NCERT Solutions For Class 10 Science | Ch 1 Chemical Reactions and Equations

NCERT Solutions for Class 10 Science

Intext Questions Page no. 6

These are the accurate solutions for intext questions of Class 10 Science NCERT book.

Question 1: Why should be a magnesium ribbon be cleaned before burning in air?

Ans 1: A magnesium ribbon develops a layer of magnsesium oxide ( MgO) when it is kept in air. So, to enable the complete burning of magnesium without any impurity or layer, it is cleaned before using.

Question 2: Write the balanced chemical equations for the following chemical reactions

(i) Hydrogen + Chlorine –> Hydrogen Chloride

(ii) Barium Chloride + Aluminium Sulphate –> Barium Sulphate + Aluminium Chloride

(iii) Sodium + Water –> Sodium hydroxide + Hydrogen

Ans 2:

(i) H2 + Cl2 –> 2HCl

(ii) 3 BaCl2 + Al2(SO4)3 –> BaSO4 + 2AlCl3

(iii) 2Na + 2H2O –> 2NaOH + H2

 Question 3: Write a balanced chemical equation with state symbols for the following reactions:

(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of barium chloride

(ii) Sodium hydroxide solution  ( in water) reacts with a hydrochloric acid solution ( in water) to produce sodium chloride solution and water

Ans 3:

(i) BaCl2 (aq) + Na2SO4 (aq) –> BaSO4 (s) + 2Nacl (aq)

(ii) NaOH (aq) + HCl (aq) –> NaCl (aq) + H2O (l)

Page Number 10 NCERT Solutions for Class 10 Science, Chapter 1

Question 1: A solution of asubstance X is used fir white washing

(i) Name the substance X and write its formula

(ii) Write the reaction of the substance X named inn (i) above with water.

Ans 1.

(i) The name of the substance used for whitewashing is Calcium oxide. It is also known as quick lime CaO

(ii) The formula for the reaction of CaO with H2O is given below:-

CaO (s) + H2O –> Ca(OH)2

Ca(OH)2 is also known as slaked lime.

Question 2: Why is the amount of gas collected in one of the test tubes in textbook Activity 1.1 (i.e electrolysis of water ) double the amount collected in the other? Name the gas { CBSE Delhi 2015 ]

Ans 2:  When water H2O is electrolysed then the process will give hydrogen gas and the oxygen gas.

Let’s see the reaction below:-

H2O ————–>2   H2 (g) + O2 (g)

Electrolysis

When the electrolysis is done H2 gas is collected at one end and oxygen at the other electrode. The amount of H2 gas will always be double the amount of oxygen gas. This is so because even in H20 there are two atoms of H2 gas.

Also Check: Management of Natural Resources Class 10 NCERT Solutions 

NCERT Solutions for Class 10 Science

Page 13 Chemical Reactions and Equations NCERT Back Exercise Questions

Question 1: Why does the colour of Copper Sulphate solution changes when iron nail is dipped into it?

OR

An iron nail is dipped in the solution of copper sulphate solution for about 30 minites, Stat the change in colour observed. Give reasons for  the change.

Ans 1: The colour of Copper Sulphate solution changes when an iron nail is dipped into the solution because of displacement reaction. Fe will displace Copper as it is more reactive. Let’s see the reaction below:-

Fe + CuSO4 –> FeSO4 + Cu (s)

Question 2: Give an example of a double displacement reaction other than the one given in 1.10

( NCERT Text book )

Ans 2: Sodium hydroxide and Hydrochloric acid reacts to give sodium chloride and and water

NaOH (aq) + HCl (aq)   —>    NaCl (aq)  + H2O (l)

Question 3: Identify the substances that are oxidized and the substances reduced in the following reactions. 

(i) 4 Na (s) + O2 –> 2Na2O (s)

(ii) CuO (s) + H2 (g) –> Cu (s) + H2O

Ans

(i) Na Sodium is oxidized and oxygen is reduced.

(ii) Copper Oxide is reduced and Hydrogen is oxidized as it gained Oxygen

Text Book Back Exercise Questions

Question 1: Which of the statements about the reaction below are incorrect?

2PbO (s) + C (s) –> 2Pb (s) + CO2 (g)

(a) Lead is getting reduced

(b) Carbon dioxide is getting oxidized

(c) Carbon is getting oxidized

(d) Lead Oxide is getting reduced

(i) a and b

(ii) a and c

(iii) a b and c

(iv) All of the above

Ans:

(i) a and b

Question 2: Fe2O3+ 2Al –> Al2O3 + 2Fe

The above reaction is an example of a

(a) combination

(b) Double displacement

(c) Decomposition

(d) Displacement reaction

Ans d) Displacement reaction as in this example Aluminium displaces iron.

Question 3: What happens when dilute hydrochloric acid is added to iron filings? Tick the correct answer.

(a) Hydrogen gas and iron chloride are produced

(b) Chlorine gas and iron hydroxide are produced

(c) No reaction takes place

(d) Iron salt and water are produced

Ans 3:

a) Hydrogen gas and iron chloride is produced. Fe is more reactive than hydrogen so it will displace hydrogen.

Question 4: What is a balanced chemical equation? Why should chemical equations be balanced?

Ans 4: A balanced chemical equation is the one in which each element taking part in the reaction has equal number of atoms both on reactant and product side. The equation should also validate the law of conservation of mass.

Question 5: Translate the following statements into chemical equations and then balance them

(a) Hydrogen gas combines with nitrogen to form ammonia

(b) Hydrogen Sulphide gas burns in air to give water and sulphur dioxide

(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.

(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Ans 5:

(a) 3H2 (g) + N2 (g) –> 2NH3 (g)

(b) H2S (g) + 3O2(g) –> SO2 (g) + 2H2O (l)

(c) 3BaCl2  + Al2(SO4)3 –> 2AlCl3 + 3BaSO4

(d) 2K + 2H2O –> 2KOH aq) + H2 (g)

Question 6: Balance the following chemical equations

Balance the following chemical equations :
(a) HNO₃ + Ca (OH)₂ → Ca (NO₃)₂ + H₂O
(b) NaOH + H₂SO₄ → Na₂SO₄ + H₂O
(c) NaCl + AgNO₃ → AgCl + NaNO₃
(d) BaCl₂ + H₂SO₄ → BaSO₄ + HCl

Ans 6:

(a) 2HNO₃ + Ca (OH)₂ → Ca (NO₃)₂ + 2H₂O

( b) 2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O
(c) NaCl + AgNO₃ → AgCl + NaNO₃
(d) BaCl₂ + H₂SO₄ → BaSO₄ + 2HCl

Question 7
Write the balanced chemical equations for the following reactions :
(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
(b) Zinc + Silver nitrate → Zinc nitrate + Silver

(c) Aluminium + Copper chloride → Aluminium chloride + Copper
(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride

Ans 7:

(a) (a) Ca (OH)₂ + CO₂ → CaCO₃ + H₂O
(b) Zn + 2AgNO₃ → Zn(NO₃)₂ + 2 Ag
(c) 2Al + 3 CuCl₂ → 2AlCl₃ + 3 Cu
(d) BaCl₂ + K₂SO₄ → BaSO₄ + 2KCl

So, these are the balanced chemical equations for the reactions.

Question 8
Write the balanced chemical equation for the following and identify the type of reaction in each case :-
(a) Potassium bromide (aq) + Barium iodide (aq) → Potassium iodide (aq) + Barium
(b) Zinc carbonate(s) → Zinc oxide (s) + Carbon dioxide (g) bromide(s)
(c) Hydrogen (g) + Chloride (g) → Hydrogen chloride (g)
(d) Magnesium (s) + Hydrochloric acid (aq) → Magnesium chloride (aq) + Hydrogen (g)

Ans 8

(a) 2KBr (aq) + Bal₂(aq) → 2Kl(aq) + BaBr₂(s)

This reaction is an example of a double displacement reaction

(b) ZnCO₃ (s) → ZnO (s) + CO₂ (g)
This reaction is a decomposition reaction as ZnCO3 decomposes to give zinc oxide and Carbon dioxide.

(c) H₂ (g) + Cl₂ (g) → 2HCl(g)
This is a combination reaction.

(d) Mg (s) + 2HCl (aq) → MgCl₂ (aq) + H₂ (g)
So this one is a Displacement reaction. Magnesium displaces Hydrogen as it is more reactive.

Question 9: What does one mean by exothermic and endothermic reactions? Give examples.

Ans 9: Exothermic reactions are those in which heat energy is released. Example:-

CH4 + O2 → CO2 + H2O + Heat

Endothermic reactions are those in which heat energy is required for the completion of the reaction

Example:-

NH₄Cl (s) + H₂O (l) ⟶ NH₄Cl (aq) – Heat

Question 10: Why is respiration considered an exothermic reaction? Explain.

Ans 10: Respiration is considered as an exothermic reaction because in a respiration process glucose reacts with O2 gas and a specific amount of energy is released. That’s the reason respiration is categorized under the exothermic reactions.

Question 11: Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.

Ans 11: In a combination reaction two reactants react together to give one or more products but in a decomposition reaction reverse happens i.e. a single compound breaks to give two or more products. Let us see by an example:-

2H2 (g) + O2 (g) –>2 H2O (l) ( Combination reaction )

2H2O (l)  –> 2H2 (g) + O2 (g)  ( Decomposition reaction )

Question 12: Write one equation each for the decomposition reactions where energy is supplied in the form of heat, light, or electricity.
OR
Decomposition reactions require energy either in the form of heat or light or electricity for breaking down the reactants. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light and electricity. [CBSE 2015 (Delhi)]

Ans 12: 

1)Water will decompose in elecrolysis to give hydrogen and oxygen gas.

2H2O ———-> 2H2 + O2

electricity

2) Silver chloride will decompose in the presence of sunlight to give Silver and Chlorine

2AgCl ———>  2Ag + Cl2

sunlight

3) CaCO 3 decomposes to give CaO and carbon dioxide on heating

CaCO 3  ——–> CaO + CO2

Question 13: What is the difference between displacement and double displacement reactions? Write equations for these reactions.

Ans 13: In a displacement reaction only a single metal (more reactive one) displaces the less reactive metal and occupies its position whereas in double displacement two metals displace each other and exchange their position. Let us understand with the examples of both.

Displacement Reaction

Na + HCl —-> NaCl + H2

Double Displacement Reaction

NaOH + HCl —> NaCl + H2O

Question 14: In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.

Ans 14: Cu (s) + AgNO3 (aq)  —> Cu(NO3)2 (aq) + Ag (s)

Question 15: What do you mean by a precipitation reaction? Explain by giving examples:

Ans 15. In a precipitation reaction, two ions from different soluble solutions are mixed together and they form an insoluble salt. That insoluble salt is known as a precipitate.

Silver nitrate (AgNO3), when it will be added to a solution containing potassium chloride (KCl), it will form a white precipitate, AgCl.

AgNO₃ (aq) + KCl (aq) → AgCl (s) + KNO₃(aq)

Question 16: A shiny brown colored element ‘X’ on heating in the air becomes black in color. Name the element ‘X’ and the black coloured compound formed.

Ans16: The shiny brown colored element X is copper metal (Cu). When copper metal is heated in air, it forms a black colored compound copper oxide. So, the black colored compound is the copper oxide or copper (II) oxide, CuO.

Question 17: Why do we apply paint on iron articles?

Ans 17: Rusting is a common process with iron objects. Iron objects develop a layer of rust with time. If not paid attention the objects will start becoming weaker due to the effect of rust. To prevent the objects from getting rusted iron articles are painted so that the surface does not come in direct contact of air and moisture.

Question 18: Oil and fat containing food items are flushed with nitrogen. Why?

Ans 18: Packed food and oil-containing foods may become rancid when exposed to air for a long time. It may change the taste and smell of the food. To prevent them from rancidity an inert gas nitrogen is used. This gas is added in all the packed foods so that the food does not get rancid.

Question 19: Explain the following terms with one example each.
a. Corrosion
b. Rancidity

Ans 19:

a) Corrosion: Corrosion is the process of conversion of metals into a more stable form but actually it leads to the degradation of the metals. This degradation may be due to outside environmental factors. Examples of corrosion like rusting of iron objects. When iron is exposed to air and moisture then it may become weak with the passage of time. A layer of rust forms on it.

(b) Rancidity: is the process in which the substance oxides and the taste and smell of the food changes. To prevent the food from becoming rancid we can use nitrogen gas which is an inert gas. You must have noticed that all the packaged items have nitrogen gas in them.

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