CBSE Class 10 Science Acids Bases and Salts Assignment Set A

Read and download free pdf of CBSE Class 10 Science Acids Bases and Salts Assignment Set A. Get printable school Assignments for Class 10 Science. Class 10 students should practise questions and answers given here for Chapter 2 Acids Bases Salts Science in Class 10 which will help them to strengthen their understanding of all important topics. Students should also download free pdf of Printable Worksheets for Class 10 Science prepared as per the latest books and syllabus issued by NCERT, CBSE, KVS and do problems daily to score better marks in tests and examinations

Assignment for Class 10 Science Chapter 2 Acids Bases Salts

Class 10 Science students should refer to the following printable assignment in Pdf for Chapter 2 Acids Bases Salts in Class 10. This test paper with questions and answers for Class 10 Science will be very useful for exams and help you to score good marks

Chapter 2 Acids Bases Salts Class 10 Science Assignment

Question. An aqueous solution with pH = 1 is
(a) strongly acidic
(b) strongly basic
(c) neutral
(d) weakly acidic

Answer : A

Question. Which of the following is(are) true when HCl (g) is passed through water ?
(i) It does not ionise in the solution as it is a covalent compound.
(ii) It ionises in the solution.
(iii) It gives both hydrogen and hydroxyl ion in the solution.
(iv) It forms hydronium ion in the solution due to the combination of hydrogen ion with water molecule.
(a) (i) only
(b) (iii) only
(c) (ii) and (iv)
(d) (iii) and (iv)

Answer : C

Question. Which among the following is not a base? 
(a) NaOH
(b) KOH
(c) NH4OH
(d) C2H5OH

Answer : D

Question. What is the pH range of our body?
(a) 7.0 – 7.8
(b) 7.2 – 8.0
(c) 7.0 – 8.4
(d) 7.2 – 8.4

Answer : A

Question. During the preparation of hydrogen chloride gas on a humid day, the gas is usually passed through the guard tube containing calcium chloride. The role of calcium chloride taken in the guard tube is to 
(a) absorb the evolved gas
(b) moisten the gas
(c) absorb moisture from the gas
(d) absorb CL ions from the evolved gas

Answer : C

Question. Sodium hydroxide is used
(a) as an antacid
(b) in manufacture of soap
(c) as a cleansing agent
(d) in alkaline batteries

Answer : B

Question. Tomato is a natural source of which acid?
(a) Acetic acid
(b) Citric acid
(c) Tartaric acid
(d) Oxalic acid

Answer : D

Question. Which of the following statement is not correct? 
(a) All metal carbonates react with acid to give salt, water and carbon dioxide.
(b) All metal oxides react with water to give salt and acid.
(c) Some metals react with acids to give salt and hydrogen.
(d) Some non-metal oxides react with water to form an acid.

Answer : B

Question. How many water molecules does hydrated cal-cium sulphate contain?
(a) 5
(b) 10
(c) 7
(d) 2

Answer : D

Question. Which of the following phenomena occur, when a small amount of acid is added to water ?
(i) Ionisation
(ii) Neutralisation
(iii) Dilution
(iv) Formation
Choose the correct option from the following:
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (ii) and (iv)

Answer : C

Question. Which of the following salts does not contain water of crystallisation?
(a) Blue vitriol
(b) Baking soda
(c) Washing soda
(d) Gypsum

Answer : B

Question. At what temperature is gypsum heated to form Plaster of Paris?
(a) 90°C
(b) 100°C
(c) 110°C
(d) 120°C

Answer : B

Question. Which of the following is used for dissolution of gold ? 
(a) Hydrochloric acid
(b) Sulphuric acid
(c) Nitric acid
(d) Aqua regia

Answer : D

Question. NaOH is obtained by electrolysis of
(a) Aq. solution of NaCl
(b) Aq. Na2CO3
(c) Aq. NaHCO3
(d) Molten NaCl

Answer : A

Question. Equal volumes of hydrochloric acid and sodium hydroxide solutions of same concentration are mixed and the pH of the resulting solution is checked with a pH paper. What would be the colour obtained?
(a) Red
(b) Yellow
(c) Yellowish green
(d) Blue

Answer : C

Question. Which of the following are present in a dilute aqueous solution of hydrochloric acid? 
(a) H3O+ + Cl
(b) H3O+ + OH
(c) Cl + OH
(d) unionised HCl

Answer : A

Question. Which one of the following can be used as an acid-base indicator by a visually impared (blind) student ?
(a) Litmus
(b) Turmeric
(c) Vanilla essence
(d) Petunia leaves

Answer : C

Question. NaHCO, formed by reaction of
(a) NaOH + H2CO3
(b) NaCl + H2CO3
(c) Na2CO3 + HCl
(d) NaOH + Na2CO3

Answer : A

Question. Which of the following statements is true for acids?
(a) Bitter and change red litmus to blue.
(b) Sour and change red litmus to blue.
(c) Sour and change blue litmus to red.
(d) Bitter and change blue litmus to red.

Answer : C

Question. An aqueous solution turns red litmus solution blue. Excess addition of which of the following solution would reverse the change? 
(a) Baking power
(b) Lime
(c) Ammonium hydroxide solution
(d) Hydrochloric acid

Answer : D

Question. pH of H20 is
(a) 7
(b) 8
(c) 9
(d) 10

Answer : A

Question. Ag2S reacts with H2SO4 to form
(a) AgSO4
(b) Ag2SO4 + H2S
(c)Ag2O + H2S
(d) AgOH + H2S

Answer : B

Question. Lime water reacts with chlorine to form
(a) CaCl2
(b) CaOCl2
(c) Ca(ClO3)2
(d) CaO2Cl2

Answer : B

Question. In an attempt to demonstrate electrical conductivity through an electrolyte, the following apparatus was set up.
Which among the following statement)s) is (are) correct?
(i) Bulb will not glow because electrolyte is not acidic.
(ii) Bulb will glow because NaOH is a strong base and furnishes ions for conduction.
(iii) Bulb will not glow because circuit is incomplete.
(iv) Bulb will not glow because it depends upon the type of electrolytic solution.
(a) (i) and (iii)
(b) (ii) and (iv)
(c) (ii) only
(d) (iv) only

Answer : C

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

Question : Common salt, besides used in kitchen, can also be used as the raw material for making:
i) Washing soda ii) bleaching powder iii) Baking soda iv) slaked lime
(a) i) and ii) 
(b) i) and iii)
(c) i), ii) and iii)
(d) i),iii) and iv)

Answer : C

Question : Under what soil condition do you think a farmer would spread or treat the soil of his fields with quick lime (CaO) or slaked time (CaCO3)?
(a) When the pH of the soil increases
(b) When the nutrients of the soil is lost
(c) When the pH of the soil decreases
(d) All of these
 
Answer : C
Explanation: When the pH of the soil becomes acidic, slaked lime or quick lime is added to neutralise the soil.

Question : The pH of gastric juices released during digestion is:
(a) less than 7
(b) more than 7
(c) Equal to 7
(d) equal to 0

Answer :  A

Question : Which of the following salts does not contain water of crystallization?
(a) Blue vitriol
(b) Baking soda
(c) Gypsum
(d) Washing soda

Answer : B

Question : Electrolysis of brine solution produces chlorine gas and hydrogen at 
(a) Anode and cathode, respectively.
(b) Both at cathode
(c) Cathode and anode respectively
(d) Both at Anode
 
Answer : A
Explanation: On electrolysis, brine (sodium chloride solution) produces hydrogen gas at the cathode and chlorine gas at the anode.
The half-equations for the reactions are:
At the cathode: 2 H+(aq) + 2 e → H2(g)
At the anode: 2 Cl(aq);→ Cl2(g) + 2 e
Overall process: 2 NaCl (or KCl) + 2 H2O → Cl2 + H2 + 2 NaOH (or KOH)
The solution left provides sodium hydroxide (a strong alkali).
 
Question : Which one of the following is not required to find the pH of a solution? 
(a) Litmus paper
(b) Standard pH value chart
(c) pH paper
(d) Universal indicator
 
Answer : A
Explanation: Litmus paper cannot be used to find the pH of a solution.
 
Question :  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
 
Question : Which one of the following is not required to find the pH of a solution? 
(a) Litmus paper
(b) Standard pH value chart
(c) pH paper
(d) Universal indicator
 
Answer : A
Explanation: Litmus paper cannot be used to find the pH of a solution.
 
Question :  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 of HCl solution (the same solution as before) required to neutralise it will be
(a) 4 mL
(b) 8mL
(c) 12 mL
(d) 16 mL
 
Answer : D
 
Question :  Which one of the following types of medicines is used for treating indigestion?
(a) Antibiotic
(b) Analgesic
(c) Antacid
(d) Antiseptic
 
Answer : C
 
Question : Under what soil condition do you think a farmer would spread or treat the soil of his fields with quick lime (CaO) or slaked time (CaCo3)? 
(a) When the pH of the soil increases
(b) When the nutrients of the soil is lost
(c) When the pH of the soil decreases
(d) All of these
 
Answer : C
Explanation: When the pH of the soil becomes acidic, slaked lime or quick lime is added to neutralise the soil.
 

(a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
(b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.
(c) Assertion is true but the Reason is false.
(d) The statement of the Assertion is false but the Reason is true.

Question. Assertion: Ammonium hydroxide is Weak Base
Reason: Phenolphthalein becomes pink in NH2OH

Answer : B

Question. Assertion: Bleaching power liberate chlorine when kept in atmosphere.
Reason: CaOCl2 reacts with CO2 present in atmosphere to form CaCO3 and chlorine gas.

Answer : A

Question. Assertion: Universal indicator gives green colour with distilled water.
Reason: pH of distilled water is 7 and it is neutral and universal indicator gives green colour with neutral solution.

Answer : A

Question. Assertion: Carbonic acid is weak acid
Reason: It ionised completely in aqueous solution.

Answer : C

Question. Assertion: Copper sulphate is acidic salt.
Reason: It is a salt of weak base [Cu(OH)7] and strong acid (H7SO4).

Answer : A

 

Important Questions for NCERT Class 10 Science Acids Bases and Salts

 
Very Short Questions :

Question. What is the colour of methyl orange in NaOH?
Answer: Yellow.

Question. A bud of petunia became reddish purple after first shower of rain. What does it indicate?
Answer: The rain was acid-rain.

Question. How will you test a gas which is liberated when HCl acid reacts with an active metal? 
Answer: The gas liberated is hydrogen gas. If we bring a burning splinter near the test tube, the splinter will extinguish with a pop sound.

Question. What is the colour of phenolphthalein in milk of magnesia?
Answer: Pink.

Question. What will happen to blue litmus when it is added to soda water?
Answer: It changes to red.

Question. What are indicators?
Answer: Those substances which change their colour in different types of substances are called indicators.

Question. What would be the colour of litmus in a solution of sodium carbonate?
Answer: The red litmus will change to blue in sodium carbonate solution.

Question. Name a salt which does not contain water of crystallisation.
Answer: Salts like barium sulphate, potassium chloride, sodium nitrate, etc does not contain water of crystallisation.

Question. Dry ammonia gas has no action on litmus paper, but a solution of ammonia in water turns red litmus paper blue. Why is it so?
Answer: Ammonia dissolves in water, forms ammonium hydroxide which is base and turns red litmus blue.
NH3 + H2O → NH4+ + OH
Dry ammonia gas does not change into OH ions.

Question. Name an acid-base indicator prepared at home.
Answer: Beetroot extract.

 

Short Questions :

 
Question : Write some uses of caustic soda? 
Answer : Three uses of caustic soda:
a. It is used in paper industry.
b. It is used in manufacture of soap and detergents.
c. It is used in the manufacture of artificial fibres.
d. It is used as a cleansing agent and in the manufacturing of washing soda.
e. Sometimes, sodium hydroxide is also used as a reagent in the laboratories.
f. It is used in the preparation of soda lime.
g. It is used in the extraction of aluminium by purifying bauxite.
 
Question :  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) Sulphuric acid + Zinc → Zinc sulphate + Hydrogen
                  H2SO4 + Zn → ZnSO4 + H2
b) Hydrochloric acid + Magnesium → Magnesium chloride + Hydrogen
                  2HCl + Mg → MgCl2 + H2
c) Sulphuric acid + Aluminium → Aluminium sulphate + Hydrogen
                 3H2SO4 + 2Al → Al2(SO4)3 + 3H2
d) Hydrochloric acid + Iron → Iron (II) chloride + Hydrogen
                 HCl + Fe → FeCl2 + H2
 
Question : Why acids are not stored in metal containers? 
Answer : Acids cannot be stored in metal containers as they will react with the metal, forming metal salt and liberating Hydrogen gas. Containers made of glass are ideal for storage of acid due to its chemical inertness.
 
Question :  Compounds such as alcohols and glucose also contain hydrogen but are not categorized as acids. Describe an activity to prove it.
Answer :   Because alcohols and glucose do not dissociate into hydrogen ions, hence these cannot be categorized as acids.
Activity- Make a circuit as shown in figure. When we pour HCl in beaker then bulb glows, but when we pour alcohol or glucose solution in beaker then bulb do not glow. This is because of absence of ions in alcohol and glucose solutions.

8th.sci.eng.oct.nov.21.22 12

 

Question : What is baking powder? How does it make the cake soft and spongy?
Answer :  Baking powder is a mixture of sodium hydrogen carbonate and tartaric acid On heating it liberates COwhich makes the cake soft and spongy

Question : Write the chemical name and formula of the compound which is used as an antacid.
Answer :  Sodium bicarbonate, NaHCO3 

Question :  a) A milk man adds a very small amount of baking soda to fresh milk. Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
b) Mention pH range within which our bodyworks?
c) Explain how antacids give relief from acidity.
d) Mention the nature of tooth pastes. How do they prevent tooth decay?
Answer :  a) It is done to prevent the formation of lactic acid which spoils the milk
b) pH range 7.0- 7.8
c) Antacids neutralizes excess of acid in our body and gives relief.
d) Basic) Neutralize the acid formed in the mouth

 
Question : Although acetic acid is highly soluble in water but still it is a weak acid. Explain why? 
Answer : The strength of an acid depends upon the extent of ionization. Acetic acid is highly soluble in water but it dissociates partially in the aqueous solution to produce a small amount of H+ ions and, therefore, considered as a weak acid.
 

Question : A gas X reacts with lime water and forms a compound Y which is used as bleaching agent in the chemical industry. Identify X and Y. Give the chemical equation of the reaction involved)
Answer :  X is chlorine Y is CaOCl2 (calcium oxy chloride) used as bleaching agent.
        Ca (OH)2+ Cl2—–→ CaOCl2 +H2O 

 
Question : Electrolysis of brine solution produces chlorine gas and hydrogen at 
a) Anode and cathode, respectively.
b) Both at cathode
c) Cathode and anode respectively
d) Both at Anode
Answer : A
Explanation: On electrolysis, brine (sodium chloride solution) produces hydrogen gas at the cathode and chlorine gas at the anode.
The half-equations for the reactions are:
At the cathode: 2 H+(aq) + 2 e → H2(g)
At the anode: 2 Cl(aq);→ Cl2(g) + 2 e
Overall process: 2 NaCl (or KCl) + 2 H2O → Cl2 + H2 + 2 NaOH (or KOH)
The solution left provides sodium hydroxide (a strong alkali).
 
Question : Plaster of Paris should be stored in a moisture-proof container. Explain why? 
Answer :  Plaster of Paris should be stored in a moisture-proof container, because in presence of moisture, plaster of paris sets to give a hard mass.
a-15
It can be no longer used for making moulds and statues. To avoid above reaction to occur Plaster of Paris be stored in moisture- proof containers.
 
 
Question : An aqueous solution turns red litmus solution blue. Excess addition of which solution would reverse the change? 
Answer : Changing of red litmus to blue indicates that the solution is basic. So to neutralise the basic solution an acid should be added. To revert the colour change that is to change blue litmus red, excess of acid needs to be added so that the solution becomes acidic. 
 
 
Question : Give important properties of bases (alkalies). 
Answer : i. Bases are soapy to touch and have bitter taste.
ii. They change the colour of indicators.
 a-9
iii. They act as electrolytes.
iv. They have a corrosive action on the skin.
v. Action with ammonium salts : When they are warmed with an ammonium salt, ammonia gas is produced.
e.g. NH4Cl + NaOH → NaCl + H2O + NH3
vi. They absorb carbon dioxide from the air to form carbonates.
2NaOH + CO2 → Na2CO3 + H2 O
2KOH + CO2 → K2CO3 + H2O
vii. They neutralise acids to from salt and water
Ca(OH)2 + 2HCl → CaCl2 + 2H2 O
Fe(OH)2 + 2HCl → FeCl2 + 2H2 O
viii. Action of heat : All bases except NaOH decompose on heating to give oxides.
a-10
 
ix. Precipitation reactions : When added to the solutions of the salts of the heavy metals viz. copper, iron, zinc, etc. the bases produce insoluble metal hydroxides as precipitates.
CuSO4(aq) + 2NH4OH → (NH4)2SO4 + Cu(OH)2↓ (pale blue)
ZnSO4(aq) + 2NaOH(aq) → Na2SO4(aq) + Zn(OH)2 ↓ (white)
x. Amphoteric nature : The hydroxides of zinc, aluminium and lead are amphoteric
i.e. they can act as weak bases as well as weak acids.
a. As weak bases :
Zn(OH)2 + 2HCl (dil) → ZnCl2(aq) + 2H2O
Al(OH3)(s) + 3HCl(dil) → AlCl3(aq) + 3H2O
b. As weak acids
 
a-11
 
Question : What will happen if water is added to an acid or a base? 
Answer :  If water is added to an acid or base a large amount of heat energy is evolved which may cause the reaction mixture to splash out and cause injury to the person.
 
Question : Two solutions P and Q have pH 2 and 12. Which solution has more concentration of H+ (aq) ions ? 
Answer : The pH value of a solution varies from 0 to 14. The pH value is 0 for a very strong acid and the pH value is 14 for a very strong base. The pH value is 7 for a neutral solution.
Hence P is acidic and Q is basic in nature. The concentration of hydrogen ion decreases from pH value of 0 to 14 therefore P has more hydrogen ion concentration.
 
Question :How can CuSO4 be used for detecting the presence of water ? 
Answer :  Anhydrous copper sulphate(CuSO4) is white in colour but turns blue when comes in contact with water to form CuSO4. 5H2O. Thus, it can be used to detect the presence of moisture.
 
 
Question : How is plaster of Paris prepared ? Why is temperature control necessary during its preparation ? How does it react with water ? 
Answer : Plaster of paris is prepared from gypsum.
Gypsum is calcium sulphate dihydrate. The chemical formula of gypsum is CaSO4·2H2O
Plaster of paris is prepared by heating gypsum to a temperature of 373K.When gypsum is heated to a temperature of 373k ,It loses three-Fourths of its water of crystallisation and forms plaster of paris.
a-14 
It may be noted the temperature should be controlled carefully. It should not be allowed to rise above 425 K, because the whole of water is lost and anhydrous calcium sulphate (CaSO4) is produced. It is called dead burnt plaster. It has not such property as that of plaster of paris.
When mixed with water, it forms a paste which sets into a hard mass. This is called setting of Plaster of Paris. The setting of Plaster of Paris is due to its hydration into gypsum.
(CaSO4)2.H2O + 3H2O → CaSO4.2H2O
Plaster of paris Gypsum

Question : Which of the following is a double salt ? 
(A) Blue Vitriol
(B) Glauber’s salt
(C) Potash Alum
(D) Potassium Ferrocyanide
Answer : C

Question : The reagent obtained by dissolving Copper sulphate in aqueous solution of Citric acid and Sodium carbonate is...................
(A) Bayer’s reagent
(B) Tollen’s reagent
(C) Fehling reagent
(D) Benedict reagent
Answer : D

Question : When Sodium carbonate (Na2CO3) reacts with Silica (SiO2) gives.................
(A) Soda Glass
(B) Water glass
(C) Crook’s glass
(D) Pyrex glass
Answer : B

Question : In order to decrease the role of setting of Cement, which compound is mixed in it ?
(A) Ca(OH)2 (Slaked lime)
(B) CaCO3 (Calcium Carbonate)
(C) CaSO4.2H2O (Gypsum)
(D) Al2O3 (Alumina)
Answer : C

Question : Which one of the following is not base ? 
(A) B(OH)3
(B) KOH
(C) Ca(OH)2
(D) NH4OH
Answer : A

Question : The nature of solution when sodium carbonate is dissolved in water will be
(A) acidic
(B) basic
(C) neutral
(D) amphoteric
Answer : B

Question : pH of a solution is zero. The nature of this solution is 
(A) acidic
(B) basic
(C) neutral
(D) amphoteric
Answer : A

Question : The difference in number of crystalline water molecules in a molecule of gypsum and a molecule of plaster of Paris is 
(A) 5/2
(B) 2
(C) 1/2
(D) 3/2
Answer : D

Question : Match the following : 
(a) formic acid            (i) dehydrating agent
(b) Nitric acid             (ii) organic acid
(c) Electrolyte            (iii) Mineral acid
(d) Conc. H2SO4        (iv) Nacl
(A) (a) (ii), (b) (iii), (c) (iv), (d) (i)
(B) (a) (i), (b)(ii), (c) (iii), (d) (iv)
(C) (a) (iii), (b)(i), (c) (iv), (d) (ii)
(D) (a) (iv), (b)(iii), (c) (i), (d) (ii)
Answer : A

Question : A milkman added a small pinch of baking soda of fresh milk which has pH close to 6. As a result, pH of the medium
(A) became close to 2
(B) became close to 4
(C) did not undergo any changes
(D) became close to 8
Answer : D

Question : Which of the following salts does not contain any water of crystallisation ?
(A) blue vitriol
(B) washing soda
(C) baking Soda
(D) gypsum
Answer : C

Question : The substance which is chemically resistant and can hold aqua regia
(A) Ceramics
(B) Glass
(C) Fibre
(D) Thermosetting plastic
Answer : B

Question : Skin becomes yellow in conc. HNO3 as 
(A) HNO3 acts as an oxidizing agent
(B) HNO2 acts as a dehydrating agent
(C) Nitro-cellulose is formed
(D) The proteins are converted into xantho proteins
Answer : A

Question : Match the items of column I with the items of column II 
Column – I (Polymers)       Column – II
a. aq. NaCl solution           i. Acidic
b. aq. Na2CO3 solution     ii. Basic
c. aq. NH4Cl solution        iii. Neutral
d. aq. CaO solution           iv. Amphoteric
(A) c-i, d-iii, b-ii, a-i
(B) d-i, b-iv, a-iii c-iv
(C) a-iii, b-ii, c-i, d-iii
(D) b-ii, a-iii, d-ii, c-i
Answer : D

Question : The pH of pure water at 25°C is 7. If water is heated to boil, then 
(A) pH will decrease and water will become acidic
(B) pH will increase and water will become basic
(C) pH will decrease but water will remain natural
(D) pH will remain 7
Answer : C

Question : Which of the following is pH of basic solution ?
(A) 7
(B) 4.2
(C) 6.9
(D) 10.2
Answer : B

Question : Which reagent is able to dissolve gold and platinum ? 
(A) Nitric acid
(B) Aqua-regia
(C) Hydrochloric acid
(D) Sulphuric acid.
Answer : B

Question : The conjugate base of H2PO4 is : 
(A) PO43–
(B) P2O5
(C) H3PO4
(D) HPO42–
Answer : D

Question : What is the conjugate base of OH ? 
(A) O2
(B) H2O
(C) O
(D) O2–
Answer : D

Question : Hydrogen ion concentration in mol/L in a solution of pH = 5.4 will be :
(A) 3.98 × 108
(B) 3.88 × 106
(C) 3.68 × 10–6
(D) 3.98 × 10–6
Answer : D

Question :Three reactions involving H2PO4 are given below :
(i) H3PO4 + H2O → H3O+ + H2PO4
(ii) H2PO4 + H2O →  HPO42– + H3O+
(iii) H2PO4 + OH– →  H3PO4+ O2–
In which of the above, does H2PO4 act as an acid ?
(A) (ii) only
(B) (i) and (ii)
(C) (iii) only
(D) (i) only
Answer : A

Question : How many litres of water must be added to 1 litre an aqueous solution of HCl with a pH of 1 to create an aqueous solution with pH of 2 ? 
(A) 0.1 L
(B) 0.9 L
(C) 2.0 L
(D) 9.0 L
Answer : D

Question : The substance not likely to contain CaCO3 is : 
(A) calcined gypsum
(B) sea shells
(C) dolomite
(D) a marble statue
Answer : A

Question : Tooth pastes are generally 
a. natural
b. acidic
c. basic
d. neutral
Answer : C
Explanation: Toothpastes are generally basic because their function is to react with the excess acid in our mouth and thus prevent tooth decay. 

Question : 10 mL of a solution of NaOH is found to be completely neutralized by 8 mL of a given solution of HCl. If we take 20 mL of same solution of NaOH, the amount of HCl solution required to neutralize it will be 
a. 12 mL
b. 16 mL
c. 8 mL
d. 4 mL
Answer : B
Explanation: 10 mL of NaOH neutralises 8mL of HCl
i.e. 1 mL of NaOH neutralises 8/10 mL of HCl
so, 20 mL of NaOH will neutralise  8/10 X 20= 16mL of HCl
 
Question : Which of the following gives CO2 on heating? 
a. Quick lime
b. Limestone
c. Slaked lime
d. Soda ash
Answer : B
Explanation: Limestone (CaCO3) decomposes on heating to produce quicklime (CaO) and CO2 gas.
 
Question : A group of students, while on excursion trip is campaigning on the hills. One morning, they find themselves engulfed in a thick blanket of snow. One of the senior member of the group suggests to sprinkle common salt on the ice slit covering the pavement. Now answer the following questions: 
i. What is the purpose of sprinkling common salt on ice slit?
ii. Can we use any other substance in place of common salt?
iii. What values are associated with the students?
Answer : i. Sprinkling common salt on icy roads, ice/snow lowers the freezing point of ice due to which the ice or snow melts down. The softened ice/snow can be easily cleared from the roads.
ii. Calcium chloride can be used in place of common salt. It can lower the freezing point up to -55°C.
iii. The students are caring, helping, have supporting nature and have scientific knowledge.
 
 
Question : Write the chemical name and formula of baking soda. 
Answer : The chemical name of baking soda is sodium hydrogen carbonate.
The formula of baking soda is NaHCO3.
 
Question : What is pH paper ? 
Answer : A filter paper soaked in universal indicator and then dried is called pH paper. 
 
 
Question : A road tanker carrying an acid was involved in an accident and its contents spilled on the road. At the side of the road iron drain cover began melting and fizzing as the acid ran over them. A specialist was called to see if the acid actually leaked into the nearby river. 
(a) Explain why specialist could carry out sample test to see of the river water contains some acid or not
(b) Suggest a better report name for the word 'melting'
(c) Explain why the drain covers began fizzing as the acid ran over them.
Answer : 1. It can be done by adding a strip of blue litmus paper into a tube containing a small amount of sample water if the colour changes into red, this means that some acid has gone into the river.
2. The acid has reacted chemically with the drain cover which is usually made of iron. The correct word is corrosion.
3. Iron reacts with an acid (H2SO4
OR HCl) to evolve H2 gas. Since the gas is released immediately accompanied by large number of bubbles Fizzing of detain covers is expected.
 
Question : In the following schematic diagram for the preparation of hydrogen gas as shown in the figure, what would happen if the following changes are made?
a-13
i. In place of zinc granules, same amount of zinc dust in taken in the test tube.
ii. Instead of dilute sulphuric acid, dilute hydrochloric acid is taken.
iii. In place of zinc, copper turnings are taken.
iv. Sodium hydroxide is taken in place of dilute sulphuric acid and the test tube is heated. 
Answer : i. Since the zinc dust has a larger surface area than zinc granules. If the same amount of zinc dust is taken in the test tube then the reaction will be comparatively faster and hydrogen gas will evolve with greater speed.
ii. With dilute hydrochloric acid, almost the same amount of gas is evolved.
iii. With copper turnings, hydrogen gas will not evolve because copper is less reactive and it will not displace hydrogen from the acid. Hence, no reaction will take place.
iv. Zinc also reacts with NaOH. So, if sodium hydroxide is taken, then hydrogen gas will be evolved.
 
a-12
Chapter 01 Chemical Reactions and Equations
CBSE Class 10 Science Chemical Reactions and Equations Assignment

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