Science Ncert Exemplar Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations are provided here with simple step-by-step explanations. These solutions for Chemical Reactions And Equations are extremely popular among Class 10 students for Science Chemical Reactions And Equations Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Science Ncert Exemplar Book of Class 10 Science Chapter 1 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Science Ncert Exemplar Solutions. All Science Ncert Exemplar Solutions for class Class 10 Science are prepared by experts and are 100% accurate.

Page No 1:

Question 1:

Which of the following is not a physical change?
(a) Boiling of water to give water vapour
(b) Melting of ice to give water
(c) Dissolution of salt in water
(d) Combustion of Liquefied Petroleum Gas (LPG)

Answer:

Boiling of water to give water vapour, melting of ice to give water and dissolution of salt in water are all examples of physical change, as in any of the three processes there is only change in state and the chemical composition of the compound is not changing. Whereas when liquified petroleum gas is burnt in air, it is actually undergoing a chemical reaction with oxygen gas present in the air and as a result of which two new products water and carbon dioxide are formed. Therefore, option D is an example of chemical change.

​Hence, the correct answer is option D.

Page No 1:

Question 2:

The following reaction is an example of a 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g)
(i) displacement reaction
(ii) combination reaction
(iii) redox reaction
(iv) neutralisation reaction
(a) (i) and (iv)
(b) (ii) and (iii)
(c) (i) and (iii)
(d) (iii) and (iv)

Answer:

In the following reaction, 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g)
Hydrogen is getting displaced from NH3 by O2 to form NO hence, this is an example of a displacement reaction. At the same time, the addition of oxygen to a compound is called oxidation So, NHis getting oxidised to NO. Addition of hydrogen to a compound is called reduction so, Ois reduced to H2O. Since both, the process of oxidation and reduction are happening at the same time this reaction is also an example of a redox reaction.  

Hence, the correct answer is option C.

Page No 1:

Question 3:

Which of the following statements about the given reaction are correct?
3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)
(i) Iron metal is getting oxidised
(ii) Water is getting reduced
(iii) Water is acting as reducing agent
(iv) Water is acting as oxidising agent
(a) (i), (ii) and (iii)
(b) (iii) and (iv)
(c) (i), (ii) and (iv)
(d) (ii) and (iv)

Answer:

In the following reaction, 3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)
As the addition of oxygen is called oxidation and removal of oxygen is known as reduction so, Fe is getting oxidised to Fe3O4 , at the same time H2O is getting reduced to H2.
In a redox reaction, the reactant causing the oxidation of other reactant is called as an oxidising agent since H2O is causing the oxidation of Fe, therefore H2O is the oxidising agent.

Hence, the correct answer is option C.

Page No 1:

Question 4:

Which of the following are exothermic processes?
(i) Reaction of water with quick lime
(ii) Dilution of an acid
(iii) Evaporation of water
(iv) Sublimation of camphor (crystals)
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (iii) and (iv)

Answer:

When water is added to quick lime, they react vigorously to form lime water and an excess amount of heat is lost to the surrounding. In the same way reaction of an acid with water is also an example of a highly exothermic reaction. Whereas evaporation of water and sublimation of camphor both these process requires heat for them to proceed in the forward direction and hence are examples of endothermic reactions.

Hence, the correct answer is option A.



Page No 2:

Question 5:

Three beakers labelled as A, B and C each containing 25 mL of water were taken. A small amount of NaOH, anhydrous CuSO4 and NaCl were added to the beakers A, B and C respectively. It was observed that there was an increase in the temperature of the solutions contained in beakers A and B, whereas in case of beaker C, the temperature of the solution falls. Which one of the following statement(s) is(are) correct?
(i) In beakers A and B, exothermic process has occurred.
(ii) In beakers A and B, endothermic process has occurred.
(iii) In beaker C exothermic process has occurred.
(iv) In beaker C endothermic process has occurred.
(a) (i) only
(b) (ii) only
(c) (i) and (iv)
(d) (ii) and (iii)

Answer:

Dissolution of NaOH and CuSO4 in water are examples of the exothermic process in which the temperature of the solution increases. Whereas, dissolution of NaCl in water is an example endothermic process in which the temperature of the solution decreases.

Hence, the correct answer is option C.

Page No 2:

Question 6:

A dilute ferrous sulphate solution was gradually added to the beaker containing acidified permanganate solution. The light purple colour of the solution fades and finally disappears. Which of the following is the correct explanation for the observation?
(a) KMnO4 is an oxidising agent, it oxidises FeSO4
(b) FeSO4 acts as an oxidising agent and oxidises KMnO4
(c) The colour disappears due to dilution; no reaction is involved
(d) KMnO4 is an unstable compound and decomposes in presence of FeSO4 to a colourless compound.

Answer:

When a dilute ferrous sulphate solution was gradually added to the beaker containing acidified permanganate solution, acidified permanganate gets reduced to MnSOand ferrous sulphate gets oxidised to Fe2(SO4)3 due to which the light purple colour of the solution fades and finally disappears.

Hence, the correct answer is option A.

Page No 2:

Question 7:

Which among the following is(are) double displacement reaction(s)?
(i) Pb + CuCl2 → PbCl2 + Cu
(ii) Na2SO4 + BaCl2 → BaSO4 + 2NaCl
(iii) C + O2 → CO2
(iv) CH4 + 2O2 → CO2 + 2H2O
(a) (i) and (iv)
(b) (ii) only
(c) (i) and (ii)
(d) (iii) and (iv)

Answer:

Double displacement reaction is a type of chemical reaction in which two compounds react by an exchange of ions to form two new compounds. Out of all the given options, only in option no (ii), there is a mutual exchange of ions is happening.

Hence, the correct answer is option B.

Page No 2:

Question 8:

Which among the following statement(s) is(are) true? Exposure of silver chloride to sunlight for a long duration turns grey due to
(i) the formation of silver by decomposition of silver chloride
(ii) sublimation of silver chloride
(iii) decomposition of chlorine gas from silver chloride
(iv) oxidation of silver chloride
(a) (i) only
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (iv) only

Answer:

Silver chloride on exposure to sunlight for long-duration undergo photochemical decomposition reaction to form silver metal and chlorine gas is evolved. The silver metal that is formed in the reaction is grey in colour.
2AgCl(s) →2Ag(s) + Cl2(g)

Hence, the correct answer is option A.



Page No 3:

Question 9:

Solid calcium oxide reacts vigorously with water to form calcium hydroxide accompanied by liberation of heat. This process is called slaking of lime. Calcium hydroxide dissolves in water to form its solution called lime water. Which among the following is (are) true about slaking of lime and the solution formed?
(i) It is an endothermic reaction
(ii) It is an exothermic reaction
(iii) The pH of the resulting solution will be more than seven
(iv) The pH of the resulting solution will be less than seven
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (iii) and (iv)

Answer:

When in any chemical reaction heat is liberated from the system to the surrounding, the type of reaction is called an exothermic reaction. And as calcium hydroxide is a strong base so, the pH of the resulting solution would certainly be greater than 7.

Hence, the correct answer is option B.

Page No 3:

Question 10:

Barium chloride on reacting with ammonium sulphate forms barium sulphate and ammonium chloride. Which of the following correctly represents the type of the reaction involved?
(i) Displacement reaction
(ii) Precipitation reaction
(iii) Combination reaction
(iv) Double displacement reaction
(a) (i) only
(b) (ii) only
(c) (iv) only
(d) (ii) and (iv)

Answer:

In the following chemical reaction, (NH4)2SO4(aq)+ BaCl2(aq)  BaSO4(s) + 2NH4Cl(aq) a solid insoluble precipitate is formed in the product side. At the same time, there is a mutual exchange of ions is also occurs in the rection so, it is also a double displacement reaction.

Hence, the correct answer is option D.

Page No 3:

Question 11:

Electrolysis of water is a decomposition reaction. The mole ratio of hydrogen and oxygen gases liberated during electrolysis of water is
(a) 1:1
(b) 2:1
(c) 4:1
(d) 1:2

Answer:

The decomposition of water occurs with the application of electricity in the process of electrolysis to form hydrogen and oxygen gases in the ratio 2:1 by volume.
2H2O(l) 2H2(g) + O2(g)

Hence, the correct answer is option B.

Page No 3:

Question 12:

Which of the following is(are) an endothermic process(es)?
(i) Dilution of sulphuric acid
(ii) Sublimation of dry ice
(iii) Condensation of water vapours
(iv) Evaporation of water
(a) (i) and (iii)
(b) (ii) only
(c) (iii) only
(d) (ii) and (iv)

Answer:

The endothermic process is any process in which energy in the form of heat is absorbed by the system from the surrounding for the chemical reaction to move in the forward direction.
Out of the given options, sublimation of dry ice and evaporation of water into vapour both require some minimum amount of energy to be absorbed from the surrounding for the process to occur.

Hence, the correct answer is option D.

Page No 3:

Question 13:

In the double displacement reaction between aqueous potassium iodide and aqueous lead nitrate, a yellow precipitate of lead iodide is formed. While performing the activity if lead nitrate is not available, which of the following can be used in place of lead nitrate?
(a) Lead sulphate (insoluble)
(b) Lead acetate
(c) Ammonium nitrate
(d) Potassium sulphate

Answer:

Lead sulphate is insoluble so, it will not form an aqueous solution. Lead acetate which contains Pb2+ ion can be taken for the reaction in the unavailability of aqueous lead nitrate and will be getting the same yellow precipitate of lead iodide. The reaction that follows with lead acetate would be: 
2KI(aq) + (CH3COO)2Pb(aq)  2CH3COOK(aq) + Pb(I)2(s)

Hence, the correct answer is option B.



Page No 4:

Question 14:

Which of the following gases can be used for storage of fresh sample of an oil for a long time?
(a) Carbon dioxide or oxygen
(b) Nitrogen or oxygen
(c) Carbon dioxide or helium
(d) Helium or nitrogen

Answer:

A fresh sample of oil is stored in an airtight container or is usually flushed with a non-reactive stable gas to prevent the process fo rancidity. Out of all the give options, only option D contains helium and nitrogen both of which are stable and non-reactive under standard conditions.

Hence, the correct answer is option D.

Page No 4:

Question 15:

The following reaction is used for the preparation of oxygen gas in the laboratory

2KClO3 sCatalystHeat2KCl s + 3O2 g

Which of the following statement(s) is(are) correct about the reaction?
(a) It is a decomposition reaction and endothermic in nature
(b) It is a combination reaction
(c) It is a decomposition reaction and accompanied by release of heat
(d) It is a photochemical decomposition reaction and exothermic in nature

Answer:

According to the representation of the chemical equation of the reaction, Heat is written above the arrow which means that heat is supplied to the reaction for it to proceed in the forward direction so, it is an endothermic process. At the same time since a single compound is broken into two products, this reaction could be categorised as a decomposition reaction.

Hence, the correct answer is option A. 

Page No 4:

Question 16:

Which one of the following processes involve chemical reactions?
(a) Storing of oxygen gas under pressure in a gas cylinder
(b) Liquefaction of air
(c) Keeping petrol in a china dish in the open
(d) Heating copper wire in presence of air at high temperature

Answer:

Out of all the given options, A, B and C represent physical change as all the three processes involve a change in the physical state so, no chemical reaction is involved. In option D, when a copper wire is heated to high temperature in the presence of air, it reacts with the oxygen gas present in the air to form copper oxide which involves a chemical reaction.
2Cu + O2  2CuO

Hence, the correct answer is option D.
 

Page No 4:

Question 17:

In which of the following chemical equations, the abbreviations represent the correct states of the reactants and products involved at reaction temperature?
(a) 2H2(l) + O2(l) → 2H2O(g)
(b) 2H2(g) + O2(l) → 2H2O(l)
(c) 2H2(g) + O2(g) → 2H2O(l)
(d) 2H2(g) + O2(g) → 2H2O(g)

Answer:

Combustion of hydrogen in atmospheric air is an exothermic process resulting in the production of water in the form of vapour and energy being released into the surrounding.

Hence, the correct answer is option D.

Page No 4:

Question 18:

Which of the following are combination reactions?
(i) 2KClO3 Heat 2KCl+3O2
(ii) MgO + H2O → Mg(OH)2
(iii) 4Al + 3O2 → 2Al2 O3
(iv) Zn + FeSO4 → ZnSO4 + Fe
(a) (i) and (iii)
(b) (iii) and (iv)
(c) (ii) and (iv)
(d) (ii) and (iii)

Answer:

Combination reaction is a chemical reaction in which two or more substances combine to form a single substance under suitable conditions. Out of the given options only options ii and iii represents a chemical combination reaction.

Hence, the correct answer is option D.



Page No 5:

Question 19:

Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
(a) Nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773K to form ammonia gas.
(b) Sodium hydroxide solution is treated with acetic acid to form sodium acetate and water.
(c) Ethanol is warmed with ethanoic acid to form ethyl acetate in the presence of concentrated H2SO4 .
(d) Ethene is burnt in the presence of oxygen to form carbon dioxide, water and releases heat and light.

Answer:

(a) N2(g) + 3H2(g) Fe773 K 2NH3(g), combination reaction(b) NaOH(aq) + CH3COOH(aq)  CH3COONa(aq) + H2O(l), double displacement reaction or neutralization reaction(c) C2H5OH(aq) + CH3COOH(aq) H2SO4 CH3COOC2H5(aq) + H2O(l), esterification reaction or double displacement reaction or condensation reaction(d) C2H4(g) + 3O2(g) 2CO2(g)+ 2H2O(g) + Heat + Light, redox reaction

Page No 5:

Question 20:

Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
(a) Thermit reaction, iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide.
(b) Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride.
(c) Chlorine gas is passed in an aqueous potassium iodide solution to form potassium chloride solution and solid iodine.
(d) Ethanol is burnt in air to form carbon dioxide, water and releases heat.

Answer:

(a) Fe2O3(s)+ 2Al(s)  Al2O3(s) + 2Fe(l) + Heat, displacement reaction or redox reaction(b) 3Mg(s)+ N2(g)  Mg3N2(s), combination reaction(c) Cl2(g) + 2KI(aq)  2KCl(aq) + I2(s), displacement recation or redox reaction(d) C2H5OH(aq) + 3O2(g)  2CO2(g) + 3H2O(g) + Heat, redox reaction or combustion reaction

Page No 5:

Question 21:

Complete the missing components/variables given as x and y in the following reactions
(a) Pb(NO3)2 (aq) + 2KI(aq) → PbI2 (x) + 2KNO3(y)
(b) Cu(s) + 2Ag NO3(aq) → Cu(NO3)2(aq) + x(s)
(c) Zn(s) + H2SO4(aq) → ZnSO4(x) + H2(y)
(d) CaCO3s xCaOs+CO2g

Answer:

(a) Pb(NO3)(aq) + 2KI (aq) → PbI(s) + 2KNO(aq)
(b) Cu (s) + 2AgNO(aq) → Cu(NO3)2(aq) + 2Ag (s)
(c) Zn (s) + H2SO(aq) → ZnSO(aq) + H(g)
(d) CaCO3s heatCaOs+CO2g

Page No 5:

Question 22:

Which among the following changes are exothermic or endothermic in nature?
(a) Decomposition of ferrous sulphate
(b) Dilution of sulphuric acid
(c) Dissolution of sodium hydroxide in water
(d) Dissolution of ammonium chloride in water

Answer:

(a) Endothermic reaction
(b) Exothermic reaction
(c) Exothermic reaction
(d) Endothermic reaction

Page No 5:

Question 23:

Identify the reducing agent in the following reactions
(a) 4NH3 + 5O2 → 4NO + 6H2O
(b) H2O + F2 → HF + HOF
(c) Fe2O3 + 3CO → 2Fe + 3CO2
(d) 2H2 + O2 → 2H2O

Answer:

(a) NH3 is causing the reduction of Oto H2O so, ammonia is the reducing agent.
(b) H2O is causing the reduction of F to HF so, water is the reducing agent.
(c) CO is causing the reduction of Fe2O3 to Fe so, carbon monoxide is the reducing agent.
(d) H2 is causing the reduction of O2 to H2O so, hydrogen is the reducing agent.



Page No 6:

Question 24:

Identify the oxidising agent (oxidant) in the following reactions
(a) Pb3O4 + 8HCl → 3PbCl2 + Cl2 + 4H2O
(b) 2Mg + O2 → 2MgO
(c) CuSO4 + Zn → Cu + ZnSO4
(d) V2O5 + 5Ca → 2V + 5CaO
(e) 3Fe + 4H2O → Fe3O4 + 4H2
(f) CuO + H2 → Cu + H2O

Answer:

(a) Pb3O4 is the oxidising agent.
(b) O2 is the oxidising agent.
(c) CuSO4 is the oxidising agent.
(d) V2Ois the oxidising agent.
(e) H2O is the oxidising agent.
(f) CuO is the oxidising agent.

Page No 6:

Question 25:

Write the balanced chemical equations for the following reactions

  1. Sodium carbonate on reaction with hydrochloric acid in equal molar concentrations gives sodium chloride and sodium hydrogencarbonate.
  2. Sodium hydrogencarbonate on reaction with hydrochloric acid gives sodium chloride, water and liberates carbon dioxide.
  3. Copper sulphate on treatment with potassium iodide precipitates cuprous iodide (Cu2 I2), liberates iodine gas and also forms potassium sulphate.

Answer:

a. Na2CO3(aq) + HCl(aq)  NaCl(aq) + NaHCO3(aq)b. NaHCO3(aq) + HCl(aq)  NaCl(aq) + H2O(l) + CO2(g)c. 2CuSO4(aq) +4KI(s)  Cu2I2(s) + I2(g) +2K2SO4(aq) 

Page No 6:

Question 26:

A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of the chemical reaction?

Answer:

A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white precipitate of silver chloride and potassium nitrate is formed.
KCl(aq) + AgNO3(aq)  AgCl(s) + KNO3(aq), in this reaction, there is a mutual exchange of cations or the anions is taking place between the two involved reactants. So, this reaction is a double displacement reaction.

Page No 6:

Question 27:

Ferrous sulphate decomposes with the evolution of a gas having a characteristic odour of burning sulphur. Write the chemical reaction involved and identify the type of reaction.

Answer:

Decomposition of ferrous sulphate at a temperature above 750 °C produces ferric oxide along with sulphur dioxide and sulphur trioxide gas.
FeSO4(s) Heat above 750 °C Fe2O3(s) + SO2(g) + SO3(g), in this reaction, ferrous sulphate is decomposing with the application of heat to give ferric oxide, sulphur dioxide and sulphur trioxide. The burning sulphur odour is due to the evolution of sulphur dioxide gas. So, this is a decomposition reaction.

Page No 6:

Question 28:

Why do fire flies glow at night?

Answer:

Fireflies secrets the enzyme luciferase, this enzyme reacts with the protein luciferin that carries out oxidation of magnesium. This reaction occurs in the presence of oxygen gas. Light is emitted due to the oxidation of magnesium. Due to this fireflies glow at night.

Page No 6:

Question 29:

Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?

Answer:

Grapes which are still on the plant are a part of the living system that is the plant and with their defence mechanism completely intact and thus they do not undergo fermentation. Once the grapes are plucked now the defence mechanism that was preventing the fermentation process is no more so, in the presence of a microorganism called yeast fermentation of grapes can be carried out.
In the process of fermentation, sugar is converted to alcohol and carbon dioxide gas according to the following reaction,
C6H12O6(aq) Yeast 2C2H5OH(aq) + 2CO2(g), since there is a change in the chemical composition of sugar present in the grapes to produce alcohol and carbon dioxide gas so, this is a chemical change.

Page No 6:

Question 30:

Which among the following are physical or chemical changes?
(a) Evaporation of petrol
(b) Burning of Liquefied Petroleum Gas (LPG)
(c) Heating of an iron rod to red hot.
(d) Curdling of milk
(e) Sublimation of solid ammonium chloride

Answer:

(a) Physical change
(b) Chemical change
(c) Physical change
(d) Chemical change
(e) Physical change

Page No 6:

Question 31:

During the reaction of some metals with dilute hydrochloric acid, following observations were made.
(a) Silver metal does not show any change
(b) The temperature of the reaction mixture rises when aluminium (Al) is added.
(c) The reaction of sodium metal is found to be highly explosive
(d) Some bubbles of a gas are seen when lead (Pb) is reacted with the acid.
Explain these observations giving suitable reasons.

Answer:

(a) The reactivity of silver is very low as it is placed below hydrogen in reactivity series so it does not react with dilute hydrochloric acid.
(b) The reactivity of silver is very low as it is placed below hydrogen in reactivity series so it does not react with dilute hydrochloric acid.
(c) Sodium is an alkali metal which is one of the most reactive metals and readily reacts with dilute HCl to form NaCl and hydrogen gas. The evolution of hydrogen gas cause explosion.
(d) The reaction of lead metal with dilute HCl forms lead (II) chloride and releases hydrogen gas in the form of bubbles. Since the reaction is quite slow due to less reactivity of lead, only bubbles of H2 are seen to evolve.



Page No 7:

Question 32:

A substance X, which is an oxide of a group 2 element, is used intensively in the cement industry. This element is present in bones also. On treatment with water it forms a solution which turns red litmus blue. Identify X and also write the chemical reactions involved.

Answer:

The substance X is calcium oxide (CaO), also called as quick lime. When calcium oxide is made to react with water it undergoes a fast spontaneous exothermic reaction to form calcium hydroxide Ca(OH)2, also called lime water. As calcium hydroxide is a base so, it turns red litmus blue.

CaO(s) + H2O(l)  Ca(OH)2(aq)

Page No 7:

Question 33:

Write a balanced chemical equation for each of the following reactions and also classify them.
(a) Lead acetate solution is treated with dilute hydrochloric acid to form lead chloride and acetic acid solution.
(b) A piece of sodium metal is added to absolute ethanol to form sodium ethoxide and hydrogen gas.
(c) Iron (III) oxide on heating with carbon monoxide gas reacts to form solid iron and liberates carbon dioxide gas.
(d) Hydrogen sulphide gas reacts with oxygen gas to form solid sulphur and liquid water.

Answer:

(a) (CH3COO)2Pb(aq) +2HCl(aq)  PbCl2(s) + 2CH3COOH(aq), double displacement reaction.(b) 2Na(s) + 2C2H5OH(l)  2C2H5ONa+(aq) + H2(g), displacement reaction.(c) Fe2O3(s) + 3CO(g)  2Fe(s) + 3CO2(g), redox reaction.(d) 2H2S(g) + O2(g)  2S(s) + 2H2O(l), redox reaction.

Page No 7:

Question 34:

Why do we store silver chloride in dark coloured bottles?

Answer:

Silver chloride is a photosensitive chemical substance. When silver chloride gets exposed to light it undergoes a decomposition reaction to form silver metal and chlorine gas so, to prevent the photolysis of silver chloride it is stored in dark coloured bottles.

2AgCl(s) Sunlight 2Ag(s) + Cl2(g)

Page No 7:

Question 35:

Balance the following chemical equations and identify the type of chemical reaction.
(a) Mg(s) + Cl2(g) → MgCl2(s)
(b) HgOs HeatHgl+O2g
(c) Nas+Ss FuseNa2Ss
(d) TiCl4(l) + Mg(s) → Ti(s) + MgCl2(s)
(e) CaO(s) + SiO2(s) → CaSiO3(s)
(f) H2O2l U VH2Ol + O2g

Answer:

(a) Mg(s) + Cl2(g) → MgCl2(s), combination reaction
(b) 2HgOs Heat 2Hgl+O2g, decomposition reaction
(c) 2Nas+Ss FuseNa2Ss, combination reaction
(d) TiCl4(l) + 2Mg(s) → Ti(s) + 2MgCl2(s), displacement reaction
(e) CaO(s) + SiO2(s) → CaSiO3(s), combination recaion
(f) 2H2O2l Uv 2H2Ol + O2g, decomposition reaction

Page No 7:

Question 36:

A magnesium ribbon is burnt in oxygen to give a white compound X accompanied by emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen, it continues to burn and forms a compound Y.
(a) Write the chemical formulae of X and Y.
(b) Write a balanced chemical equation, when X is dissolved in water.

Answer:

(a) When magnesium ribbon is burnt in oxygen it forms magnesium oxide according to the following reaction: 
2Mg(s) + O2(g) Heat 2MgO(s), when this burning ribbon is placed in an atmosphere of nitrogen then it reacts with the nitrogen gas to form magnesium nitride according to the following reaction:
3Mg(s) + N2(g) Mg3N2(s). So, X is MgO and Y is Mg3N2.

(b) When magnesium oxide is dissolved in water, it reacts with water to form magnesium hydroxide.
MgO(s) + H2O(l)  Mg(OH)2(aq)

Page No 7:

Question 37:

Zinc liberates hydrogen gas when reacted with dilute hydrochloric acid, whereas copper does not. Explain why?

Answer:

Zinc is placed higher than hydrogen in the reactivity series while copper is placed below hydrogen, that means zinc is more reactive than hydrogen, but copper is less reactive than hydrogen. So, when zinc is made to react with hydrochloric acid it replaces hydrogen from HCl by undergoing a displacement reaction which forms hydrogen gas, but the same reaction does not occur copper. 
2HCl(aq) + Zn(s)  ZnCl2(aq) + H2(g)HCl(aq) + Cu(s)  No reaction

Page No 7:

Question 38:

A silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining.
(a) Why do silver articles turn black when kept in the open for a few days? Name the phenomenon involved.
(b) Name the black substance formed and give its chemical formula.

Answer:

(a) The metal surface of the silver article reacts with atmospheric sulphur compounds like hydrogen sulphide and form a black layer of sulphides. This phenomenon is called as corrosion or tarnishing of silver.

(b) The black substance that is formed by the reaction of hydrogen sulphide and atmospheric oxygen is silver sulphide (Ag2S).
4Ag(s) + O2(g) + 2H2S(s)  2Ag2S(s) + 2H2O(l)



Page No 8:

Question 39:

On heating blue coloured powder of copper (II) nitrate in a boiling tube, copper oxide (black), oxygen gas and a brown gas X is formed
(a) Write a balanced chemical equation of the reaction.
(b) Identity the brown gas X evolved.
(c) Identity the type of reaction.
(d) What could be the pH range of aqueous solution of the gas X?

Answer:

(a) 2Cu(NO3)2(s) Heat 2CuO(s) + O2(g) + 4NO2(g)
​(b) The brown gas X that is involved in the reaction is nitrogen dioxide.
(c) In this reaction copper (II) nitrate is undergoing a thermal decomposition reaction.
(d) In water, if NO2 gas is dissolved it tends to produce nitric acid and nitrous acid, both of which are acidic in nature and thus the pH of the solution would be less than 7.

Page No 8:

Question 40:

Give the characteristic tests for the following gases
(a) CO2
(b) SO2
(c) O2
(d) H2

Answer:

(a) When carbon dioxide gas is passed through an aqueous solution of calcium hydroxide if reacts to form an insoluble white chemical compound calcium carbonate and the solution turns milky white. This phenomenon is also known as turning lime water milky and is the identification test for carbon dioxide gas.
CO2(g) + Ca(OH)2(aq)  CaCO3(s) + H2O(l)

(b) When an acidified potassium dichromate solution, which is orange in colour due to the presence of Cr2O72- ion is added to sulphur dioxide gas it reduces the potassium dichromate solution to chromium (III) sulphate which is green in colour, thus the orange colour of the solution change to green and this reaction acts as identification test for sulphur dioxide gas.
K2Cr2O7 + H2SO4 + 3SO2  K2SO4 + Cr2(SO4)3 + H2O

(c) Oxygen gas is a supporter of combustion so, if glowing split is inserted into a conical flask containing oxygen gas then the splint reignites. This simple test acts very effectively as an identification test for oxygen gas.
C(s) + O2(g)  CO2(g) + heat + light, here C represent wooden glowing splint.

(d) Hydrogen gas has the highest calorific values of all the combustible gases and even a very small quantity of hydrogen gas is capable of producing an explosive combustion reaction. When hydrogen gas is burnt in an atmosphere of oxygen it always burns with a pop sound. This combustion reaction acts as an identification test for hydrogen gas.
O2(g) + 2H2(g)  2H2O(g)  H = -484 Kjmol 
 

Page No 8:

Question 41:

What happens when a piece of
(a) zinc metal is added to copper sulphate solution?
(b) aluminium metal is added to dilute hydrochloric acid?
(c) silver metal is added to copper sulphate solution?

Also, write the balanced chemical equation if the reaction occurs

Answer:

(a) When zinc metal is added to copper (II) sulphate solution, zinc being more reactive than copper will replace copper from its salt to form zinc (II) sulphate and the colour of the solution changes from blue to colourless and the brown colour copper metal gets deposited at the bottom.
CuSO4(aq) + Zn(s)  ZnSO4(aq) + Cu(s)

(b) Aluminium metal being a highly reactive metal is capable of displacing hydrogen from its compound to form aluminium chloride salt with the evolution of hydrogen gas.
2Al(s) + 6HCl(aq)  AlCl3(aq) + 3H2(g) 

(c) Silver metal is a less reactive metal when compared with copper, thus when silver is added to copper sulphate solution no reaction would occur.
CuSO4(aq) + Ag(s) No reaction

Page No 8:

Question 42:

What happens when zinc granules are treated with dilute solution of H2SO4, HCl, HNO3, NaCl and NaOH, also write the chemical equations if reaction occurs.

Answer:

Zinc reacts with dilute sulphuric acid to form zinc sulphate and hydrogen gas.
Zn(s) + H2SO4(aq)  ZnSO4(aq) + H2(g)

Zinc reacts with dilute hydrochloric acid to form zinc chloride and hydrogen gas.
Zn(s) + 2HCl → ZnCl2(aq) + H2(g)

Zinc reacts with dilute nitric acid to form zinc nitrate and hydrogen gas.
Zn(s) + 2HNO3(aq) Zn(NO3)2(aq) + H2(g)

Zinc does not react with sodium chloride salt.

Zinc reacts with sodium hydroxide to form sodium zincate and hydrogen gas.
Zn(s) + 2NaOH(aq)  Na2ZnO2(aq) + H2(g)

Page No 8:

Question 43:

On adding a drop of barium chloride solution to an aqueous solution of sodium sulphite, white precipitate is obtained.
(a) Write a balanced chemical equation of the reaction involved
(b) What other name can be given to this precipitation reaction?
(c) On adding dilute hydrochloric acid to the reaction mixture, white precipitate disappears. Why?

Answer:

(a) BaCl2(aq) + Na2SO3(aq)  BaSO3(s) + 2NaCl(aq) 
(b) This precipitation reaction could also be named as a double displacement reaction.
(c) On adding dilute hydrochloric acid to the mixture makes barium sulphite to react and form barium chloride which is soluble in water and thus the white precipitate disappears.
BaSO3(s) + 2HCl(aq)  BaCl2(aq) + H2O(l) + SO2(g)

Page No 8:

Question 44:

You are provided with two containers made up of copper and aluminium. You are also provided with solutions of dilute HCl, dilute HNO3, ZnCl2 and H2O. In which of the above containers these solutions can be kept?

Answer:

The reaction of the given compounds with the copper container:

Dilute HCl: Copper exhibits no reaction with HCl so it can store in a copper container.

Dilute HNO3: With dilute nitric acid, copper metal forms copper nitrate with nitric oxide and water so dilute nitric acid cannot store in a copper container. 
Cu(s) + 4HNO3(aq)  Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l)

ZnCl2: Since Cu metal is less reactive than Zn so it cannot displace Zn from its compounds and there will be no reaction. Hence zinc chloride can store in a copper container.

H2O: There is no reaction between water and copper metal at room temperature so water can store in a copper container.

The reaction of the given compounds with aluminium container:

Dilute HCl: Aluminium reacts with Al reacts with dilute HCI and form aluminium chloride with hydrogen gas so it cannot be stored in an aluminium container.
2Al(s) + 6HCl(aq)  2AlCl3(aq) + 3H2(g)

Dilute HNO3: Nitric acid is an oxidizing agent and in the presence of it, aluminium metal forms a protective layer of oxide so it will not react further. Hence dilute nitric acid can store in an aluminium container.

ZnCl2:  Aluminium readily reacts with zinc chloride and forms aluminium chloride with zinc metal.
2Al(s) + 3ZnCl2(aq)  2AlCl3(aq) + 3Zn(s)

H2O: At room temperature, there will be no reaction between aluminium metal and water so it can store in an aluminium container.



View NCERT Solutions for all chapters of Class 10