# NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

Written by Team Trustudies
Updated at 2021-02-11

Chemical reactions and equations is the first chapter (Chapter 1) of class 10 science. We at Trustudies have designed quality NCERT solutions for class 10 science chapter 1 chemical reactions and equations in great detail with all types of questions covered. The NCERT solutions for class 10 science chapter 1 are meant for all the students who find it difficult to find the solutions and is completely free for all. These solutions are verified by students who have scored more than 90 percent marks in class 10 science to ensure the optimum quality of NCERT solutions for class 10 science chapter 1

Chapter 1(chemical reactions and equations) contains topics like physical changes, chemical changes, types of chemical reactions, combination reactions, decomposition reactions, displacement reactions, double displacement reactions, double displacement reaction, balancing of chemical equations, oxidation, reduction, corrosion, rancidity

The NCERT solutions for class 10 science chapter 1 also has solutions to intext exercise which are present in the middle pages of chapter 1 class 10 science and are very important for class 10 board exams. These exercises are also covered in great detail. We have also provided it separately in another section. You can visit them by clicking the link below

## NCERT solutions for class 10 Science Chapter 1 Chemical Reactions And Equations Exercise

Q1) Which of the statements about the reaction below are incorrect?

$2PbO\left(s\right)+C\left(s\right)$

$?$

$2Pb\left(s\right)+C{O}_{2}$

• (a) Lead is getting reduced.
• (b) Carbon dioxide is getting oxidised.
• (c) Carbon is getting oxidised.
• (d) Lead oxide is getting reduced
• (i) (a) and (b)
• (ii) (a) and (c)
• (iii) (a), (b) and (c)
• (iv) all

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

(i) a and b

Reason -
(a) because oxygen is being removed, and
(b) removed oxygen is being added to carbon

Q2) The below reaction is an example of a

$F{e}_{2}{O}_{3}+2Al?A{l}_{2}{O}_{3}+2Fe$

• (a) combination reaction
• (b) double displacement reaction.
• (c) decomposition reaction
• (d) displacement reaction

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

Option d
Displacement reaction

The oxygen from ferrous oxide is getting displaced to aluminum to form aluminum oxide

Q3). What happens when dilute hydrochloric acid is added to iron fillings? 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.

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

Option - a
The chlorine from the hydrogen chloride is displaced to the iron fillings undergoing following reactions.

$2HCl+Fe?FeC{l}_{2}+{H}_{2}$

Q4). What is a balanced chemical equation? Why should chemical equations be balanced?

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

balanced chemical equation has an equal number of atoms of different elements in the reactants and products.
Example :

$Zn+{H}_{2}SO4?ZnS{O}_{4}+{H}_{2}$

Element Name In Reactants In Products
No. of Zn atoms 1 1
No.of H atoms 2 2
No.of S atoms 1 1
No.of O atoms 4 4

Thus above reaction between zinc and dilute sulphuric acid is a balanced equation. According to the Law of conservation of mass, total mass of the elements present in the reactants must be equal to the total mass of the elements present in products. That’s why a chemical equations should be balanced always.

Q5).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 sulpur 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.

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

$\left(a\right)3{H}_{2}+{N}_{2}?2N{H}_{3}$

$\left(b\right)2{H}_{2}S+3{O}_{2}?2{H}_{2}O+2S{O}_{2}$

$\left(c\right)3BaC{l}_{2}+A{l}_{2}\left(S{O}_{4}{\right)}_{3}$

$?$

$2AlC{l}_{3}+3BaS{O}_{4}$

$\left(d\right)2K+2{H}_{2}O?2KOH+{H}_{2}$

Q6). Balance the following chemical equations

$\left(a\right)\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}HN{O}_{3}+Ca\left(OH{\right)}_{2}$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}Ca\left(N{O}_{3}{\right)}_{2}+{H}_{2}O$

$\left(b\right)\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}2NaOH+{H}_{2}S{O}_{4}$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}N{a}_{2}S{O}_{4}+2{H}_{2}O$

$\left(c\right)\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}NaCl+AgN{O}_{3}$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}AgCl+NaN{O}_{3}$

$\left(d\right)\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}BaC{l}_{2}+{H}_{2}S{O}_{4}$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}BaS{O}_{4}+2HCl$

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

a) Let's count the number of various atoms in reactants and products.

Element Name In Reactants In Products
No. of H atoms 3 2
No.of N atoms 1 2
No.of C atoms 1 1
No.of O atoms 5 7

In this equation, you have to balance the atoms of both sides, so you start with one type of atom and go from there. Since Oxygen has more atoms in the equation, let's try to balance them first and see if that works. Currently, I have 5 total O atoms (3 + 2) on the left side and 7 on the right (6 + 1) Since they are not balanced, I need to put something on the left to give more on that side. Try 2 HNO3, which gives 6 O atoms, and I had 2 from the Ca(OH)2 already, so I have a total of 8 O atoms now. Right side, you need 8 total, but only have 7. Since H20 has only one O atom, if you place a 2 in front of the H20, you have 2 O atoms now.
Equation so far :

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}2HN{O}_{3}+Ca\left(OH{\right)}_{2}$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}Ca\left(N{O}_{3}{\right)}_{2}+2{H}_{2}O$

Again, balance all the atoms for reactants and products. Reactants:
• 2HNO3 has 2 H atoms, 2 N atom and 6 O atoms
• Ca(OH)2 has 1 Ca atom, 2 O atoms and 2 H atoms
• Left side: 4 H atoms, 2 N atoms, 8 O atoms, 1 Ca atom

Products:
Ca(NO3)2 has 1 Ca atom, 2 N atoms, 6 O atoms
2H2O has 4 H atoms (2 x 2), and 2 O atoms
Right side: 1 Ca atom 2 N atoms, 8 O atoms, 4 H atoms
Since the numbers on the left equal the right, you now have a balanced equation, so this must be the answer:

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}HN{O}_{3}+Ca\left(OH{\right)}_{2}$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}Ca\left(N{O}_{3}{\right)}_{2}+{H}_{2}O$

$\left(b\right)\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}NaOH+{H}_{2}S{O}_{4}$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}N{a}_{2}S{O}_{4}+{H}_{2}O$

$\left(c\right)\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}NaCl+AgN{O}_{3}$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}AgCl+NaN{O}_{3}$

$\left(d\right)\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}BaC{l}_{2}+{H}_{2}S{O}_{4}$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}BaS{o}_{4}+HCl$

Q6). Balance the following chemical equations

$\left(a\right)\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}HN{O}_{3}+Ca\left(OH{\right)}_{2}$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}Ca\left(N{O}_{3}{\right)}_{2}+{H}_{2}O$

$\left(b\right)\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}NaOH+{H}_{2}S{O}_{4}$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}N{a}_{2}S{O}_{4}+{H}_{2}O$

$\left(c\right)\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}NaCl+AgN{O}_{3}$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}AgCl+NaN{O}_{3}$

$\left(d\right)\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}BaC{l}_{2}+{H}_{2}S{O}_{4}$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}BaS{O}_{4}+HCl$

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

a) Let's count the number of various atoms in reactants and products.

Element Name In Reactants In Products
No. of H atoms 3 2
No.of N atoms 1 2
No.of C atoms 1 1
No.of O atoms 5 7

In this equation, you have to balance the atoms of both sides, so you start with one type of atom and go from there. Since Oxygen has more atoms in the equation, let's try to balance them first and see if that works. Currently, I have 5 total O atoms (3 + 2) on the left side and 7 on the right (6 + 1) Since they are not balanced, I need to put something on the left to give more on that side. Try 2 HNO3, which gives 6 O atoms, and I had 2 from the Ca(OH)2 already, so I have a total of 8 O atoms now. Right side, you need 8 total, but only have 7. Since H20 has only one O atom, if you place a 2 in front of the H20, you have 2 O atoms now.
Equation so far :

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}2HN{O}_{3}+Ca\left(OH{\right)}_{2}$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}Ca\left(N{O}_{3}{\right)}_{2}+2{H}_{2}O$

Again, balance all the atoms for reactants and products. Reactants:
• 2HNO3 has 2 H atoms, 2 N atom and 6 O atoms
• Ca(OH)2 has 1 Ca atom, 2 O atoms and 2 H atoms
• Left side: 4 H atoms, 2 N atoms, 8 O atoms, 1 Ca atom

Products:
Ca(NO3)2 has 1 Ca atom, 2 N atoms, 6 O atoms
2H2O has 4 H atoms (2 x 2), and 2 O atoms
Right side: 1 Ca atom 2 N atoms, 8 O atoms, 4 H atoms
Since the numbers on the left equal the right, you now have a balanced equation, so this must be the answer:

$\left(b\right)\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}2NaOH+{H}_{2}S{O}_{4}$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}N{a}_{2}S{O}_{4}+{H}_{2}O$

$\left(c\right)\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}NaCl+AgN{O}_{3}$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}AgCl+NaN{O}_{3}$

$\left(d\right)\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}BaC{l}_{2}+{H}_{2}S{O}_{4}$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}BaS{o}_{4}+2HCl$

Q7). 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

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

$\left(a\right)Ca\left(OH{\right)}_{2}+C{O}_{3}?CaC{O}_{3}+{H}_{2}O$

$\left(b\right)2AL+3Cu\left(Cl{\right)}_{2}?AlC{l}_{3}+3Cu$

$\left(c\right)\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}Zn\left(s\right)+2AgN{O}_{3}\left(s\right)$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}Zn\left(N{O}_{3}{\right)}_{2}+2Ag$

$\left(d\right)BaC{l}_{2}+{K}_{2}S{O}_{4}?BaS{O}_{4}+2KCl$

Q8). 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 bromide(s)
• (b) Zinc carbonate(s) ? Zinc oxide(s) + Carbon dioxide(g)
• (c) Hydrogen(g) + Chlorine(g) gives Hydrogen chloride(g)
• (d) Magnesium(s) + Hydrochloric acid(aq)givesMagnesium chloride(aq) + Hydrogen(g)

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

(a)

$\left(a\right)\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}2KBr\left(aq\right)+Ba{I}_{2}\left(aq\right)$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}2KI\left(aq\right)+BaB{r}_{2}$

It is a double displacement reaction
$\left(b\right)ZnC{O}_{3}\left(s\right)?ZnO\left(s\right)+C{O}_{2}\left(g\right)$
It is a decomposition reaction.
$\left(c\right){H}_{2}\left(g\right)+C{l}_{2}\left(g\right)?2HCl$
It is a combination reaction

$\left(d\right)\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}Mg\left(s\right)+2HCl\left(aq\right)$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}MgC{l}_{2}\left(aq\right)+{H}_{2}\left(g\right)$

It is a displacement reaction.

Q10). Why is respiration considered an exothermic reaction ? Explain.

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

In the course of respiration glucose is broken into carbon dioxide and energy is released. That’s why it is considered as an exothermic reaction.

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}{C}_{6}{H}_{12}{O}_{6}\left(aq\right)+6{O}_{2}\left(g\right)$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}6C{O}_{2}\left(aq\right)+6{H}_{2}O\left(L\right)+Energy$

Q11) Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

In a combination reaction two or more substances are combined to form new substance while in the decomposition reaction one substance decomposes into two or more substances. Hence, the decomposition reactions are called opposite of combination reactions
$CaC{O}_{3}\left(S\right)?CaO\left(s\right)+C{O}_{2}\left(g\right)$
This is a Decomposition reaction ${H}_{2}\left(g\right)+C{l}_{2}?2HCl\left(g\right)$
This is a Combination reaction

Q12) Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

$CaC{O}_{3}\left(s\right)?CaO\left(s\right)+C{O}_{2}\left(g\right)$
In this reaction energy is supplied in the form of heat.
$2AgCl\left(s\right)+sunlight?2Ag\left(s\right)+C{l}_{2}\left(g\right)$
In this reaction energy is supplied in the form of light,i.e.sunlight $2{H}_{2}O+electricity?2{H}_{2}+{O}_{2}$
In this reaction energy is supplied in the form of electricity.

Q13) What is the difference between displacement and double displacement reactions? Write equations for these reactions.

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

When a more reactive element displaces a less reactive element from its salt solution, then it is called displacement reaction. While there is an exchange of ions between the reactants to produce new substances, it is called double displacement reaction. In displacement reaction one displacement takes place. While in double displacement reaction two displacements takes place. Following are examples of displacement reaction and double displacement reaction.

$Mg\left(s\right)+2HCl\left(aq\right)?MgC{l}_{2}+{H}_{2}\left(g\right)$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}2KBr\left(aq\right)+BaC{l}_{2}$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}2KCl\left(aq\right)+BaB{r}_{2}$

Q14) In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}2AgN{O}_{3}\left(aq\right)+Cu\left(s\right)$

$?$

$\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}\phantom{\rule{thickmathspace}{0ex}}Cu\left(N{O}_{3}{\right)}_{2}+2Ag\left(s\right)$

The silver nitrate is in solution and the metallic copper will dissolve to form copper nitrate; as it does, it will precipitate the silver in solution as metallic silver. That is, copper is exchanged for the silver in solution and silver is replaced by the copper that is not in solution.

Q15) What do you mean by a precipitation reaction? Explain by giving examples.

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

Reactions in which precipitate is formed are called precipitation reactions. Generally in a precipitation reaction insoluble salts are settled down as precipitate.

$N{a}_{2}S{O}_{4}\left(aq\right)+BaC{l}_{2}\left(aq\right)$

$?$

$2Nacl\left(aq\right)+BaS{O}_{4}\left(s\right)$

In the above reaction, when sodium sulphate reacts with barium chloride, the white precipitate of barium sulphate is formed along with the sodium chloride.

Q16) Explain the following: (a) Oxidation (b) Reduction

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

Oxidation: When a substance gains oxygen or loses hydrogen during a reaction, it is called that the substance is oxidized. This phenomenon is called oxidation. In the following reaction, copper gets oxygen and hence is oxidised.
$2Cu+{O}_{2}+Heat?2CuO$
$CuO+{H}_{2}+Heat?Cu+{H}_{2}O$
In the above reaction hydrogen gains oxygen, and hence oxidized. Reduction: If a substance loses oxygen or gains hydrogen during a reaction, it is that the substance is reduced. This phenomenon is called reduction. In the following reaction zinc loses oxygen, and hence called is reduced.
$ZnO+C?ZnO$ $Mn{O}_{2}+4HCl?MnC{l}_{2}+2{H}_{2}O+C{l}_{2}$ In this reaction Mangnese dioxide loses oxygen and hence is called reduced.

Q17) shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

Copper is a brown coloured shiny element, when heated in air, it becomes black in colour.
$2Cu+{O}_{2}+Heat?2CuO$ Hence, the element ‘X’ is copper and black coloured compound formed is copper oxide.

Q18) Why do we apply paint on iron articles?

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

When articles made of iron come in contact with the moisture present in air, it forms iron oxide, which is known as rust. Hence, to prevent an iron article to come in contact with moisture present in air paint is applied. Paint prevents the iron to get rusted.

Q19) Oil and fat containing food items are flushed with nitrogen. Why?

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

When fats and oils are oxidised, they become rancid and their smell and taste change. Hence, food items containing oil and fat are flushed with nitrogen which prevents them to get oxidized and becoming rancid.

Q.9 What is meant by exothermic and endothermic reactions? Give examples.

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

Chemical reactions that release energy in the form of heat, light, or sound are called exothermic reactions.
Example: Mixture of sodium and chlorine to yield table salt
Reactions that absorb energy or require energy in order to proceed are called endothermic reactions.
For example: In the process of photosynthesis, plants use the energy from the sun to convert carbon dioxide and water to glucose and oxygen.

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

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

(a) Corrosion:
Corrosion is defined as a process where materials, usually metals, deteriorate as a result of a chemical reaction with air, moisture, chemicals, etc.
For example, iron, in the presence of moisture, reacts with oxygen to form hydrated iron oxide.
(b) Rancidity:
The process of oxidation of fats and oils that can be easily noticed by the change in taste and smell is known as rancidity.
For example, the taste and smell of butter changes when kept for long.

## NCERT solutions for class 10 Science Chapter 1 Chemical Reactions And Equations Intext Exercise

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

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

Magnesium ribbon should be cleaned before burning in air because Magnesium metal reacts with oxygen present in the atmosphere and forms a very stable compound i.e, Magnesium Oxide(MgO). In order to prevent further reactions with Oxygen, it is therefore required to clean the ribbon to remove the layer of MgO.

2.Write a balanced equation for the following chemical reactions.
(i) Hydrogen+Chloride?Hydrogen Chloride

(ii) Barium Chloride+Aluminium Sulphate?Barium Sulphate+Aluminium Chloride

(iii) Sodium+Water?Sodium hydroxide+Hydrogen

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

(i)
${H}_{2}+C{l}_{2}?2HCl$

(ii)

$3BaC{l}_{2}+A{l}_{2}\left(S{O}_{4}{\right)}_{3}$

$?$

$2AlC{l}_{3}+3BaS{O}_{4}$

(iii) $2Na+2{H}_{2}O?2NaOH+{H}_{2}$

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 solution of Sodium chloride.

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

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

(i)

$BaC{l}_{2}+N{a}_{2}S{O}_{4}$

$?$

$BaS{O}_{4}+2NaCl$

(ii)$NaOH+HCl?NaCl+{H}_{2}O$

4. A solution of a substance ‘X’ is used for whitewashing.
(i) Name the substance ‘X’ and write its formula.

(ii) Write the reaction of the substance ‘X’ named in (i) above with water.

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

(i) Calcium Oxide or quick lime is the substance used for whitewashing.Hence, the substance ‘X’ is Calcium Oxide and it’s formula is $CaO$.
(ii) $CaO+{H}_{2}O?Ca\left(OH{\right)}_{2}$

5. Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas.

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

(Hydrolysis of water has been performed in the activity 1.7 in the text book.)
When electric current is passed through water it decomposes to release ${H}_{2}and{O}_{2}$ gas , so gas collected in one of the test tubes is double of the amount collected in the other tube.Here, after electrolysis two molecules of Hydrogen and one molecule of Oxygen gas is released, hence the amount of Hydrogen collected would be double than that of Oxygen.

6.Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

Iron is more reactive than copper so, when an iron nail dipped in the copper sulphate solution, iron displaces copper from the copper sulphate. Therefore, the colour of the copper sulphate solution changes. Reaction taking place :
$Fe+CuS{O}_{4}?FeS{O}_{4}+Cu$

7.Give an example of a double displacement reaction other than the one given in Activity 1.10.

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations

$AgN{O}_{3}+NaCl?AgCl+NaN{O}_{3}$ Here silver donates its ion to Sodium and accepts chloride ion to form Silver Chloride and Sodium Nitrate ,so the reaction between silver Nitrate $AgN{O}_{3}$and Sodium Chloride $NaCl$is an example of double displacement reaction.

8. Identify the substances that are oxidised and the substances that are reduced in the following reactions.
(i) $4Na\left(s\right)+{O}_{2}\left(g\right)?2N{a}_{2}O\left(s\right)$

(ii) $CuO\left(s\right)+{H}_{2}\left(g\right)?Cu\left(s\right)+{H}_{2}O\left(l\right)$

NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions And Equations