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Chapter 1 of class 10 Science is Chemical reactions and equations. In this chapter, you will get to know about different methods for writing chemical equations. You will also learn to balance those equations. This chapter provides an understanding of the different types of chemical reactions like Disproportion reaction, Combination Reaction, etc. This chapter has a total of 20 questions. This will help you to strengthen your concepts regarding balancing chemical equations.

NCERT Solutions for Class 10 Science Chapter 1 by Swiflearn are by far the best and most reliable NCERT Solutions that you can find on the internet. These NCERT Solutions for Class 10 Science Chapter 1 are designed as per the CBSE Class 10th Science Syllabus. These NCERT Solutions will surely make your learning convenient & fun. Students can also Download FREE PDF of NCERT Solutions Class 10 Science Chapter 1. ## NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations PDF

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

Solution:
Magnesium be a very reactive metal it reacts with oxygen and forms a layer of
MgO (magnesium oxide) on the surface of metal. Magnesium oxide is a stable compound and does not react any further. Hence, magnesium ribbon has to be cleaned with sand paper used for removal of this layer.

#### Question 2:Write the balanced equation for the following chemical reactions.(i) Hydrogen + Chlorine → Hydrogen chloride(ii) Barium chloride + Aluminiumsulphate → Bariumsulphate + Aluminumchloride(iii) Sodium + Water → Sodium hydroxide + Hydrogen

Solution: Refer pdf.

#### (ii) Sodium hydroxide solution (in water) reacts with hydrochloric acidsolution (in water) to produce sodium chloride solution and water.

Solution: Refer pdf.

#### Question 1A solution of a substance ‘X’ is used for white washing.(i) Name the substance ‘X’ and write its formula.(ii) Write the reaction of the substance ‘X’ named in (i) above with water.

Solution:
(i) Substance X is calcium oxide (common name quick lime).
Its chemical formula is CaO .
(ii) Calcium hydroxide is formed when Calcium oxide reacts with water to.
This is a combination reaction. 2 ( )2
CaO H O Ca OH + →

#### Question 2:Why is the amount of gas collected in one of the test tubes in Activity 1.7double of the amount collected in the other? Name this gas.

Solution: Refer pdf.

Exercise: 1.3

#### Question 1:Why does the color of copper sulphate solution change when an iron nail isdipped in it?

Solution:
When iron nail is dipped in the copper sulphate
(CuSO4 ) solution, the more reactive metal
(Iron) replaces the less reactive metal (Copper) from the copper sulphate
(CuSO4 ) solution.
Iron then forms a green compound called ferrous sulphate
(FeSO4 ) .
4 4 Fe CuSO FeSO Cu + → +

#### Question 2:Give an example of a double displacement reaction other than the onegiven in Activity1.10.

Solution:
(i)
2 KBr aq BaI aq aq BaBr s ( ) + → + 2 2 ( ) ( ) ( )
(ii)
( 3 2 3 )2
2 2 KI Pb NO PbI KNO + → +

#### Question 3: Identify the substances that are oxidized and the substances that arereduced in the following reactions.(i) 4Na (s) + O2 (g) → 2Na 2O(s)(ii) CuO (s) + H2 (g) → Cu (s) + H2O (l)

Solution:
(i) Sodium [Na] is oxidized and oxygen gets reduced.
4 2 Na s O g Na O s ( ) + → 2 2 ( ) ( )
(ii) Hydrogen (H2) is oxidized to water (H2O) and Copper oxide
( ) Cu O is reduced to copper (Cu).

#### 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

Solution:
As it is clearly evident from the reaction that Pb is getting oxidized and CO2 is getting reduced.
Thus, (i) (a) and (b) is correct answer.

#### Question 2:Fe2O3 + 2Al → Al2O3 + 2Fe the above reaction is an example of a(a) Combination reaction.(b) Double displacement reaction.(c) Decomposition reaction.(d) Displacement reaction.

Solution:
(d) This is an example of a displacement reaction.

#### Question 3:What happens when dilute hydrochloric acid is added to iron filings? Tickthe 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.

Solution:
(a) Hydrogen gas [H2] and iron chloride [FeCl2]. The reaction is as follows:
Fe + 2HCl → FeCl2 + H2

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

Solution:
In a balanced chemical reaction, the net mass of the reactants should be equal to the net mass of products and the number of atoms in the reactants side should be equal to the number of atoms in products side.
A chemical equation must be balanced to follow the Law of Conservation of mass.

#### Question 5: Translate the following statements into chemical equations and thenbalance them.(a) Hydrogen gas combines with nitrogen to form ammonia.(b) Hydrogen sulphide gas burns in air to give water and sulpurdioxide.(c) Barium chloride reacts with aluminium sulphate to give aluminiumchloride and a precipitate of barium sulphate.(d)Potassium metal reacts with water to give potassium hydroxide andhydrogen gas.

Solution:
(a)
N2(g) + 3H2(g) → 2NH3(g) + Heat
Nitrogen + Hydrogen → Ammonia

(b)
2H2S(g) + 3O2(g) → 2H2O(aq)+2SO2(g)
Hydrogen sulphide + oxygen → Water + sulpur dioxide

(c)
Al2(SO4)3(aq) +3BaCl2(aq) → 2AlCl3(aq) + 3BaSO4(s)
Aluminium sulphate + Barium chloride → Aluminium chloride + Barium sulphate

(d)
2K(s) + 2H2O → 2KOH(aq) + H2(g)
Potassium + water → potassium + hydroxide

#### Question 6: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

Solution: Refer pdf.

#### 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) Aluminum + Copper chloride →Aluminum chloride + Copper(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassiumchloride

Solution:
(a Calcium hydroxide + Carbon dioxide Ca ) → lcium carbonate + Water
The balanced reaction is
Ca (OH)2 + CO2 → CaCO3 + H2O

(b Zinc +Silver nitrate Zinc nitrate +Sil ) → ver
Zn + AgNO3 → Zn(NO3)2 + Ag
Zn + 2AgNO3 → Zn(NO3)2 + 2Ag

(c) Aluminum +Copper chloride → Aluminum chloride+ Copper
Al + CuCl2 → AlCl3 + Cu
2Al + 3CuCl2 → 2AlCl3 + 3Cu

(d Barium chloride + Potassium sulphate ) → Barium sulphate + Potassium Chloride
BaCl2+K2SO4 → BaSO4+ KCl
BaCl2+K2SO4 → BaSO4+ 2KCl

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

Solution:
(a)
KBr (aq)+ BaI2(aq)→ KI (aq) + BaBr2(s)
2KBr (aq)+ BaI2 (aq)→2 KI (aq) + BaBr2(s)
Thisis a double displacement reaction.

(b)
ZnCO3(s)→ZnO(s)+CO2 (g)
This is a decomposition reaction.

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

(d)
Mg(s)+ HCl(aq)→MgCl2(aq)+H2(g)
Mg(s)+2HCl(aq)→MgCl 2 (aq)+H2(g)
This is a single displacement reaction.

#### Question 9:What does one mean by exothermic and endothermic reactions? Giveexamples.

Solution:
Exothermic Reaction: The reactions in which heat is released alongside with the formation of products are termed as exothermic reaction. Here, the energy of the reactants is more than that of the products. i.e. Energy of reactants > energy of products
Example: combustion of methane
CH4(g) + 2O2(g) → CO2 + 2H2O + heat
Endothermic Reaction: The reaction in which energy is absorbed by the reactants to complete the reaction is called endothermic reaction. Here, the energy of the reactants is less than that of theproducts. i.e. Energy of reactants < energy of products
Example: Photosynthesis

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

Solution:
As explained in previous question exothermic reactions release heat or energy. During digestion, the food is broken to form glucose. Glucose then combines with oxygen in the cells of our body and provides energy. This reaction is termed as respiration. Since energy is released along the products it is an exothermic reaction
Glucose + oxygen → CO2 + water + heat

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

Solution:
In a Decomposition reaction a single reactant breaks down into various products.
Example: Decomposition of calcium carbonate [CaCO3]to form calcium oxide [CaO] and carbon dioxide [CO2]
CaCO3 + Energy →CaO + CO2
On the other hand, Combination reactions are those reactions in which two or more reactants combine to form a single product.
Example: Combination of Calcium oxide and carbon dioxide to produce calcium carbonate.
CaO+ CO2 → CaCO3 + energy

#### Question 12:Write one equation each for decomposition reactions where energy issupplied in the form of heat, light or electricity.

Solution:
(i) Thermal decomposition
CaCO3 + heat → CaO+ C
(ii) Electrical decomposition
2H2O + electricity → 2H2 + O2
(iii) Photolytic decomposition
2AgCl + sunlight →2Ag + Cl2

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

Solution:  Refer pdf.

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

Solution: Refer pdf.

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

Solution:
A reaction in which an insoluble matter is formed is called a precipitation reaction. Example 1: On mixing Na2CO3 solution with CaCl2 solution, a white precipitate of CacO3 is formed.
Na2CO3+ CaCl2→CaCO3 + 2NaCl

#### Question 16:Explain the following in terms of gain or loss of oxygen with two exampleseach.(a) Oxidation (b) Reduction

Solution:
Oxidation: Addition of oxygen or electronegative element to a atom, molecule, or ion or removal of hydrogen or electropositive element from an atom, molecule, orion is called oxidation.
Example: CO2+ H2 → CO+H2O (addition of O)
Reduction: Addition of hydrogen or electropositive element to an atom, molecule, or ion or removal of
Oxygen or electronegative element from a atom, molecule, or ion is called reduction.
Example: CO2 + H2 → CO+H2O
CuO+ H2 → Cu+H2O

#### Question 17:A shiny brown colored element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black colored compound formed.

Solution:
Copper (Cu) is the given element X and the black color compound is copper (II) oxide (CuO).
Here copper reacts with oxygen to form the copper (II) oxide.
2Cu + O2 → 2CuO
Shiny brown black

#### Question 18:Why do we apply paint on iron articles?

Solution:
Iron articles get corroded easily in the presence of moisture and air. To prevent rusting, we have to
paint iron Articles. When we apply paint on the iron articles it cuts the contact of moisture and air with the surface and prevents corrosion.

#### Question 19:Oil and fat containing food items are flushed with nitrogen. Why?

Solution:
Oil and fat containing food items get oxidized easily when they come in contact with oxygen. On the other hand nitrogen is an inert gas thus does not react easily. So the packets are flushed with nitrogen which replaces oxygen inside the packets. In this way, we can preserve food containing oil and fats for a long time.

#### Question 20:Explain the following terms with one example each.(a) Corrosion(b) Rancidity

Solution:
(a) Corrosion: Corrosion is defined as a natural process in which the substance, usually metals oxidizes in the presence of air and moisture .Metal converts into its hydrated oxide.
Ex: Iron.
(b) Rancidity: Rancidity is defined as a process in which fats and oils are oxidized. This can be identified by change in taste and smell. For example, when you will keep for a long time any chips packet then the taste and smell of chips changes. 