Class 10 Science Chapter 1 Previous Years Board Questions

Class 10 Science Chapter 1 Board Questions of Chemical Reactions and Equations for the preparation of session 2020-21 CBSE exams. This collection of questions includes CBSE previous years board questions, Class 10 Science Chapter 1 last 10 years paper’s questions with answers.

Questions are categories according to 1 mark, 2 marks, 3 marks and 5 marks questions. More questions will be added as per the requirement of the users and need of the session 2020-2021.

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Class 10 Science Chapter 1 Board Questions Previous Years

Class:10
Subject:Science
Contents:Previous Years Board Questions

Class 10 Science Chapter 1 Previous Years Questions

Class 10 Science Chapter 1 Previous Years Board Questions from CBSE Papers are given below for the preparation of CBSE Exams 2020-21. Questions are categories in sets of 3 marks, 5 marks, 2 marks or 1 marks. So, that students can set the length of the answers. Answers of the each question is also given, taken from NCERT Books of Class 10 Science.

10th Science Chapter 1 Board Questions Set – 1 (3 Marks)

A reddish brown coloured metal, used in electrical wires, when powdered and heated strongly in an open china dish its colour turns blacks. When hydrogen gas is passed over this black substance, it regains its original colour. Based on above information answer the following question. (i) Name the metal and the black coloured substance formed. (ii) Write balanced chemical equation for both the equation. [CBSE 2012]

(i) Reddish brown metal is copper. When it is heated in china dish presence of oxygen, black coloured copper oxidised is formed.

(ii) 2Cu + O2 → 2CuO

When hydrogen gas is passed over heated copper oxide reddish brown copper metal is formed.

CuO + H2 → Cu + H2O

What is redox reaction? Identifying the substance oxidised and the substance reduced in the following reactions: (i) 2PbO + C → Pb + Co2 (ii) MnO2 + 4HCL → MnCl2 + H2O + Cl2. [CBSE 2012]

Those reactions in which oxidation and reduction take place simultaneously are called redox reaction.
(i) Pbo is getting reduced and C is getting oxidised.
(ii) MnO2 is getting reduced. HCL is getting oxidised.

What is rancidity? Mention any two ways by which rancidity can be prevented. [CBSE 2012]

The process in which taste and smell of food gets spoiled is called rancidity. It happens due to oxidation.
Prevention from rancidity:
(i) Antioxidants are added to fatty acid to prevent oxidation e.g. chips are packed in the presence of Nitrogen gas which prevents spoilage by oxidation.
(ii) Food should be kept in airtight container in refrigerator.

Write balanced chemical equation for the reaction that take place during respiration. Identifying the type of combination reaction that take place during this process and justifying the name. Give one more example of this type of reaction. [CBSE 2012]

C6H12O6 + 6O2 → 6Co2 + 6H2O + heat
It is exothermic combination reaction because heat is being evolved.
CH4 + 2O2 → CO2 + 2H2O
Combustion of methane is another example of exothermic combination reaction.

Double Displacement Reaction

A chemical reaction in which there is an exchange of ions between the reactants to give new substances is called a double displacement reaction.




10th Science Chapter 1 Board Questions Set – 2 (3 Marks)

What is meant by: (i) Displacement reaction (ii) Reduction reaction (iii) Combination reaction. Write balanced chemical equation for each reaction. [CBSE 2012, 2011]

(i) Those reactions in which a more active element displaces a less active element from its compound are called displacement reaction.
Example: Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s
(ii) The reaction in which hydrogen is added or oxygen is removed or gain of electrons take place.
Example: Fe+3 + e– → Fe+2
(iii) The reaction in which two or more element or compound combine together to form a single compound are called Combination reaction.
Example: C(s) + O2(g) → CO2(g)

(a) Why is respiration consider as exothermic reaction? (b) Define the terms Oxidation and reduction? (c) Identify the substance that is oxidised and reduced in the reaction: CuO + Zn → Cu + ZnO. [CBSE 2011]

(a) It is because heat is evolved during respiration.

(b) Oxidation is a process in which O2 or H2 is removed or loss of electron take place reduction is a process in which hydrogen is added or oxygen is removed or gain of electron take place.

(c) Zn is getting oxidised, CuO is getting reduced.

2g of lid nitrate powder is taken in a boiling tube. The boiling tube is heated over a flame now answer the following: (i) State the colour of the fumes evolved and the residue left. (ii) Name the type of chemical reaction that has taken place stating its balanced chemical equation. [CBSE 2012]

(i) Brown coloured fumes of No2 gas are evolved and yellowish brown reside is formed.

(ii) Decomposition reaction has taken place as,
2Pb(NO3)2 → 2PbO + 4NO2 +O2

(i) Classsify the following reaction into different type: (a) AgNO3 + NaCl → AgCl + NaNO3 (b) CaO + H2O → Ca(OH)2 (c) 2KClO3 → 2KCl + 3O2. (ii) Which of the above reaction are precipitation reaction? Why is a reaction called precipitation reaction? [CBSE 2011]

(i)
(a) Precipitation reaction(Double Displacement reaction)
(b) Combination reaction
(c) Decomposition reaction

(ii) It is precipitation reaction because one the product formed is in soluble in water

Reactivity Series

The Reactivity series is a list of metals arranged in the order of decreasing reactivity. The most reactive metal is placed at the top and the least reactive metal is placed at the bottom.

10th Science Chapter 1 Board Questions Set – 3 (3 Marks)

What is meant by: (i) Precipitation reaction (ii) Exothermic reaction (iii) Oxidation reaction. Write balanced chemical equation for an example of each. [CBSE 2011]

(i) The reaction in which two compound exchange their ions and the product formed is insoluble in water is called precipitation reaction.
Example: CuSO4(aq) +H2→Cu+H2So4

(ii) The reaction in which heat is evolved.
Example: C6H12O6 + 6O2 → 6Co2 + 6H2O + heat

(iii) The reaction in which O2 is added or H2 is removed or loss of electron take place.
Example: 2Cu + O2 → 2CuO

In the electrolysis of water: (a) Name the gas collected at the cathode and the anode. (b) Why is the volume of gas collected at one electron is double of the other. (c) Why are a few drops of dil. H2So4 added to the water? [CBSE 2012]

(a) The following gases are collected:
At cathode: Hydrogen and at anode: Oxygen

(ii) H:O = 2:1

(iii) Pure water does not conduct electricity. A few drops of dil. H2So4 are added to make water conducting.

You might have noted that when copper powder is heated in a china dish, the surface of the copper powder becomes coated with a black colour substance. (i) How has this black colour substance formed. (ii) What is that black substance. (iii) Write the chemical equation of the reaction that take place. [CBSE 2011]

(i) Copper reacts with oxygen is to formed Copper Oxide Which is black that is, oxidation of copper take place.

(ii) Copper oxide.

(iii) Cu + O2 → 2CuO

An aqueous solution of metal nitrate ‘P’ reacts with sodium bromide solution to form yellow precipitation compound ‘Q’ which is used in photography. ‘Q’ on exposure to sunlight undergoes decomposition reaction to form metal present in along with a reddish brown gas. Identify ‘P’ and ‘Q’. Write balanced chemical equation for the chemical reaction. List two categories in which this reaction can be placed. [CBSE 2012]

(i) P is silver nitrate, AgNO3.
Q is silver bromide, AgBr.

(ii) AgNO3 + NaBr □(→┴(sunlight ) ) AgBr + NaNO3
2AgBr □(→┴Sunlight ) 2Ag + Br2

(iii) Decomposition of silver bromide can be put under two categories:
(a) Decomposition reaction.
(b) Photochemical reaction

Write balanced chemical equation for the reactions that take place during respiration. Identify the type of combination reaction that takes place during this process and justify the name. Give one more example of this type of reaction. [CBSE 2012]

(i) The carbohydrates that we take in our food are oxidised to carbon dioxide and water.
C6H12O6 + 6O2→ 6CO2 + 6H2O
Carbon of carbohydrate and oxygen combine to form CO2.

(ii) It is an exothermic combination reaction.

(iii) Decomposition of vegetable matter into compost is another example of this type of reaction.

Redox Reaction

A reaction, in which oxidation and reduction takes place simultaneously is known as redox reaction.

10th Science Chapter 1 Board Questions Set – 4 (3 Marks)
Take 3g of barium hydroxide in a test tube, now add amount 2g of ammonium chloride and mix the contents with the help of the glass rod. Now touch the test tube from outside. (i) What do you feel on touching the test tube? (ii) State the inference about the type of reaction occurred. (iii) Write the balanced chemical equation of the reaction involved. [CBSE 2016]

(i) The test tube becomes hot.

(ii) It is a decomposition reaction.

(iii) 2NH4Cl + Ba(OH)2 → BaCl2 + 2NH3 + 2H2O

Name the substance oxidised and reduced, and also identify the oxidising agents and reducing agents in the following reactions: (i) Fe2O3 + 3Co → 2Fe + 3CO2. (ii) 3MnO2 + 4Al → 3Mn + 2Al2O3. (iii) H2S + SO2 → S + H2O. [CBSE 2013]

(i) Fe2O3+3CO→ 2Fe + 3CO2
Fe2O3 is reduced because oxygen has been reduced and CO is oxidised because O has been added to it. Fe2O3 has acted as oxidising agent and CO has acted as reducing agent.

(ii) 3Mno2 +4Al → 3Mn + 2Al2O3
MnO2 is reduced because O has been removed from it to give Mn. Al has been oxidised because O has been added to it to obtain Al2O3. MnO2 is the oxidising agent while Al is reducing agent.

(iii) 2 H2S + SO2→3S +2H2O
H2S has lost H to change into S. Thus, it has been oxidised. SO2 has been lost O to change into S. Thus, it has been reduced. H2S has acted as reducing agent while SO2 has acted as oxidising agent.

Classify the following chemical reactions as exothermic or endothermic: (i) Water is added to quick lime. (ii) Dilute sulphuric acid is added to zinc granules. (iii)When ammonium chloride is dissolved in water in a test tube it becomes cold. (iv) The decomposition of vegetable matter into compost. (v) Electrolysis of water. (vi) Silver chloride turns grey in the presence of sunlight to form silver metal. [CBSE 2016]

(i) Water is added to quick lime — Exothermic

(ii) Dilute sulphuric acid is added to zinc granules – Exothermic

(iii)When ammonium chloride is dissolved in water in a test tube it becomes cold — Endothermic

(iv) The decomposition of vegetable matter into compost — Endothermic

(v) Electrolysis of water – Endothermic

Complete and balance the following equation: (i) NH3 + O2→ (ii) NaOH + H2So4 → (iii) Pb(No3)2 + Kl → [CBSE 2013]

(i) 4NH3 + 5O2→ 4NO + 6H2O

(ii) 2NaOH + H2So4 → Na2So4 + 2H2O

(iii) Pb(No3)2 + 2Kl → PbI2 + 2KNO3

Oxidation of Food Stuff

Potato chips contain oils and fats, which react with atmospheric oxygen and became rancid. To protect chips from oxidation, nitrogen gas is passed through bags of chips which removes air(oxygen) from them. Nitrogen doesn’t react with chips.




10th Science Chapter 1 Board Questions Set – 5 (3 Marks)
You must have tasted or smelt the fat containing food material left for a longtime. Such foods taste and smell bad. What is the reason for this? Name to the phenomenon responsible for it. List two majors for its Preventions. [CBSE 2016]

Food material left for a long time is oxidised by atmospheric oxygen. This changes the smell and taste of food.
Majors for prevention:
(i) Keep the food in air tight container.
(ii) Flush the food packets with nitrogen gas before sealing it.

Name the type of chemical reactions represented by the following equation: (i) CaCo3 □(→┴(heat ) ) CaO + CO2. (ii) CaO + H2O → Ca(OH)2. (iii) Zn + H2So4→ ZnSO4 + H2. [CBSE 2017]

(i) CaCo3 □(→┴(heat ) ) CaO + CO2
This is a decomposition reaction.

(ii) CaO + H2O → Ca(OH)2
This is a combination reaction.

(iii) Zn + H2So4→ ZnSO4 + H2
This is a displacement reaction.

Write chemical equation for the reaction taking place when: (i) Mangnesium react dil. HNO3. (ii) Sodium react with water. (iii) Zinc react with hydrochloric acid. [CBSE 2016]

(i) Mg + 2HNO3(dil) → Mg(NO3)2 +H2

(ii) 2Na + 2H2O → 2NaOH + H2

(iii) Zn + 2HCL→ ZnCl2 + H2

Classify the following chemical reactions as exothermic or endothermic: (i) Water is added to quick lime. (ii) Dilute sulphuric acid is added to zinc granules. (iii)When ammonium chloride is dissolved in water in a test tube it becomes cold. (iv) The decomposition of vegetable matter into compost. (v) Electrolysis of water. (vi) Silver chloride turns grey in the presence of sunlight to form silver metal. [CBSE 2017]

(i) Water is added to quick lime — Exothermic

(ii) Dilute sulphuric acid is added to zinc granules – Exothermic

(iii)When ammonium chloride is dissolved in water in a test tube it becomes cold — Endothermic

(iv) The decomposition of vegetable matter into compost — Endothermic

(v) Electrolysis of water – Endothermic

Decomposition reaction require energy either in the form of heat or light or electricity for breaking down down the reactants. Write one equation each for decomposition reaction where energy is supplied in the form of heat, light and electicity. [CBSE 2018]

Energy supplied in the form of heat:
Ca(OH)2(aq) → CaO(s) + H2O(l)

Energy supplied in the form of light:
2AgCl(s) → 2Ag(s) + Cl2

Energy supplied in the form of electricity:
2H2O→2H2+O2

Following questions are of five marks. Answers are confined to NCERT Books of Class 10 Science and CBSE Sample Papers of last 10 years papers.

10th Science Chapter 1 Board Questions Set – 6 (5 Marks)
(a) Can we stir silver nitrate solution with a copper spoon? Why or why not? Support you answer. (b) Why a brown coating is formed on the iron rod when iron rod is kept dipped in copper sulphate solution for some time? What change will be observed in the colour of the solution. (c) A green coating develops on the copper vessel in the rainy season. Why? [CBSE 2015]

(a) We cannot stir silver nitrate with a copper spoon. Copper being more reactive than silver, displaces silver from silver nitrate, that is, a reaction will take place.

(b) Iron being more reactive that copper, displaces copper from copper sulphate by the following reaction:
Fe + CuSo4→ FeSo4 + Cu
Brown coating of copper is deposited on the iron rod. Colour of the solution becomes green due to the formation of ferrous sulphate.

(c) Copper reacts with moist carbon dioxide in the air in rainy season and a green coating is formed. This is due to the formation of copper carbonate.

(i) Account for the following: (a) White silver chloride turns grey in sunlight. (b) Brown coloured cooper powder on heating in air turns blacks into coloured substance. (ii) What do you mean by: (a) Displacement reaction? (b) Reduction reaction? (c) Combination reaction? Write balanced chemical equation. [CBSE 2011]

(i)
(a) Silver chloride turns grey on exposure to sunlight because of the following reaction:
2AgCl □(→┴sunlight ) 2Ag + Cl2
(b) Oxidation of copper powder take place. The oxide formed has a black colour.
2Cu + O2 □(→┴(heat ) ) 2CuO

(ii)
(a) Those reaction in which a more active element displaces a less active element from its compound are called displacement reaction.
Example : Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)
(b) The reaction in which hydrogen is added or oxygen is removed or gain of electrons take place.
Example: Fe+3 + e– → Fe+2
(c) The reaction in which two or more element or compound combine together to form a single compound are called Combination reaction.
Example: (i) CaO(s) + H2O(l) → Ca(OH)2(aq) + Heat

(a) What is balanced chemical equation? Why should chemical equation be balanced? (b) Write the chemical equation of the reaction in which the following changes has taken place: (i) Change in colour. (ii) Change in temperature. (iii) Formation of precipitate. [CBSE 2017]

(a) A chemical equation in which the total mass of the reactant is equal to the total mass of the product is called a balance chemical equation. It may also be defining as a chemical equation in which the number of atom of each element is equal on the reactant side as well as on the product side. It is only after balancing the chemical equation that we can find out how much of each product will be formed from certain quantities of the reactant, in terms of law of conservation of mass.

(b) Chemical Equation corresponding to different changes are given below:
(i) Change in colour:
Fe + CuSo4→ FeSo4 + Cu
(ii) Change in temperature:
CaO(s) + H2O(l) → Ca(OH)2(aq) + Heat
(iii) Formation of precipitate:
BaCl2 + Na2SO4 → BaSO4 + 2NaCl

Rancidity

Foods kept in the open are oxidised by the oxygen in air. Their taste and smell change. When kept in air – tight containers, the food doesn’t come into contact with air is not spoilt.



10th Science Chapter 1 Board Questions Set – 7 (5 Marks)
(a) Illustrate an activity, to show that a change in the state of matter and change in temperature take place during a chemical reaction. (b) Write balanced chemical equation for the following reaction: (i) Natural gas burns and combines with oxygen to produce carbon dioxide and water. (ii) Ferrous sulphate crystals on heating break up into ferric oxide, Sulphur dioxide and Sulphur trioxide. [CBSE 2015]

(a) Take about 5kg of quicklime in a beaker and add to it about 50 ml of water. A brisk reaction takes place and a lot of heat is evolved.
CaO(s) + H2O(l) → Ca(OH)2(aq) + Heat
Quick lime is a white solid but after the reaction, calcium hydroxide is formed which is soluble in water and a clear solution is obtained. Thus, there has been a change in state of matter and change temperature.

(b)
(i) CH4 + 2O2 → CO2 + 2H2O
(ii) 2FeSo4. 7H2O□(→┴heat ) Fe2O3 + SO2 + SO3 + 14H2O

(a) Balance the chemical equation: (i) NaOH + H2So4 → Na2So4 + H2O. (ii) PbO + C→ Pb + CO2. (iii) Fe2O3 + Al → Al2O3 + Fe + Heat. (b) Write the balanced chemical equation for the following reaction: (i) Barrium chloride + Potassium sulphate → Barrium sulphate. (ii) Zinc + Silver nitrate → Zinc nitrate + silver. [CBSE 2016]

(a)
(i) 2NaOH + H2So4 → Na2So4 + 2H2O
(ii) 2PbO + C→ 2Pb + CO2
(iii) Fe2O3 + 2Al → Al2O3 + 2Fe + Heat

(b)
(i) BaCl2 + K2SO4 → BaSO4 + 2KCL
(ii) Zn + 2AgNO3 → Zn(NO3)2 + 2Ag

Rusting of Iron Articles

Iron articles on keeping in the open for a long time react with oxygen and moisture and forms the rust on the surface. Articles loss their shine because of this.



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