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

NCERT Solutions Class 10 for Science Chapter 1 Chemical Reactions and Equations : In this post, we will share with you all the detailed NCERT Solutions of Class 10 Science Chapter 1 Chemical Reactions and Equations. This will contain both in-text and back-exercise questions for Science and Social Science, and all exercise questions for Mathematics. For all school and board level examinations, doing all the NCERT Questions is a must.

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NCERT Questions and Answers not only help you get hold of concepts firmly and enhance your understanding, but also form the base of all types of questions asked in exams. Questions asked in exam are more or less the same type as mentioned in NCERT. Moreover, sometimes the questions in NCERT are directly asked in exams, as it is, without any changes.

Hence, it’s very important to understand NCERT Questions and Answers.

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Class 10 Science Chapter 1 – Chemical Reactions and Equations


In-Text Questions SET 1 (Page 6)

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

Answer 1:
Magnesium ribbon should be cleaned before burning in air because Magnesium metal reacts with the atmospheric oxygen and forms Magnesium Oxide (MgO) layer which is a very stable compound. In order to prevent further reactions with Oxygen, it is therefore necessary to clean the ribbon by to remove the layer of MgO.

Question 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

Answer 2:
i) H2 + Cl2 → 2HCl

ii) 3BaCl2 + Al2(SO4)3 →3BaSO4 + 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 solution of Sodium chloride.
ii) Sodium hydroxide solution in water reacts with hydrochloric acid solution to produce Sodium chloride solution and water.

Answer 3:
i) BaCl2 + Na2SO4 → BaSO4 + 2NaCl

ii) NaOH + HCl → NaCl + H2O

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In -Text Questions SET 2 (Page 10)

Question 1:
A 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.

Answer 1:
i) The substance ‘X’ which is used in whitewashing is quick lime or Calcium Oxide and its formula is CaO.

ii) CaO + H2O → Ca(OH)2

Question 2:
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.

Answer 2:
In Activity 1.7, water is electrolysed to give H2 gas at one electrode and O2 gas at the other electrode.
2H2O(l) → 2H2(g) + O2(g)
Thus two molecules of water on electrolysis give two molecules of hydrogen gas and one molecule of oxygen gas or in other words the amount of hydrogen gas collected would be double than that of oxygen gas.

In-Text Questions SET 3 (Page 13)

Question 1:
Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

Answer 1:
When an iron nail dipped in the copper sulphate solution, iron displaces copper from the copper sulphate because iron is more reactive than copper. Therefore the colour of the copper sulphate solution changes. The reaction is:
Fe + CuSO4 → FeSO4 + Cu

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

Answer 2:
Sodium hydroxide and hydrochloric acid react to form sodium chloride and water.

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

(i) 4Na(s) + O2(g) → 2Na2O(s)
(ii) CuO (s) + H2(g) → Cu (s) + H2O(l)

Answer 3:
(i) Substances oxidised is Na as it gains oxygen and oxygen is reduced.
(ii) Substances reduced is Cu as hydrogen is oxidised as it gains oxygen

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Exercise Questions (Page 14-16)

Question 1:
Which of the statements about the reaction below are incorrect ?
2 PbO(s) + C(s) → 2Pb (s) + CO2(g)
(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

Answer 1:
(i) (a) and (b)
Explanation: (a) because Oxygen is being removed and (b) because the removed oxygen from Lead is added to the elemental Carbon.

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

Answer 2:
(d) Displacement reaction.
Explanation: The Oxygen from the Ferrous oxide is getting displaced to the Aluminium metal to form Aluminium Oxide. In this reaction Aluminum is more reactive metal than Fe. Therefore Al will displace Fe from its oxide. This type of chemical reactions in which one of the elements displace another is called displacement reaction. Here less reactive metal is displaced by more reactive metal. Since one-time displacement is occurring, therefore, it is called a single displacement reaction.

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.

Answer 3:
(a) Hydrogen gas and Iron chloride are produced.
Explanation: The Chlorine from Hydrogen chloride is displaced by the Iron fillings to undergo the following reaction.

2HCl + Fe → FeCl2 + H2

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

Answer 4:
A balanced chemical equation has an equal number of atoms of different elements in the reactants and products.
The chemical equations should be balanced to satisfy the law of conservation of mass.

Question 5:
Translate the following statements into chemical equations and 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.

Answer 5:
a) 3H2 (g) + N2 (g) → 2NH3 (g)
(b) H2S (g) + 3O2 (g) → SO2 (g) + 2H2O(l)
(c) 3BaCl2 (aq) + Al2(SO4)3 (aq) → 2AlCl3 (aq) + 3BaSO4 ↓(s)
(d) 2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g)

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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

Answer 6:
(a) 2HNO+ Ca(OH)→ Ca(NO3)+ 2H2O
(b) 2NaOH + H2SO→ Na2SO+ 2H2O
(c) NaCl + AgNO→ AgCl + NaNO3
(d) BaCl+ H2SO→ BaSO+ 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

Answer 7:
(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

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)

Answer 8:
(a) 2KBr (aq) + Bal2(aq) → 2Kl(aq) + BaBr2(s)
Type : Double displacement reaction
(b) ZnCO3 (s) → ZnO (s) + CO2 (g)
Type : Decomposition reaction
(c) H2 (g) + Cl2 (g) → 2HCl(g)
Type : Combination reaction
(d) Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)
Type : Displacement reaction

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

Answer 9:
An endothermic reaction occurs when energy is absorbed from the surroundings in the form of heat.(Example: Photosynthesis, melting of ice, evaporation). Conversely, an exothermic reaction is one in which energy is released from the system into the surroundings. (Example: Explosions, concrete setting, nuclear fission and fusion).

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

Answer 10:
For the survival of life, we require energy. We obtain this energy from the food we eat. The food
molecules, through the process of digestion, is broken down into a simpler molecule like glucose. These
substances come in contact with the Oxygen present in our body cells to form Carbon dioxide and water
along with a certain amount of energy (Respiration process). Since the energy is in the form of heat (that
maintains our body temperature) the respiration is considered to be an exothermic reaction. The reaction
taking place is:
C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy

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

Answer 11:
Combination reaction is said to be the reaction between two or more molecules to form a larger
molecule; whereas the decomposition reaction is defined as the splitting of larger molecules into two or
more smaller molecules. This essentially explains that the decomposition reaction is the opposite of the
combination reaction.
In most of the cases the decomposition reaction is endothermic since heat from the surrounding or
induced heat is used to break the bonds of the larger molecule. Few examples of decomposition
reactions are:
ZnCO3 → ZnO + CO2
CaCO3 + Energy → CaO + CO2
2HgO → 2Hg + O2

Question 12:
Write one equation each for the decomposition reactions where energy is supplied in the form of heat, light or electricity.
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)]

Answer 12:

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

Answer 13:
A displacement reaction is the one when a more reactive substance displaces a less reactive one from its salt
solution whereas a double displacement reaction is the one where a mutual exchange of ions happens between
two compounds.
In a displacement reaction, only a single displacement takes place whereas in the double displacement reaction,
as the name suggests two displacement takes place between the molecules.
Displacement reaction
Mg + 2HCl → MgCl2 + H2
Double displacement reaction
2KBr + BaI2 → 2KI + BaBr2

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.

Answer 14:
Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag(s)

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

Answer 15:
When two solutions containing soluble salts are combined, a double displacement reaction takes place in which the ions are exchanged between the compounds. When one of such compounds formed is in solid form (that is insoluble in aqua) then it settles down at the bottom of the container. This solid is known as the precipitate and the respective reaction is termed as the precipitation reaction. Few examples of precipitation reactions are:

CdSO4(aq) + K2S(aq) → CdS(s) + K2SO4(aq)
2NaOH(aq) + MgCl2(aq) → 2NaCl(aq) + Mg(OH)2(s)

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

Answer 16:
(a) In a chemical reaction, when the oxygen is added to the element to form its respective oxide it is the
element being oxidised. Example:
4Na(s) + O2(g) → 2Na2O(s)
H2S + O2 → H2O + SO2

(b) In a chemical reaction, when the oxygen is being removed from the compound then it is said to be
reduced. Example:
CuO(s) + H2(g) → Cu(s) + H2O(l)
2HgO → 2Hg + O2

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

Answer 17:
The shiny brown coloured element is the Copper metal (Cu). When the metal is heated in air, it reacts with atmospheric oxygen to form copper oxide. Hence, the black coloured compound is the copper oxide.

2Cu(s) + O2(g) → 2CuO(s)

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

Answer 18:
Iron articles are painted to prevent them from rusting. When left unpainted, the metal surface comes in
contact with the atmospheric oxygen and in the presence of moisture it from Iron(III) oxide. But if painted the surface does not come in contact with moisture and air thus preventing Rusting.

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

Answer 19:
To keep food items fresh and save from getting oxidised, food items are flushed with nitrogen.

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

Answer 20:
(a) Corrosion is a process where a refined metal is oxidised by atmospheric oxygen to form a more stable compound such as oxides. The metal gradually degrades during the corrosion process. Rusting of iron is a good example of corrosion where the iron is converted to Iron oxide. Millions of dollars are spent annually in preventing rusting from bridges and other monuments.

(b) The condition produced by the aerial oxidation of the oil and fat present in the food material that produces an unpleasant taste and smell. The rancidity is retarded when the food is kept inside the refrigerator since the low temperature does not promote the oxidation reaction.


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