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

In this article we will share NCERT Class 10th Science Solutions Chapter 1 Chemical Reactions and Equations Textbook Exercise, Questions and Answers, tick the correct, fill in the blanks or additional important Questions. These solutions are solved from latest edition book by subjects experts.

NCERT 10th Science Chapter 1 Intext Questions

In-text Questions (Page 6)

Question 1.
Why should magnesium ribbon be cleaned before v burning in air ?
Answer:
Magnesium ribbon should be cleaned to remove the dust particles present at the upper surface and so that the surface comes directly in contact with air.

Question 2.
Write the balanced equation for the following chemical reactions :

  1. Hydrogen + chlorine → Hydrogen chloride
  2. Sodium + water → Sodium hydroxide + hydrogen

Answer:

  1. H2 + Cl2 → 2HCl
  2. 2Na + 2H2O → 2NaOH + H2

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

  1. Solution of barium chloride and sodium sulphate in water to give insoluble barium sulphate and the solution of sodium chloride.
  2. Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.

Answer:

  1. BaCl2(l) + Na2SO4(aq) → BaSO4(s) + 2NaCl(l)
  2. NaOH(aq) + HCl(aq) → NaCl(l) + H2O(l)

Intext Questions (Page 10)

Question 1.
Why does the colour of copper sulphate solution change when an iron nail is dipped in it ?
Answer:
The colour of copper sulphate solution is changed when an iron nail is dipped in it because iron sulphate is formed by the displacement of copper by iron.
CuSO4(aq) + Fe → FeSO4 + Cu

Question 2.
Give an example of a double displacement reaction other than the one given in activity 1.10.
Answer:
When lead II nitrate is mixed with potassium iodide, potassium nitrate and lead iodide are formed.
Pb(NO3)2 + 2KI → 2KNO3 + Pbl2

Question 3.
Identify the substance that are oxidised and the substances that are reduced in the following reactions :
1. 4Na(s) + O2(g) → 2Na2O(s)
2. CuO(s) + H2(g) → Cu(s) + H2O(Z)
Answer:
1. Sodium (Na) is oxidised into Na2O.
2. CuO (copper oxide) is reduced into Cu, while H2 (Hydrogen) is oxidised into water (H2O).

NCERT Class 10th Science Chapter 1 Textbook Questions and Answers

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 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:
(i) a and b.

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:
(d) 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:
(d) Hydrogen gas and iron chloride are produced.

Question 4.
What is a balanced chemical equation? Why should chemical equations be balanced?
Answer:
When the number of atoms of different elements on both sides of a chemical equation are equal, it is called a balanced equation., Chemical equations should be balanced because a balanced chemical equation tells us the actual information about the equation and actual number of reactants and products.

Question 5.
Translate the following statements into balanced chemical equations.
(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphide 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:
(a) N2(g) + 3H2(g) → 2NH3(g)
(b) 2H2S(g) + 3O2(g) → 2H2O(l) + 2SO2(g)
(c) 3BaCl2 + A12(SO4)3 → 3BaSO4 + 2AlCl3
(d) 2K + 2H2O → 2KOH + H2(g)

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 → BaSO2 + HCl
Answer:
(a) 2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O
(b) 2NaOH + H2S04 → Na2SO4 + 2H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + 2HCl

Question 7.
Write balanced chemical equations for the following reactions:
(а) 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:
(a) Ca(OH2) + CO2 → CaCO3 + HaO
(b) Zn + 2AgNO3 → Zn(NO3)2 + 2Ag
(c) 2A1 + 3CUCl2 → 2AlCl3 + 3Cu
(d) BaCl2 + K2SO4 → BaSO4 + 2KCl

Question 8.
Write the balanced chemical equations for the following and identify the type of the reaction in each case.
(а) Potassium bromide(ag) + barium iodide(aq) → potassium iodide(aq) + barium bromide(aqr)
(b) Zinc carbonate(s) + zinc oxide(s) → carbon dioxide(g)
(c) Hydrogen(g) + chlorine(g) → hydrogen chloride(g)
(d) Magnesium(s) + hydrochloric acid(aqr) → magnesium chloride(aq) + hydrogen(g)
Answer:
(a) 2KBr(ag) + Bal2(ag) → 2KI(aq) + BaBr2(ag)
(b) ZnCO3(s) → ZnO(s) + CO2(g)
(c) H2(g) + Cl2(g) → 2HCl (g)
(d) Mg(s) + 2HCl(ag) → MgCl2(aq) + H2(g)

Question 9.
What does one mean by exothermic and endothermic reactions ? Give examples.
Answer:
Exothermic reactions : Those reactions in which energy is released are called exothermic reactions.
Examples :
1. All combustion reactions like
CH4 + 2O2 → CO2 + 2H2O + Heat

2. Thermite reactions like
2A1 + Fe2O3 → 2Fe + Al2O3 ‘+ Heat
Endothermic reactions : Those reactions in which energy is utilised are called endothermic reactions.

(i) C (s) + 2S (s) → CS2 (l) – Heat
(ii) N2 (g) + O2 (g) → 2NO(g) – Heat

Question 10.
Why is respiration considered an exothermic reaction ? Explain.
Answer:
In respiration, food is broken or oxidised in the presence of oxygen inhaled. In this process, energy is liberated. So respiration is called an exothermic reaction.
C2H12O6 + 6O2 → 6CO2 + 6H2O + Energy

Question 11.
Why are decomposition reactions called the opposite of combination reactions ? Write equations for these reaction.
Answer:
Decomposition reactions are those reactions in which a compound is broken into two Or more new compounds.

NCERT Solutions

Combination reactions are those reactions in which two substances are combined to form a new substance.
CaO + CO2 → CaCO3
In above examples, both the reactions are same but show opposite directions; so decomposition reaction is called the opposite of combination reaction.

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

NCERT Solutions

Question 13.
What is the difference between displacement and double displacement reactions ? Write equations for these reactions.
Answer:
In displacement reaction, one element from its salt is displaced by a more reactive element. For example in following reaction, Cu is displaced by Zn from CuSO4 because Zn is more reactive.
CuSO4 + Zn → ZnSO4 + Cu
In double displacement reaction, exchange of ions takes place between two reactants to forms new products.
Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)

Question 14.
In the refining of silver, the recovery of silver from silver nitrate solution involves displacement by copper metal. Write down the reaction involved.
Answer:
When copper is mixed in silver nitrate solution, it displaces the silver becaiise copper is more reactive than silver.
2AgNO3+ Cu → CU(NO3)2 + Ag

Question 15.
What do you mean by a precipitation reaction ? Explain giving examples.
Answer:
The reactions in which a precipitate is formed are called precipitation reactions.
Examples :
1. Na2SO4(aq) + BaCl2(aq) → BaSO3(s) + 2NaCl(ag) (Precipitate)
2. Pb(NO3)2 + 2KI → 2KNO3 + PbI2

Question 16.
Explain the following terms of gain or loss of oxygen with two examples each :
(a) Oxidation
(b) Reduction .
Answer:
(a) Oxidation : The reactions in which gain of oxygen takes place are called oxidation.
Examples :
1. 2Cu + O2→ 2CuO
2. 2H2 + O2 → 2H2O

(b) Reduction : The reactions in which loss of oxygen takes place are called reduction.
Examples :

Class-10th-Science-Chapter-1-Reduction-explanation
Class 10th Science Solutions

Question 17.
A shiny brown coloured element X on heating in air becomes black in colour. Name the element X and black coloured compound formed.
Answer:
The shiny brown coloured element X is copper. When it is heated in air, it becomes black due to the deposit of copper oxide.

Class 10th Science Chapter 1 Question 17 Answer
Class 10th Science Solutions

Question 18.
Why do we apply paint on iron articles ?
Answer:
We apply paint on iron, articles to prevent them from corrosion. Paint disconnects the relation between iron and air or water.

Question 19.
Oil and fat containing food items are flushed with nitrogen. Why?
Answer:
Oil and fat containing food items are flushed with nitrogen to prevent them from damage. When such items come in contact of air, they get oxidised and become rancid. Their smell and taste change.

Question 20.
Explain the following terms with an example each :
(a) Corrosion
(b) Rancidity
Answer:
(a) Corrosion : The process of damaging or chemically eaten up the surface of some metals when they are left for some time in moist air is called corrosion.

Conditions of corrosion :
1. Presence of moisture (water)
2. Presence of air
Example : Rusting of iron is a common example of corrosion.

(b) Rancidity : When fats and oils are oxidised, they become rancid and their smell and taste change. This phenomenon is called rancidity.
Example : Fat and oil containing substances are damaged and their taste or smell is changed.

Question 21
Why does the colour of copper sulphate solution change when an iron nail is dipped into it?
Solution:
In this reaction, iron displaces copper from copper sulphate solution. The deep blue colour of copper sulphate solution fades due to the formation of light green solution of iron sulphate. A red-brown coating of copper metal is formed on the surface of the iron metal. This displacement reaction occurs because iron is more reactive than copper.

Question 22
Identify the substances that are oxidised and the substances that are reduced in the following reactions.
i. 4Na(s) + O2 (g) → 2Na2O(s)
ii. CuO(s) + H2(g) → Cu(s) + H2O(l)
Solution:
i. 4Na(s) + O2 (g) → 2Na2O(s)
Here oxygen is added to sodium. The addition of oxygen is Called oxidation. So the substance that is oxidized is sodium Na.
ii. CuO(s) + H2(g) → Cu(s) + H2O(l)

In this reaction, copper oxide (CuO) gives the oxygen required for the oxidation of hydrogen; therefore, copper oxide is the oxidizing agent. Hydrogen is responsible for removing oxygen from copper oxide; therefore, hydrogen is the reducing agent here.

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

NCERT Solutions for Class 10 Science Chapter 1 (MCQs) [1 Mark each]

Question 1.
When crystals of lead nitrate are heated strongly in a dry test tube
(a) crystals immediately melt
(b) a brown residue is left
(c) white fumes appear in the test tube
(d) a yellow residue is left
Answer:
(b)Pungent smelling, brown fumes are evolved due to NO2 gas and brown coloured residue of lead oxide (PbO) is left.

2Pb(NO3)2(s)≜→ 2ObO(s) +4NO2(g) +O2(g)(1)

Question 2.
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? [NCERT Exemplar]
(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 the presence of FeSO4 to a colourless compound
Answer:
(a)Potassium permanganate (KMnO4) in the presence of dil. H2SO4, i.e. in acidic medium, acts as a strong oxidising agent. In acidic medium, KMnO4 oxidises ferrous sulphate to ferric sulphate.

NCERT Solutions

Question 3.
Dilute hydrochloric acid is added to granulated zinc taken in a test tube. The following observations are recorded. Point out the correct observation.
(a) The surface of metal becomes shining
(b) The reaction mixture turns milky
(c) Odour of a pungent smelling gas is recorded
(d) A colourless and odourless gas is evolved
Answer:
(d)Zinc metal reacts with dil. HCl to form zinc chloride and bubbles of colourless and odourless hydrogen gas is evolved.

NCERT Solutions

Question 4.
When a magnesium ribbon is burnt in air, the ash formed is
(a) black
(b) white
(c) yellow
(d) pink
Answer:
(b)When a Mg ribbon is burnt in air, the ash formed is of magnesium oxide which is white in colour.
2Mg(r) + O2(g) → 2MgO(f)

Question 5.
Three beakers labelled as A, B and C each containing 25 mL of water were taken. A small amount of NaOH, anhyd. 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 statements 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, the exothermic process has occurred.
IV. In beaker C, endothermic process has occurred. [NCERT Exemplar]
(a) Only I
(b) Only II
(c) I and IV
(d) II and III
Answer:
(c)As in case of beakers A and B, heat is given out, so temperature became high, hence it is an exothermic reaction while in beaker C, heat is absorbed from water, so temperature falls, hence it is an endothermic process.

Question 6.
Which of the following will be required to identify the gas evolved when dilute hydrochloric acid reacts with zinc metal?
(a) Red litmus paper
(b) pH paper
(c) Lime water
(d) A burning splinter
Answer:
(d)On reacting with dil. HCl, zinc metal forms zinc chloride and hydrogen gas is evolved. Presence of hydrogen gas can be checked by a burning splinter because Hgas burnt in a splinter with a pop sound.

NCERT Solutions

Question 7.
On immersing an iron nail in CuSO4 solution for few minutes, you will observe that
(a) no reaction takes place
(b) the colour of solution fades away
(c) the surface of iron nails acquire a black coating
(d) the colour of solution changes to green
Answer:
(b)Fe(s) + CuSO(aq) → FeSO(aq) + Cu(s)
Fe is present above in the reactivity series of metals. Hence, Fe displaces Cu from CuSO4 solution. And the colour of the solution fades away. This is an example of displacement reaction.

Question 8.
What happens when ferrous sulphate crystals are heated? [CCE 2014]
(a) A gas having the smell of burning sulphur is evolved
(b) No gas is evolved
(c) Brown coloured gas is evolved
(d) Colourless and odourless gas is evolved
Answer:
(a)The green colour of ferrous sulphate crystals changes to brownish black ferric oxide and smell of burning sulphur is evolved due to SO2 and SO3.

NCERT Solutions

Question 9.
The colour of the precipitate formed when barium chloride solution is mixed with sodium sulphate solution is [CCE 2014]
(a) blue
(b) black
(c) white
(d) green
Answer:
(c)This is an example of a double displacement reaction and a white precipitate of barium sulphate is formed.

NCERT SOlutions

Question 10.
How the colour changes when the gases after thermal decomposition of ferrous sulphate come in contact with an acidified solution of potassium dichromate?
(a) Green to orange
(b) Red to colorless
(c) Orange to green
(d) Blue to green

Answer:
(c) The color changes from orange to green due to the formation of iron (III) sulphate

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