated H2 gas & metal salts produces the food poisoning & damage the food & it affects our health adversely.

Hence to protect the food from food poisoning curd & sour substances not be kept in brass & copper vessels.

(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: When an acid react with any metal it produce salt & hydrogen gas.

Take few pieces of zinc granules & add 5 ml of dilute H2SO4 shake it & pass the gas produced into a soap solution. The bubbles of the soap solution are formed these soap bubbles contain hydrogen gas.

H2SO4 + Zn -> Zn(SO4) + H2

We can test the evolved hydrogen gas by its burning with a pop sound when a candle is brought near the soap bubbles.

(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: CaCO3 + 2HCL -> CaCl2 + Co2 + 2H2o

Calcium Carbonate  Hydrochloric Acid  Calcium Chloride

Page no 25.

(1) Why do HCL, HNO3 etc show acidic characters in aqueous solutions white solutions of compounds like alcohol & glucose do not show acidic character?

Answer: When HCL, HNO3 etc are mixed with water, then they dissolve into water & forms H+ or H3O+ ions, which shows acidic character.

Whereas, when glucose or alcohol mixed with water then they do not dissolve in water & not forms H+ ions. Hence they do not shows acidic character.

Ex:- HCL (aq) —-> H+ + Cl

H+ + H2O –> H30+

(2) Why does an aqueous solution of an acid conduct electricity?

Answer: Aqueous solution of an acid contain hydrogen (H+) ions or hydronium ion (H30+) which are responsible for conduction of electricity. Hence, aqueous solution of an acid conduct electricity.

(3) Why does dry HCL gas not change the colour of the dry litmus paper?

Answer: Dry HCL does not produce H+ ions thus they does not shows acidic behaviour. Therefore dry HCL gas not changes the colour of dry litmus paper it remain same.

(4) While diluting an acid, why is it recommended that the acid should be added to water & not water to the acid?

Answer: While diluting an acid, it is recommended that the acid should be added to water & not water to acid because the process of dissolving an acid in water is exothermic process. If water is added to acid heat generated & release from the mixture that cause the mixture to splash or explosion & can cause burn to body parts also the glass container may break, which injures body parts.

(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, there is decrease in concentration of hydronium ions (H3O+) per unit volume.

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

Answer: The concentration of hydroxide ion (OH-) would increase when excess of base is dissolved in a solution of sodium hydroxide.

Page 28:

(1) You have two solutions, A & B. The PH of solution A is 6 & PH of solution B is 8. Which solution has more hydrogen ion concentration? Which solution has mote hydrogen ion concentration? Which of this is acidic & which one is basic?

Answer: Hydrogen ion concentration is depends on the PH solution. According to Ph scale, PH value less than 7 indicates acidic solution & PH value more than 7 indicate basic solution.

Hence solution A having PH = 6 is acidic & has more hydrogen ion concentration than solution ‘B’ having PH = 8 which is basic.

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

Answer: As the concentration of H+ (aq) ions increases, acidic nature of the solution increase & if the concentration of (aq) ions decreases acidic nature of the solution also decreases, & basic nature increases.

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

Answer: Basic solutions also have H+ (aq) ions, but they are in very less number as compare to the OH ions. As there are more number of OH ions which are responsible for basic nature hence that solution shows basic nature.

Page 28

(4) Under what 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)?

Answer: Quick lime (calcium oxide), slaked lime (calcium hydroxide), chalk (Calcium) all these compounds are basic in nature. Hence they are used or treat the soil of farmer’s field which is acidic in nature having low PH value of the soil.

Page no 33

(1) What is the common name of the compound CaoCl2?

Answer: The common name of the compound CaoCl2 is bleaching powder.

(2) Name the substance which on treatment with chlorine yields bleaching powder?

Answer: Calcium hydroxide [(CaCoH)2] on treatment with chlorine yields bleaching powder.

(3) Name the sodium compound which is used for softening hard water?

Answer: Washing soda (Na2Co3 . 10H2O) is used softening hard water.

Page no – 33

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

Answer: When a solution of sodium hydrocarbonate is heated, it produces sodium carbonate, water with evolution of carbon dioxide gas.

Exercise Questions

(Q1) A solution turns ted litmus blue, its pH is likely to be.

(a) 1

(b) 4

(c) 5

(d) 10

Ans:

(d) 10

Reason:-

  • Basic solution turns ted litmus blue & by pH scale. PH of basic solution is in between 7 to 10.

(Q2) A solution react with crushed egg-shells to give a gas that turns lime-water milky the solution contains.

(a) NACL

(b) HCL

(c) RICL

(d) KCL

Ans:

(b) HCL

Reason:- In egg-shell calcium carbonate (CaCo3) is present. This CaCo3 react with HCL, it liberates Co2 gas which turns lime-water milky.

Reaction:-

Caco3 + 2Hcl -> Cacl2 + H2O + Co2

Calcium Carbonate + hydrochloric acid -> calcium chloride carbon dioxide

(Q3) 10 ML of solution of NAOH is found to be completely neutralized by 8 mL of a given solution of HCL. If we take 20ML of the same solution of NaOH, the amount HCL solution (the same solution as before) required to neutralization it will be –

(a) 4 ML

(b) 8 ML

(c) 12 ML

(d) 16 ML

Ans: (d) 16 ML.

Reason:- 10 mL of NaOH requires 8ML HCL for neutralization

∴1 mL of NaOH requires -> 8/10 ml of HCL

∴20 ML of NaOH requires -> 8/10 x 20 ml of HCL

= 16 ML

∴20 ML NAOH requires = 16 ML of HCL

(Q4) Which of the following types of medicines is used for treating indigestion?

(a) Antibiotic

(b) Analgesic

(c) Antacid

(d) Antiseptic

Ans: (c) Antacid.

Reason:-

Antacid is base which neutralizes execs of acid in the stomach produced due to indigestion.

(Q5) Write word equations & then balanced equations for the reaction taking place when –

(a) Dilute sulphuric acid react with Zinc granules.

Ans:- Word equation:-

Zinc + Sulphuric acid -> Zinc sulphate + Hydrogen

Balanced equation:-

Zn(s) + H2 So4 (dil) ->ZnSo4 (aq) + H2 (g)

(b) Dilute hydrochloric acid reacts with magnesium ribbon.

Ans: Word equation:-

Magnesium + Hydrochloric acid -> Magnesium chloride + Hydrogen

Balanced equation:-

Mg (s) + 2HCL (dil) -> MgCl2 (aq) + H2 (g)

(c) Dilute sulphuric acid reacts with aluminum powder

Ans: Word equation

Aluminium + Sulphuric acid -> Aluminium Sulphate + hydrogen

(Q5) c. -> balanced equation:-

2 Al (s) + 3H2So4 (dil) -> Al2(So4)3 (aq) + 3H2 (g)

(d) Dilute hydrochloric acid reacts with iron fillings.

Ans: Word hydrochloric acid reacts with iron fillings.

Ans: Word equation:-

Iron + Hydrochloric acid -> Iron chloride + Hydrogen

Balanced equation:-

Fe (s) + 2HCL (dil) -> Fecl2 (aq) + H2(g)

(Q6) Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it.

Ans. Compounds such as alcohol and glucose also contain hydrogen but not categorized as acid, it can be explained by the following activity.

Procedure:-

  • Take solutions of alcohol & glucose
  • Fix the two nails on a cork & place the cork in 100 ML of beaker.
  • Connect the nails to the two terminals of a 6 volt battery through a bulb & switch as shown in the given figure.
  • Now pour alcohol in the beaker & switch on the current.
  • The bulb does not glow
  • Repeat the experiments with glucose. The bulb does not glow in this case also.

This shows that alcohol & glucose does not produces H+ ions in the solution. Hence due to absence of H+ iron alcohol & glucose are not categorised as acid.

(Q7) Why does distilled water not conduct electricity. Whereas rain water does?

Ans: Distilled water is a pure form of water. It does not contains ions, but rain water contains ions due to presence of dissolved salts in it. When rain falls on earth, rain water combines with atmospheric chemical substances which results into the formation of various dissolved salts.

Hence, distilled water not conduct electricity but rain water conduct it.

(Q8) Why acids not show acidic behaviour in the absence of water?

Ans. Acids shows their acidic behaviour due to the presence of H+ ions. Hydrogen ions (H+) can only produced in the presence of water. In the absence of water acids does not form hydrogen ions.

Hence acids not show acidic behaviour in the absence of water.

(Q9) Five solutions A, B, C, D & E when tested with universal indicators showed pH as-

4, 1, 11, 7 & 9 respectively. Which solution is –

(a) Neutral?

(b) Strongly alkaline?

(c) Strongly acidic?

(d) Weakly acidic?

(e) Weakly alkaline?

  • According to PH scale –

(a) Neutral : D with Ph = 7

(b) Strongly alkaline :- C with pH = 11

(c) Strongly acidic :- B with pH = 1

(d) Weakly alkaline :- E with pH = 9

(e) Weakly acidic :- A with pH = 4

(Q10) 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: When acid reacts with metal (Magnesium ribbon) fizzing occurs due to the production of hydrogen gas. As, hydrochloric acid is very strong acid & acetic acid is weaker acid, the fizzing occurs more vigorously in the presence of HCL.

i.e. in test tube A than test tube B.

Mg (s) + HCL (L) -> MgCl2 (L) + H2 (g) ↑

(Q11) Fresh milk has pH of 6. How do you think the pH will change as it turns into curd?

Explain your answer.

Ans: As we know, according to pH scale – pH value decreases with increasing acidic strength. Fresh milk has pH of 6. When it turns into curd it becomes more acidic. Therefore pH will deceases, with increasing acidic strength.

(Q12) 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) -> in alkaline condition, milk does not set as curd easily. Therefore a milkman shifts the pH of the fresh milk from 6 to slightly alkaline.

(b) ->By the addition of small amount of baking soda (Which is base) milk becomes slightly alkaline or basic than usual milk. Hence, acids produced to set the curd are neutralised by the base. Therefore milk take a long time to set as curd.

(Q13) Plaster of Paris should be stored in moisture proof container. Explain why?

Ans: Plaster of Paris should be stored in moisture proof contain, because plaster of Paris easily absorbs water from moisture & it changes to gypsum, a hard solid mass which makes plaster of Paris useless.

(Q14) What is neutralization reaction? Give two examples.

Ans: The reaction between an acid & a base to give a salt & water is known as neutralisation reaction.

Acid + Base -> Salt + water

Examples:-

(1) NAOH (aq) + HCL (aq) -> NACL (aq) + H2O (l)

Sodium Hydroxide Hydrogen Chloride Sodium Chloride  Water

(Base)                        (Acid)                   (Salt)

(2) KOH + HNO3-> KNO3 + H2O

Potassium Hydrooxide Nitric Acid  -> Potassium Nitrate

Base                                                   (Salt)

(Q15) Give the important uses of washing soda & baking soda.

Ans: Uses of washing soda:- (Na2Co3.10H2O)

(1) It is used in glass, soap, & paper industries.

(2) It is used in the manufacture of borax

(3) It is used for domestic purpose as a cleaning agent

(4) It is used for removing permanent hardness of water.

* Uses of baking soda:- (NaHCO3)

(1) It is used for making baking powder.

(2) It is used in soda-acid fire extinguisher.

(3) It acts as an antacids, which reduces the acidity in stomach.

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