Class 10 Science Chapter 1 Pdf Question Answer

Here you will find class 10 science chapter 1 pdf question answer belongs to NCERT Class 10 Science Chapter 1 Chemical Reactions and Equations that will help the students of class 10 to understand concepts. Class 10 Science Solutions Chapter 1 in Hindi will be useful for Hindi medium students.

The students can download NCERT Solutions for Class10 Science Chapter 1 Chemical Reactions and Equations in PDF format for offline use. You can also go through Activity 1.1 based on the chapter.

You must know the topics and subtopic of Chapter 1 Chemical Reactions and Equations of NCERT Science for Class 10 before you go through the NCERT Solutions for Class10 Science Chapter 1 Chemical Reactions and Equations

1. Chemical Reactions and Equations

2. Chemical Equations

3. Types of Chemical Reactions

4. Have You Observed The Effects of Oxidations Reactions in Everyday Life?

Students of CBSE board, RBSE and other state boards of Rajasthan, Uttar Pradesh, M.P., Gujrat and all other states can download NCERT Solutions for Class10 Science Chapter 1 Chemical Reactions and Equations in English medium and Hindi medium in PDF format for free.

NCERT Solutions for Class10 Science Chapter 1 Chemical Reactions and Equations

Chemical reaction and equations

After reading and studying the NCERT solution of Chapter 1 Chemical Reactions and Equations class 10, you will be able to answer the following questions and enhance your knowledge about the chapter more effectively.

1. Types of reactions

2. What are 4 types of chemical reactions?

3. What are the 5 major types of chemical reactions?

4. What is a chemical reaction and give one example?

5. How do you balance chemical equations?

6. What is combination reactions?

7. What is precipitation reactions?

8. What is a double displacement reaction, give an example?

9. How to balance a chemical equation?

10. What is the difference between a chemical reaction and an equation?

TEXTBOOK QUESTIONS:

Questions (Page 6)

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

Ans. Magnesium ribbon should be cleaned before burning to remove the layer of Magnesium oxide [MgO] over its surface because it reacts with atmospheric Oxygen and forms Magnesium oxide. Magnesium oxide [MgO] does not allow Magnesium to burn

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

(i)Hydrogen + Chloride→HydrogenChloride

(ii)Barium chloride+Aluminium sulphate→Barium sulphate +Aluminium chloride

(iii)Sodium +water→Sodium hydroxide+ Hydrogen

Ans.

(i)H₂+ Cl₂→2HCl

(ii)3BaCl₂+Al₂Cl₃→3BaSO₄+2AlCl₃

(iii)2Na+2H₂O→2NaOH+H₂

Q.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 sodium chloride.

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

Ans. Balanced chemical equations with state symbols for the reactions are as follows:

(i)BaCl_2(aq) +Na₂SO_4(aq) →BaSO_4(aq)+ NaCl_(aq)

(ii) NaOH_(aq)+HCl_(aq)→NaCl_(aq)+H₂O

Questions (Page 10)

Q.1A 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.

Ans.

(i)In whitewashing the wall a solution of quick lime is used. so substance ‘X’ is quick lime and its formula is CaO.

(ii) Substance ‘X’ [CaO] reacts with water to form calcium hydroxide (slaked lime).

CaO_(s) + H₂O→Ca(OH)₂

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

Ans. Water (H₂O) contains two parts hydrogen and one part oxygen During electrolysis of water, on passing current water decomposes to form hydrogen and oxygen gases. The amount of hydrogen and oxygen produced during the electrolysis of water is in a 2:1 ratio.

`H_2O_{(l)} \overset\text{ Electrolysis }{\rightarrow} 2H_{2(g)} + O_{2(g)}`

In the above reaction, the balanced equation shows that during electrolysis of water, 1 mole of oxygen gas and 2 moles of hydrogen gas are produced. That’s why the amount of gas is double in one of the test tubes and it is hydrogen gas.

Questions (Page 13)

Q. 1 Why does the colour of copper sulphate solution change, when an iron nail is dipped in it?

Ans. Iron is a more active element than copper. The copper sulphate (CuSO₄) solution is of blue colour, Iron (Fe) displaces copper from its compound copper sulphate (CuSO₄) and changes to iron sulphate (FeSO₄) which is green in colour. That’s why the blue colour of the copper sulphate solution changed.

Fe+CuSO₄→FeSO₄ +Cu

Q.2Give an example of a double displacement reaction other than the one given in above activity 1.10

Ans. The other example of a double displacement reaction is – the mixing of solutions of sodium carbonate and calcium chloride and in this reaction calcium carbonate and sodium chloride is formed.

Na₂CO_3(aq)+CaCl_2(aq) → CaCO_3(s)+2NaCl_(aq)

Q.3Identify the substances oxidized and the substances reduced in the following reactions:

(i)4Na_(s)+ O_2(g) →2Na₂O_(s)

(ii)CuO_(s) +H₂→Cu+H₂O

Ans.

i). Sodium gains oxygen so it gets oxidized and on the other hand, oxygen gets reduced.

(ii)Copper oxide is reduced to copper and hydrogen gets oxide to water.

Reaction

Substance oxidised

Substance reduced

(i)

(ii)

H₂

O₂

CuO

EXERCISES:

Q.1 Which of the statements about the reaction below are incorrect?

2PbO_(s)+C_(s) →2Pb_(s)+CO_2(g)

(a)Lead is getting reduced.

(b)Carbon dioxide is getting oxidised.

(d)Lead oxide is getting reduced.

(i) a and b (ii) a and c

(iii) a, b and c (iv) all.

Ans. (i) a and b.

Q.2 Fe₂O₃ +2Al→Al₂O₃+2Fe

The above reaction is an example of

(a) Combination reaction

(b) Double displacement reaction

(d) Displacement reaction

Ans. (d)Displacement reaction

Q. 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

(d) Iron salt and water are produced

Ans. (a) Hydrogen gas and iron chloride are produced.

Fe_(s)+dil2HCl_(aq)→FeCl_2(aq)+H₂↑

Q.4 What is a balanced chemical equation? Why should the chemical equation be balanced?

Ans. A reaction in which the number of atoms of all the elements on both sides of the chemical equation is equal is called a balanced chemical equation. According to the law of conservation of mass states that mass can neither be created nor destroyed. So the total mass of reactants should be equal to the total mass of the products. That’s why the total number of atoms of each element should be equal on both sides of a chemical equation. That’s why chemical equations should be balanced.

Q.5Translate 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 the air to give water and sulphur dioxide.

(d)Potassium the metal reacts with water to give potassium hydroxide and hydrogen ga

Ans.

(i)N_2(g)+H_2(g)→2NH_3(g)

(ii)H₂S_(g)+3O_2(g) →2H₂O_(l)+S)_2(g)

(iii)3BaCl_2(s)+Al₂(SO₄)_3(aq)+3BaSO₄↓

(iv)2K_(s)+2H₂O_(l)→2KOH_(l)+H_2(g)

Q.6 Balance the following chemical equations:

(i)HNO₃+Ca(OH)₂→Ca(NO₃)₂+H₂O

(ii)NaOH+H₂SO₄→Na₂SO4+H₂O

(iii)NaCl+AgNO₃→BaSO₄+HCl

(iv)BaCl₂+H₂SO₄→BaSO₄+HCl

Ans.

(i)2HNO₃+Ca(OH)₂→Ca(NO₃)₂+2H₂O

(ii)2NaOH+H₂SO₄→Na₂SO4+2H₂O

(iii)NaCl+AgNO₃→BaSO₄+HCl

(iv)BaCl₂+H₂SO₄→BaSO₄+2HCl

Q.7 Write the balanced chemical equations for the following reactions:

(a)Calcium hydroxide +Carbon di oxide→ Calcium carbonate +water

(b)Zinc+ Silver nitrate →Zinc nitrate +Silver

(d)Barium chloride +Potassium sulphate →Barium sulphate potassium chloride

Ans.

a)Ca(OH)₂+CO₂ →CaCO₃H₂O

(b)Zn +2AgNO₃→ZnNO₃+2Ag

(d)BaCl₂+K₂SO₄→ BaSO₄+2KCl

Q.8 Write the balanced chemical equations for the following reactions and identify the type of reaction:

(a)Potassium bromide(aq)+Barium iodide(aq)→Potssium iodide(aq)+Barium bromide(aq)

(b)Zinc carbonate→(s)Zinc oxide(s)+Carbon dioxide(g)

(d)Magnesium(s)+Hydrochloric acid(aq) →Magnesium chloride(aq)+Hydrogen(g)

Ans.

(a)2KBr_(aq)+BaI_2(aq)→2KI_(aq)BaBr_2(aq)

(b)ZnCO_3(s)→ZnO_(s)+CO_2(g)

(c)H_2(g)+Cl_2(g)→2HCl_(g)

(d)Mg_(s)+HCl_(aq) →MgCl_2(aq)+H_2(g)

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

Ans.

Exothermic reaction- A chemical reaction in which energy is released in the form of heat is called an exothermic reaction.

C + O₂ → CO₂ +395kJ

CH₄ +2O₂ →CO₂ +2H₂O +890kJ

Endothermic reaction - A chemical reaction in which energy is absorbed or gained i is called an endothermic reaction.

N₂ + O₂ +180.5kJ →2NO

Q.10 Why is respiration considered as an exothermic reaction? Explain.

Ans. Energy is essential for different life processes and this energy is obtained from the food that we eat. During digestion, large molecules of food are broken down into simpler substances such as glucose. Glucose combines with oxygen in the cells and in this process, energy is released. The name of this reaction is respiration. Since energy is released in the whole process, it is an exothermic process.

`C_6H_12O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text {energy}`

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

Ans. In a combination reaction, two or more substances (elements and compounds) combine to form a single substance, whereas in a decomposition reaction, one substance (compound) changes to two or more simpler substances (elements or compounds). That’s why; a decomposition reaction is called the opposite of a combination reaction.

Combination reaction

`2H_2 + O_2 \rightarrow 2H_2O`

Decompostion reaction

`2H_2O \overset\text{electric current}{\rightarrow}2H_2 + O_2`

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

Ans. For decomposition reaction, energy is required in the form of heat, light or electric current.

(i)Decomposition of limestone (Calcium Carbonate) into lime (calcium oxide) and carbon dioxide is carried out by supplying heat.

`CaCO_3 \overset\text{heat}{\rightarrow}CaO +CO_2`

(ii)Decomposition of silver bromide into silver and bromine takes place on exposure to light.

`2AgBr \overset\text{light}{\rightarrow} 2Ag Br`

(iii)Decomposition of water in hydrogen and oxygen gases takes place by supplying electricity.

`H_2O_{(l)} \overset\text{Electric current}{\rightarrow} 2H_{2(g)} + O_{2(g)}`

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

Ans.Displacement reaction- a more reactive element replaces a less reactive element from a compound.

`Zn+ 2AgNO_3 \rightarrow ZnNO_3 + 2Ag`

`Zn+ CuSO_4 \rightarrow ZnSO_4+ Cu`

Double Displacement reaction

`CuCl_2 + AgNO_3 \rightarrow 2AgCl + Cu(NO_3)_2`

`BaCl_2 + K_2SO_4 \rightarrow BaSO_4 + 2KCl`

Q.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. In the refining of silver from silver nitrate solution by copper metal, the reaction is as follows:

`Cu + 2AgNO_3 \rightarrow Cu(NO_3)_2 + 2Ag`

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

Ans. A reaction in which an insoluble solid substance is formed, is called a precipitate and the reaction is called a precipitation reaction.

`BaCl_2 + Na_2SO_4 \rightarrow BaSO_4 + 2NaCl`

Q.16 Explain the following in terms of gain or loss of oxygen with two examples each:

(a) Oxidation (b) reduction

Ans.

Oxidation reaction

`C+ O_2 \rightarrow CO_2`

`2Mg + O_2\rightarrow 2MgO`

Reduction reaction

`2H_2O \rightarrow 2H_2 + O_2`

`2MgO \rightarrow 2Mg + O_2`

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

Ans. When air is passed over heated copper powder, it reacts with oxygen in the air to form copper (II) oxide which is black in colour.

`2Cu+O2\rightarrow 2CuO`

Element ‘X’ is copper and the black-coloured compound is copper (II) oxide

Q.18 Why do we apply paint on iron articles?

Ans. For rusting of iron articles, their open surface, oxygen and moisture are essentially required. Applying paint, the surface is covered and moreover, oxygen of the air is not in contact with the surface of the metal. Iron articles get rusted when coming in contact with air and moisture but when they are painted, the contact of iron articles from moisture and air is cut off. Hence, rusting is prevented.

Q.19 Oil and fat-containing food items are flushed with nitrogen. Why?

Ans. When food items are kept open and unprotected for some time, they give an unpleasant smell and taste of becoming rancid, this process is called rancidity. This happens because of the oxidation of food items. Nitrogen is an inert gas and does not easily react with these substances. That’s why bags used in packing food items are flushed with nitrogen gas to remove oxygen inside the pack.

Q.20 Explain the following terms with an example each:

(a) Corrosion (b) rancidity

Ans. (a). Corrosion is defined as a process where materials, usually metals, deteriorate as a result of a chemical reaction with air, moisture, chemicals, etc.

Eg. - In the presence of moisture, Iron reacts with oxygen to form hydrated iron oxide.

`4Fe+ 3O_2 +nH_2O \rightarrow 2Fe_2O_3.nH_2O`

This hydrated iron oxide is rust.

(b). Rancidity - The process of oxidation of fats and oils containing food items and their smell and taste get changed, this process is known as rancidity. For example - The taste and smell of butter change when kept for long.

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