INTEXT QUESTION || Class 10 Science : Chapter 1: Chemical Reaction and Equations All Question Answers

INTEXT Question Answers

Page No – 6

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

Ans:- Magnesium is very  reactive metal like ( Na,Ca etc.). when we kept in air for a long time it reacts with oxygen to form a layer magnesium oxide ( MgO) on its surface. Mg(magnesium) + O₂(oxygen) –>2MgO(magnesium oxide)

This layer of magnesium oxide is quite stable and prevents further reaction of magnesium with oxygen . This magnesium ribbon is cleaned by sand paper to remove this layer so that the underlaying metal can be used for the reaction.

Class 10 Science : Chapter 1: Chemical Reaction and Equations All Question Answers

2. Write the balanced equation for the following chemical reactions;

i. Hydrogen + Chlorine ——> Hydrogen Chloride

ii. Barium Chloride + Alluminium Sulphate —–> Barium Sulphate + Alluminium Chloride

iii. Sodium + Water —–> Sodium Hydroxide + Hydrogen 

Ans:- H₂ + Cl₂ —-> HCL

Balanced equation : H₂ + Cl₂ —-> 2HCL

BaCl₂+ Al₂(SO₄)₃ —–> BaSO₄ + AlCl₃

_{Balanced equation :  3BaCl2+ Al2(SO4)3 —–>3BaSO4 + 2AlCl3}

Na + H₂O—–> NaOH + H₂

_{Balanced equation : 2Na +2 H2O—–>2 NaOH + H2}

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

1. Solutions of Barium Chloride and sodium sulphate in water reacts 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 in water

1. BaCl₂ (aq) + Na₂SO₄ (aq) —–> BaSO₄(ppt) + 2NaCl(aq)
2. NaOH(aq) + HCL(aq)——>NaCl (aq) + H₂O(l)

Class 10 Science : Chapter 1: Chemical Reaction and Equations All Question Answers

PAGE NO: 10

1. A solution of a substance X is used for white washing .

 

1. Name the substance X and write its formula.
2. Write the reaction of the substance X named in (i) above the water.

Ans :

 

1. X is a quick lime,CaO
2. CaO (s)  (quick lime) + H₂O(l) ——> Ca(OH)₂(aq)  (Slaked lime or calcium hydroxide)

 

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 the gas.

Ans: It is because water is formed when hydrogen and oxygen combine in the ratio of 2:1 by volume, the gas with double volume is hydrogen . Two atoms of hydrogen combine with one atom of oxygen to form water.Hence ,volume of hydrogen is double.

Class 10 Science : Chapter 1: Chemical Reaction and Equations All Question Answers

 

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Class 10 Science : Chapter 1: Chemical Reaction and Equations All Question Answers

PAGE NO. 13

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

Ans: When an iron nail is dipped in copper sulphate solution , it becomes brownish in colour and the colour of the copper sulphate fades due to the following reactions :

Fe(s) + CuSO₄ (aq) ——-> FeSO₄(aq) + Cu(s)

In this reaction , iron has replaced copper from its solution .

Thus amount of copper sulphate decrease and its colour fades.

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

Ans: When a solution of hydrochloric acid is added to a solution of lead nitrate , a white

precipitate of lead chloride is found .

Pb(NO₃)₂ (aq) + 2HCL (aq) ——> PbCl(s) ( lead chloride) + 2HNO₃(aq)(nitric acid)

Pb²⁺ ions form lead nitrate combine with 2Cl^– ions from hydrochloric acid and a precipitate of lead chloride is formed . Thus, there is a exchange of ions between the two reactants i.e lead nitrate and hydrochloric acid and thus this reaction is a double displacement reaction.

3. Identify the substances 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

Ans

1.  Sodium metal is oxidized and oxygen is reduced to Na₂O.
2. Copper oxide is reduced to copper and hydrogen is oxidized to H₂O

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EXERCISE || Class 10 Science : Chapter 1: Chemical Reaction and Equations All Question Answers

 

 

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

2PbO (s) + C (s) ——-> 2Pb(s) + CO2 (g)

1. Lead is getting reduced.
2. Carbon dioxide is getting oxidized.
3. Carbon is getting oxidized.
4. Lead oxide is getting reduced.

1. (a) and (b)
2. (a) and (c)
3. (a) ,(b) and (c)
4. all

Ans: (i) (a) and (b)

 

2.  Fe2O3 + 2Al —–> Al2O3+ 2Fe

The above reaction is an example of a 

 

1. combination reaction
2. double displacement reaction
3. decomposition reaction
4. displacement reaction

Ans: (d) Displacement reaction

 

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

 

1. Hydrogen gas and iron chloride are produced
2. chlorine gas and iron hydroxide are produced
3. no reaction takes place
4. iron salt and water are produced.

 

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

 

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

Ans: In a balanced equation , the number of atoms of each elements on both sides of the equation are equal. The balanced equation satisfied mass balance as well as charge balance.

The chemical equation must be balanced with respect to mass because matter can neither be created nor be destroyed.

The equation must be balanced with respect to charge because the electrons lost by atoms to form cations are equal to the electrons gained by other atoms to form anions.

Class 10 Science : Chapter 1: Chemical Reaction and Equations All Question Answers

5. Translate the following statements into chemical equations and then balance them.

1. Hydrogen gas combines with nitrogen to form ammonia.
2. Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
3. Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
4. Potassium metal reacts with water to give potassium hydroxide and hydrogen gas is released.

Ans:

1.  3 H₂ (g) + Na₂(g) ——> 2NH₃(g)
2. 3H₂S (g) + 3O₂(g) ——-> 2H₂O (l)+  2SO₂(g)
3. 3BaCl₂(aq) + Al(SO₄)₃(aq)——-> 2AlCl₃(aq) + 3BaSO₄(s)
4. 2K(s) + 2 H₂O(l) ——-> 2KOH + H₂(g) (released)

 

6. Balance the following chemical  equations.

1. HNO₃ + Ca(OH)₂ ——> Ca(NO₃)₂ + H2O
2. NaOH + H₂SO₄——–> Na₂SO₄ + H₂O
3. NaCl + AgNO₃ ——-> AgCl + NaNO₃
4. BaCl₂ + H₂SO₄ ——> BaSO₄ + HCl

Class 10 Science : Chapter 1: Chemical Reaction and Equations All Question Answers

Ans:

1. 2HNO_{3 ^(aq)}+ Ca(OH)_2^(aq)——> Ca(NO₃)₂ (aq)+ 2H2O(l)
2. 2NaOH (aq)+ H₂SO_4^(aq)——–> Na₂SO_4^(aq) + H₂O(l)
3. NaCl (aq)+ AgNO_3^(aq) ——-> AgCl(s) + NaNO_3^(aq)
4. BaCl_2^(aq) + H₂SO_4^(aq) ——> BaSO_4^(s) + 2HCl(aq)

7. Write the balanced chemical equations fo the  following reactions .

1. Calcium hydroxide + carbon dioxide ———> calcium carbonate + Water 
2. zinc + silver nitrate ———> Zinc nitrate + Silver 
3. Aluminium + Copper Chloride ——–> Aluminium Chloride + copper
4. Barium Chloride + Potassium sulphate ——–> Barium sulphate + potassium chloride

 

Ans :

1. Ca(OH)2 + CO2 (g) ——–> CaCO3(s) + H2O
2. Zn(s) + 2AgNO3 (aq)——–> ZnNO3 (aq) + 2Ag(s)
3. 2Al (s) + 3CuCl2(aq) ———> 2 AlCl3 (aq) + 3 Cu(s)
4. BaCl2(s) + K2SO4 ( aq) ——> BaSO4(s) + 2 KCl(aq)

8. Write the balanced chemical equation for the followimg and identify the type of reaction in each case.

1.  Potassium Bromide (aq)+  Barium iodide(aq) ——–> potassium iodide (aq) + Barium bromide
2. Zinc  carbonate(s) ——–> zinc oxide (s) + Carbon dioxide(g)
3. Hydrogen(g) + Chlorine (g) ——–> Hydrogen chloride(g)
4. Magnesium (s) + hydrochloric acid (aq) —-> Magnesium chloride (aq) + Hydrogen(g)

 

Ans:

 

1. 2KBr(aq) + BaI₂(aq) ——> 2KI (aq) + BaBr₂(s)
2. ZnCO₃(s) —–> ZnO (s) + CO₂(g)
3. H₂(g) +Cl₂(g) —–> 2HCl(g)
4. Mg(s) + 2HCl(aq) —–> MgCl₂(aq) + H₂(g)

Class 10 Science : Chapter 1: Chemical Reaction and Equations All Question Answers

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

Ans: (i)Exothermic reaction :

Chemical reaction in which energy is envolved (or given out) are known as Exothermic reaction. For example :

C(s) + O₂ (g) ——-> CO₂(g) + Δ H

Formation of ammonia from nitrogen and Hydrogen is an exothermic reaction.

N₂ (g) 3H₂(g) ——-> 2 NH₃ (g) + 92 kJ

 

(ii) Endothermic reaction : Reaction in which energy is absorbed are called endothermic reaction . For example :

When carbon reacts with sulphur 92 KJ of heat is absorbed during the process.

C(s) + 2S(s) ——> CS2(l) – 92 KJ

 

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

Ans: During digestion, food is broken down into simpler substances . Food like rice , potato and  bread are made up of carbohydrates are further  broken down to  glucose . glucose during respiration ( inhalation of oxygen ) is oxidized with the liberation of energy as shown below :

C₆H₁₂O₆(aq) [glucose] + O₂(aq) ——> CO₂(aq)  + 6H₂O (l) + energy

Thus , respiration is an exothermic reaction.

Class 10 Science : Chapter 1: Chemical Reaction and Equations All Question Answers

11. Why are decomposition reactions called the opposite of combination reaction ? write equations for these reactions.

Ans: The decomposition reaction is the opposite of combination reaction .

In a decomposition reaction , a single compound breaks down to produce two or more simpler substances. E.g. Mercuric oxide on heating decomposes to mercury and oxygen .

2HgO —(heat)—–>2Hg + O₂

In a combination reaction , two or more substances simply combine to form a new substance .

E.g. -> Magnesium combine with oxygen to give magnesium oxide .

2 Mg + O_2-—-> 2MgO

Class 10 Science : Chapter 1: Chemical Reaction and Equations All Question Answers

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

Ans : Heat —–>  CaCO₃ (s) —(heat)—> CaO (s) + CO₂(g)

Light ——> 2AgBr(s) —-(sunlight)—> 2Ag + Br₂(g)

Electricity —–> 2 H₂O (l) —-(electric current)—–> 2H₂(g) + O₂(g)

13. What is the difference between displacement and double displacement reactions?

Ans: In displacement reaction, a more reactive metal displaces a less reactive  metal from its solution while in double displacement reactions, two or more compounds exchange  their ions and form new compounds .

(i) Fe(s) + CuSO₄(aq) —–> Cu(s) +FeSO₄(aq)

This is a displacement reaction where iron displace copper from its solution .

(ii) AgNO₃ (aq) + NaCl (aq) —–> AgCl (s) + NaNO₃

This is a double displacement reaction where silver  nitrate and sodium chloride exchange Cl and NO3 ions between them.

Class 10 Science : Chapter 1: Chemical Reaction and Equations All Question Answers

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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 : 2AgNO₃ (aq) + Cu(s) ——-> Cu(NO₃)₂ (aq)+ 2Ag(s)

 

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

Ans: When two reactants in solution react and one or more of the products is insoluble or forms a precipitate the reaction is called a precipitation reaction . For example , when a solution of iron chloride and ammonium hydroxide are mixed , a brown precipitate of iron hydroxide is formed

FeCl₂(aq) + 3 NH₄OH(aq) ——–> Fe(OH)₃ (s) + 3 NH₄Cl(aq)

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

(a) Oxidation (b) Reduction

 

Ans:(a) Oxidation : A chemical reaction in which a substance gains oxygen and losses hydrogen  is called oxidation.

Example : 2Mg (s) + O2(g) [burning ]——> 2 MgO (s)

Mg is oxidized to MgO

(b) Reduction : A chemical reaction in which  a substance losses oxygen and gains hydrogen is called Reduction.

Example : CuO (s) + H2(g) [heat]——> Cu(s) + H2O (g)

CuO is reduced to form Cu.

 

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

Ans: Element ‘X’ = copper (Cu)

Compound = copper Oxide (CuO)

2 Cu (s) [brown]+ O₂ (g)—-(heat)–> 2CuO (s) [black]

Class 10 Science : Chapter 1: Chemical Reaction and Equations All Question Answers

18. Why do we apply paint on iron articles? 

Ans: Paint acts as anti oxidant saves iron articles from damage due to corrosion . It acts as buffer between iron articles and moisture.

 

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

Ans : To keep food items fresh and save these from oxidizing effect of oxygen , food items are flushed with nitrogen.

 

20. Explain the following terms with one example each.

(a) Corrosion (b) Rancidity

 

Ans: (a) Corrosion :  Due to the effect of moisture and oxygen metals get corroded . i.e metals particularly iron forms a porous layer on the surface and thus gets damaged . The effect is called corrosion .

Corrosion causes damages to metal articles like car bodies , bridges , iron railings , ships, and other substances of daily use.

 

(b) Rancidity : Fats and oils in food kept for long time get oxidized and become rancid and taste of food changes and causes infection on eating . This is called rancidity.

To prevent rancidity antioxidants are added to foods containing fats and oils. Rancidity can also be prevented by flushing to oxygen with an inert gas like nitrogen . For example, packets of food items like chips are flushed with nitrogen so that these can be used even afṭer long duration.

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Class 10 Science : Chapter 1: Chemical Reaction and Equations All Question Answers