Chapter 6 Chemical Reaction and Catalyst

RBSE Solutions for Class 10 Science Chapter 6 Chemical Reaction and Catalyst.

In this article we will discuss short question, very short question and long question and answers of the Chapter 6 Chemical Reaction and Catalyst.

RBSE Solutions for Class 10 Science Chapter 6 Chemical Reaction and Catalyst.

Textbook Questions Solved

I. Multiple Choice Questions

Question 1:
Which change happens when FeCl3 changes to FeCl2 ?
(a) Oxidation
(b) Reduction
(c) Decomposition
(d) Combination
Answer:
(b) Reduction

Question 2:
When a substance breaks down into simple molecules, then which type of reaction happens?
(a) Decomposition
(b) Displacement
(c) Oxidation
(d) Combination
Answer:
(a) Decomposition

Question 3:
Substances which donate electrons are known as?
(a) Oxidizing agent
(b) Catalyst
(c) Reducing agent
(d) None of these
Answer:
(e) Reducing agent

Question 4:

Reactions which happen in both directions are known as?
(a) Oxidation
(b) Reduction
(c) Irreversible
(d) Reversible
Answer:
(d) Reversible

Question 5:
Substance which increases the speed of reaction is known as?
(a) Catalyst
(b) Oxidizing Agent
(c) Reducing agent
(d) None of these
Answer:
(a) Catalyst

Question 6:
Enzymes are which type of catalyst?
(a) Negative catalyst
(b) Positive catalyst
(c) Autocatalyst
(d) Bio-catalyst
Answer:
(d) Bio-catalyst

Question 7:
What is happening to magnesium in this reaction: 2Mg + O2 → 2MgO?
(a) Oxidation
(b) Reduction
(c) Decomposition
(d) Displacement
Answer:
(a) Oxidation

Question 8:
Which symbol is used for reversible reaction?
(a) →
(b) ↑
(c) ↓
(d) ⇌
Answer:
(d) ⇌

Question 9:
A reaction which is catalyst by its own product is known by which name?
(a) Biochemical
(b) Reversible
(c) Autocatalysis
(d) Irrevprsible
Answer:
(c) Autocatalysis

Question 10:
What happens in exothermic reaction?
(a) Heat is released
(b) Heat is absorbed
(c) Heat is distributed
(d) None of these
Answer:
(a) Heat is released

Chemical Reaction and Catalyst Very Short Answer Type Questions

Question 11:
What is a chemical change?
Answer:
A change after which a new substance is formed is called a chemical change.

Question 12:
Name the catalyst which facilitates change of vegetable oil to vegetable ghee.
Answer:
Nickel

Question 13:
Name different types of catalyst.
Answer:
Homogeneous catalyst, heterogeneous catalyst, positive catalyst, negative catalyst, autocatalyst, bio-catalyst

Question 14:
This is an example of which type of reaction: Zn + CuS04 → ZnS04 + Cu?
Answer:
Displacement reaction

Question 15:
Give an example of redox reaction.
Answer:
2Mg + O2 → 2MgO
Here Mg gets oxidised and oxygen gets reduced.

Question 16:
What is a reversible reaction?
Answer:
When a reaction takes place in both directions, it is called reversible reaction. In a reversible reaction, the moment a product is formed it starts changing into reactant.

Question 17:
What is the purpose of catalyst promoter and catalyst poison?
Answer:
Catalyst promoter enhances the action of a catalyst, while catalyst poison suppresses the action of a catalyst.

Question 18:
Which type of reaction happens between an acid and a base?
Answer:
Neutralisation

Question 19:
How many types of reactions are there on the basis of speed?
Answer:
Slow reaction and fast reaction

Question 20:
Give an example of thermal decomposition reaction.
Answer:
When calcium carbonate is heated up to 473K, we get calcium oxide and carbon dioxide.
CaCO3  CaO + CO2

Question 21:
What is the function of catalyst in a chemical reaction?
Answer:
Catalyst alters the speed of a chemical reaction.

Question 22:
What is the fundamental principle for balancing a chemical equation?
Answer:
Law of conservation of mass is the fundamental principle for balancing a chemical equation. Law of Conservation of Mass: Mass cannot be created and cannot be destroyed.

Question 23:
What is a redox reaction?
Answer:
Reaction in which oxidation and reduction takes place simultaneoulsy is called as redox reaction.

Question 24:
Burning of coal is which type of reaction?
Answer:
Oxidation

Question 25:
What will be the pH of a solution obtained after reaction between a strong acid and a strong base?
Answer:
pH = 7

Chemical Reaction and Catalyst Short Answer Type Questions

Question 26:
What is the difference between physical change and chemical change?
Answer:

Physical Change	Chemical Change
There are changes in physical characteristics of substance.	There are changes in chemical characteristics of substance.
No new substance is formed after this change.	New substance is formed after this change.
Change is reverted when cause of change is removed.	Change does not get reversed even when cause of change is removed.
This is a temporary change.	This is usually a permanent change.

Auto catalyst: When product of the reaction enhances the speed of the reaction
Example: CH3COOC2H5 + H2O → CH3COOH + C2H5OH
Bio-catalyst: Substance that catalyse biochemical reactions
Example: Maltose  Glucose

Question 27:
Explain combination and decomposition reactions with suitable examples.
Answer:
When two or more reactants combine to give one product, the reaction is called combination reaction. Example: when carbon is burnt in air, it gives carbon dioxide.
C + O2 → CO2
Decomposition Reaction: When a reactant dissociates to give two or more products, the reaction is called decomposition reaction.
Example : decomposition of water by electrolysis.
2H2 O (l)  2H2(g) + O2(g)

Question 28:
Following is an example of which type of reaction:
AgNO3 + KCl → AgCl + KNO3? Explain.
Answer:
This reaction shows double displacement. Here, silver displaces potassium to form silver chloride. On the other hand, potassium displaces silver to form potassium nitrate.

Question 29:
Explain oxidation and reduction on the basis of exchange of electrons.
Answer:
When an element loses electrons, it results in oxidation of that element. When an element gains electrons, its results in reduction of that element.
Oxidation:
Na → Na+ + e– ; 2Cl– → Cl2 + 2e–
Reduction: Cl + e– → Cl– ; Mg2+ + 2e– → Mg

Question 30:
Explain different types of catalyst.
Answer:
On the basis of physical state:
Homogeneous Catalyst: When the catalyst, reactants and products all are in the same physical state.

Heterogeneous Catalyst: When the catalyst, reactants and products are in different physical states.

On the basis of action:
Positive catalyst: When catalyst enhances the speed of reaction.
Example:

Negative catalyst: When catalyst reduces the speed of reaction.
Example:

Question 31:
Explain different types of decomposition reaction.
Answer:
Based on the cause of reaction, decomposition reactions are of following types:

• Electrical Decomposition: When electric current is passed through molten or aqueous form of a substance and the substance dissociates into two or more products.
• Thermal Decomposition: When decomposition reaction takes place due to heat, it is called thermal decomposition.
• Photo Decomposition: When decomposition reaction takes place due to light, it is called photo decomposition.

Question 32:
Chloroform is stored with a small amount of ethyl alcohol. Why?
Answer:
Chloroform has a tendency to react with oxygen from air. This reaction results in production of phosgene which is a poisonous gas. Ethanol is added to chloroform to prevent this reaction.

Question 33:
When a weak acid reacts with a strong base, the resulting salt solution is alkaline. Why?
Answer:
When a weak acid reacts with a strong base, there is incomplete ionization of the acid and there are OH–ions in the solution from strong base. Due to this, the resulting solution is alkaline.

Question 34:
Are following reactions possible? Justify your answer.
(i) Cu + ZnSO4 → CuSO4 + Zn
(ii) Fe + CuSO4 → FeSO4 + Cu
Answer:
(i) This reaction is not possible because copper is less reactive than zinc. Copper cannot displace zinc.
(ii) This reaction is possible because iron is more reactive than copper. Iron can displace copper.

Question 35:
Find oxidation and reduction in following reactions:
(i) C + O2 → CO2
(ii) Mg + Cl2 → MgCl2
(iii) ZnO + C → Zn + CO
(iv) Fe2O3 + 3CO → 2Fe + 3CO2
Answer:
(i) Oxidation of carbon and reduction of oxygen
(ii) Oxidation of magnesium and reduction of chlorine
(iii) Reduction of zinc oxide and oxidation of carbon
(iv) Reduction of iron oxide and oxidation of carbon monoxide

Chemical Reaction and Catalyst Long Answer Type Questions

Question 36:
Explain different types of chemical reactions.
Answer:
Following are different types of chemical reaction:
Combination reaction
When two or more reactants combine to give one product, the reaction is called combination reaction.
A+B → AB
Example: When carbon is burnt in air, it gives carbon dioxide.
C + O2 → CO2
When magnesium ribbon is burnt in air, it gives magnesium oxide.
2Mg + O2 → 2MgO

Displacement reaction
When an atom or group of atoms in one reactant displaces another atom or group of atoms from another reactant, the reaction is called displacement reaction. In this case, a more reactive atom or group of atoms displaces a less reactive atom or group of atoms.
AB + C → AC + B
Example: When zinc granules are kept in copper sulphate solution, the blue colour or copper sulphate fades away. This happens because zinc displaces copper to form zinc sulphate.

Double displacement reaction
When an atom or group of atoms in both reactants displaces each other, the reaction is called double displacement reaction.
AB +CD → AD+ CB
Example: When sodium hydroxide reacts with copper sulphate, then hydroxide and sulphate ions displace each other and copper hydroxide and sodium sulphate are formed.
CuSO4 + 2NaOH → Cu(OH)2 + Na2SO4

Decomposition reaction
When a reactant dissociates to give two or more products, the reaction is called decomposition reaction.
AB → A + B
Example: Calcium carbonate is heated to get calcium oxide and carbon dioxide.
CaCO3  CaO + CO2

Question 37:
What do you understand by oxidation-reduction? Explain with suitable examples.
Answer:
Oxidation and reduction can be defined on following bases.
Association or decomposition of oxygen: When oxygen is added to a substance, the substance is said to
be oxidized. When oxygen is removed from a substance, the substance is said to be reduced. In other words, addition of oxygen is called oxidation and removal of oxygen is called reduction.
Example: 2Mg + O2 → 2MgO
Association or decomposition of hydrogen: When hydrogen is added to a substance, the substance is said to be reduced. When hydrogen is removed from a substance, the substance is said to be oxidized. In other words, addition of hydrogen is called reduction and removal of hydrogen is called oxidation.
Example: 2H2S + O2 → 2H2O + 2S
Association or decomposition of electropositive elements: Removal of electropositive element from a substance is called oxidation. Addition of electropositive element to a substance is called reduction.
Example: 2Kl + Cl2 → 2KCl + l2
Association or decomposition of electronegative elements: Addition of electronegative element to a substance is called oxidation. Removal of electronegative element from a substance is called reduction.
Example: 2FeCl3 + H2 → 2FeCl2 + 2HCl
Exchange of electrons: When an element loses electrons, it results in oxidation of that element. When an element gains electrons, its results in reduction of that element. Example: Na → Na+ + e–, 2Cl– → Cl2 + 2e–

Question 38:
What do you know about types of catalyst and about characteristics of catalyst?
Answer:
Following are different types of catalyst:
Homogeneous Catalyst: When the catalyst, reactants and products, all are in the same physical state, the catalyst is called homogeneous catalyst. Following are some examples of homogeneous catalyst.

Heterogeneous Catalyst: When the catalyst, reactants and products are in different physical states, the catalyst is called heterogeneous catalyst. Following are some examples of heterogeneous catalyst.

Moreover, catalysts are categorized on other criteria as well. Other types are: slow catalyst, fast catalyst, auto-catalyst, bio-catalyst, etc.
On the basis of action
Positive catalyst: When catalyst enhances the speed of reaction.
Example:

Negative catalyst: When catalyst reduces the speed of reaction.

Characteristics of catalyst:

• Catalyst only alters the speed of a reaction but never participates in the reaction.
• A minute quantity of catalyst is enough.
• Each reaction has a specific catalyst and a catalyst cannot work for all reactions.
• Catalyst doesn’t initiate a reaction.
• Catalyst has same action on forward reaction and backward reaction.

Question 39:
Write the steps of writing chemical equation. What are the characteristics of a chemical equation?

Answer:
Following are different steps of writing a chemical equation:

• Reactants’ symbols are written, followed by an arrow. A sign of addition (+) is written between formulae of two reactants.
• Products’ symbols are written on RHS of arrow.
• State of matter of reactants and products is shown by s (for solid), l(for liquid) and g (for gas) in brackets, after the formula.
• Special conditions, if any, is written above or below the arrow.
• Number of atoms of each element should be same on both sides of the arrow.

Characteristics of Chemical Equation
Chemical equation gives brief information about chemical reaction. They are as follows:

• Complete information about reactants and products, e.g. number of molecules, mass, etc.
• Physical states of substances.
• Necessary conditions for chemical equation, e.g. temperature, pressure, catalyst, etc.
• Equation also shows if reaction is exothermic or endothermic.
• Equation also shows reversibility of chemical reaction.

Question 40:
Differentiate between following:

(a) Reversible and irreversible reactions
Answer:
A reversible reaction proceeds in both directions but an irreversible reaction happens only in forward direction.

(b) Catalyst promoter and catalyst poison
Answer:
A catalyst promoter enhances the efficacy of a catalyst, but a catalyst poison suppresses the function of a catalyst.

(c) Homogeneous and heterogeneous catalysts
Answer:
When physical state of catalyst, reactants and products is same, it is a homogeneous catalyst. When physical states of catalyst, reactants and products are different, it is a heterogeneous catalyst.

(d) Oxidation and reduction
Answer:
Addition of oxygen to a substance is called oxidation, while removal of oxygen from a substance is called reduction.

Chemical Reaction and Catalyst Additional Questions Solved

I. Multiple Choice Questions

Question 1:
In the reaction, SO2 (g) + 2H2S (g) → 2H2O(l) + S(s), the reducing agent is
(a) SO2
(b) H2O
(c) H2S
(d) S
Answer:
(c) H2S

Question 2:
Which information is not conveyed by a balanced chemical equation?
(a) Physical states of reactants and products
(b) Symbols and formula of all the substances involved in a particular reaction
(c) Number of atoms/molecules of the reactants and products formed
(d) Whether a particular reaction is actually feasible or not
Answer:
(d) Whether a particular reaction is actually feasible or not

Question 3:
Chemically rust is
(a) hydrated ferrous oxide
(b) only ferric oxide
(c) hydrated ferric oxide
(d) none of these
Answer:
(c) hydrated ferric oxide

Question 4:
Which of the following are exothermic processes?
(i) Evaporation of water
(ii) Dilution of an acid (H2SO4)
(iii) Reaction of water with quick lime
(iv) Sublimation of camphor (crystals)
(a) (i) and (ii)
(b) (iii) and (iv)
(c) (i) and (iv)
(d) (ii) and (in)
Answer:
(d) (ii) and (in)

Question 5:
The following reaction is an example of
4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g)
(i) displacement reaction
(ii) combustion reaction
(iii) redox reaction
(iv) neutralisation reaction
(a) (i) and (iv)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (ii)
Answer:
(b) (ii) and (iii)

Question 6:
Methane on combustion gives
(a) CO2
(b) H2O
(c) both CO2 and H2O
(d) neither CO2 nor H2O
Answer:
(c) both CO2 and H2O

Question 7:
The electrolytic decomposition of water gives H2 and 02 in the ratio of
(a) 1: 2 by volume
(b) 2:1 by volume
(c) 8 :1 by mass
(d) 1: 2 by mass
Answer:
(b) 2 :1 by volume

Question 8:
In the decomposition of lead (II) nitrate to give lead (II) oxide, nitrogen dioxide and oxygen gas, the coefficient of nitrogen dioxide (in the balanced equation) is
(a) 1
(b) 2
(c) 3
(d) 4
Answer:
(d) 4

Question 9:
Which of the following reaction is used in white washing of walls?
(a) 2Ca + O2 → 2CaO
(b) CaO + H2O → Ca(OH)2
(c) Ca(OH)2 + CO2 → CaCO3 + H2O
(d) Ca(OH)2CaO + H2O
Answer:
(c) Ca(OH)2 + CO2 → CaCO3 + H2O

Question 10:
Fatty foods become rancid due to the process of
(a) oxidation
(b) corrosion
(c) reduction
(d) hydrogenation
Answer:
(a) oxidation

Question 11:
We store silver chloride in a dark coloured bottle because it is
(a) a white solid
(b) undergoes redox reaction
(c) to avoid action by sunlight
(d) none of the above
Answer:
(c) to avoid action by sunlight

Question 12:
Silver article turns black when kept in the open for a few days due to formation of
(a) H2S
(b) AgS
(c) AgSO4
(d) Ag2S
Answer:
(d) Ag2S

Question 13:
Based on the reaction given below, what is the correct increasing order of reactivity of metals?

Answer:
(a) Ag < Cu < Fe

Question 14:
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) A colourless and odourless gas is

Question 15:
When carbon dioxide is passed through lime water,
(a) calcium hydroxide is formed
(b) white precipitate of CaO is formed
(c) lime water turns milky
(d) colour of lime water disappears.
Answer:
(c) lime water turns milky

Question 16:
In which of the following chemical equations, the abbreviation represent the correct states of the reactants and products involved at reaction temperature?
(a) 2H2(g) + O2(g) → 2H2O(l)
(b) 2H2(g) + O2(l) → 2H2O(l)
(c) 2H2(g) + O2(g) → 2H2O(g)
(d) 2H2(l) + O2(l) → 5.2H2O(g)
Answer:
(a) 2H2(g) + O2(g) → 2H2O(l)

Question 17:
Identify the following type of reaction:

(a) It is a combination reaction.
(b) It is a decomposition reaction and is accompanied by release of heat.
(c) It is a photochemical decomposition reaction and exothermic in nature.
(d) It is a decomposition reaction and is endothermic in nature.
Answer:
(d) It is a decomposition reaction and is endothermic in nature.

Question 18:
What is true about the following equation?

(i) Iron metal is being oxidised
(ii) Water is being reduced
(iii) Water is acting as reducing agent
(iv) Water is acting as oxidising agent
(a) (i), (ii) and (iii)
(b) (ii) and (iv)
(c) (i), (ii) and (iv)
(d) (ii) and (iv)
Answer:
(c) (i), (ii) and (iv)

Question 19:
When a magnesium ribbon is burnt in air, the ash formed is
(a) black
(b) white
(c) yellow
(d) pink
Answer:
(b) white

Question 20:
In which of the following, heat energy will be evolved?
(a) Electrolysis of water
(b) Dissolution of NH4Cl in water
(c) Burning of L.P.G.
(d) Decomposition of AgBr in the presence of sunlight
Answer:
(c) Burning of L.P.G.

Question 21:
Rancidity can be prevented by
(a) adding antioxidants
(b) storing food away from light
(c) keeping food in refrigerator
(d) all of these
Answer:
(d) all of these

Question 22:
Which of the following is not an example of single displacement reaction?
(a) CuO + H2→ H2O + Cu
(b) Zn + CuSO4→ ZnSO4 + Cu
(c) 4NH3 + 5O2 → 4NO + 6H2O
(d) Zn + 2HCL → H2 + ZnCL2
Answer:
(c) 4NH3 + 5O2 → 4NO + 6H2O

Question 23:
The reaction of H2 gas with oxygen gas to form water is an example of
(a) combination reaction
(b) redox reaction
(c) exotherntic reaction
(d) all of these reactions
Answer:
(a) combination reaction

Question 24:
In the reaction
CuO + H2 → Cu + H2O, the correct statement is
(a) CuO is an oxidising agent
(b) H2 is getting oxidised
(c) The reaction is a displacement reaction
(d) All of these
Answer:
(d) All of these

Question 25:
The reaction in which two compounds exchange their ions to form two new compounds is called
(a) displacement reaction
(b) combination reaction
(c) double displacement reaction
(d) redox reaction
Answer:
(c) double displacement reaction

Question 26:
On immersing an iron nail in CuS04 solution for few minutes, you will observe
(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:
(d) the colour of solution changes to green

Question 27:
An element X on exposure to moist air turns reddish-brown and a new compound Y is formed. The substance X and Y are
(a) X = Fe, Y = Fe2O3
(b) X = Ag, Y = Ag2S
(c) X = Cu, Y = CuO
(d) X = Al, Y = Al2O3
Answer:
(a) X = Fe, Y = Fe2O3

Chemical Reaction and Catalyst Very Short Answer Type Questions

Question 1:
Give the formula for lime.
Answer:
CaO

Question 2:
Give the formula for iron(II) oxide and iron (III) oxide.
Answer:
FeO is iron (II) oxide
Fe2O3 is iron (III) oxide

Question 3:
Give the formula for rust.
Answer:
Fe2O3.2H2O

Question 4:
Name the conditions necessary for rusting.
Answer:
Oxygen and moisture

Question 5:
Name the reaction seen during rancidity of food.
Answer:
Oxidation

Question 6:
Name the different forms of energy required for breaking down the reactants in decomposition reaction.
Answer:
Heat, light and electricity

Question 7:
What is the insoluble substance formed in a chemical reaction called?
Answer:
Precipitate

Question 8:
What does (II) in lead (II) nitrate indicate?
Answer:
It indicates that the valency of lead in this case is 2 and it forms +2 ions.

Question 9:
What are noble metals?
Answer:
Metals which do not react at any temperature, e.g., gold.

Question 10:
Name two metals which do not corrode?
Answer:
Gold and platinum

Question 11:
Name the products obtained when silver bromide is exposed to sunlight.
Answer:
Silver and bromine

Question 12:
Name the gas which bums with pop sound.
Answer:
Hydrogen gas

Question 13:
Name the compound used to test the evolution of carbon dioxide gas.
Answer:
Calcium hydroxide solution (freshly prepared), also called lime water, is used to test CO2 gas.

Question 14:
Name the gas evolved when lead nitrate is heated.
Answer:
Nitrogen dioxide gas.

Question 15:
Write the formula for two oxides of sulphur.
Answer:
SO2 and SO3

Question 16:
Give the examples of exothermic reaction.
Answer:
Respiration and water added to lime

Question 17:
Give one example of decomposition reaction that occurs in nature,
Answer:
Rotting of fruits and vegetables

Question 18:
Name the type of reaction in which two or more than two reactants form a single compound.
Answer:
Combination reaction

Question 19:
Name the chemical used in black and white photography.
Answer:
Silver bromide

Question 20:
Name the ions present in barium sulphate.
Answer:
Ba2+ and SO42-

Question 21:
Name the reaction which forms insoluble salts.
Answer:
Precipitation reaction

Question 22:
State the reaction in which hydrogen acts as a reducing agent.
Answer:
CuO + H2 Cu + HzO

Question 23:
Give one example of decomposition reaction in which solid and gas are two products obtained.
Answer:
CaCO3 → CaO + CO2
CaO is a solid and carbon dioxide is a gas.

Chemical Reaction and Catalyst Short Answer Type Questions

Question 1:
What happens when carbon dioxide and water react in the same ratio?
Answer:
When 6 molecules of carbon dioxide and 6 molecules of water react together glucose is formed with the evolution of oxygen gas.
6CO2 + 6H2O → C6H12O6 + 6O2

Question 2:
How can you chemically remove the black coating of copper oxide?
Answer:
The black coating of copper oxide can be removed chemically by passing hydrogen gas over heated copper oxide. The black coating turns brown as oxygen is removed by hydrogen.

Question 3:
Product formed when A and B react together are zinc chloride and hydrogen gas. Find reactant A and B.
Answer:
The reactant A is zinc metal and the reactant B is hydrochloric acid.
Zn + 2HCl → ZnCl2 + H2

Question 4:
Name the product obtained and type of reaction given below:
Na2 SO4 + BaCl2 _____ + _____
Answer:
The products obtained in the above reaction are as follows:
Na2SO4 + BaCl2 → BaSO4 + 2NaCl
The reaction is double displacement.

Question 5:
When quick lime is added to water a hissing sound is produced. Write the chemical reaction and name the type of reaction taking place.
Answer:
CaO + H2O → Ca(OH)2 + ∆
It is exothermic and combination reaction.

Question 6:
Three test tubes are taken and labelled as A, B and C. In test tube A iron nail is dipped in water. Invest tube B iron nail is dipped in mixture of water and oil and in test tube C iron nail is added with dry calcium chloride. Name the test tube in which the iron nail will rust and why?
Answer:
The iron nail will rust in test tube A because it provides the condition reuired for rusting, both moisture as well as air is present in it.

Question 7:
Metal X becomes green when left in air, turns black when heated in air. Name the metal and the compounds formed in both the cases.
Answer:
X is copper.
Green compound is due to formation of copper carbonate and black colour compound is due to the formation of copper oxide.

Question 8:
Give two examples of a reaction which is both endothermic and decomposition in nature.
Answer:

Question 9:
Explain why most of the metal articles become dull when kept exposed to air?
Answer:
Metal articles react with the gases present in the air and their surface gets coated with the layer of compound it forms making them look dull and the lustre is lost. For example, aluminium metal reacts readily with oxygen to form aluminium oxide and its surface becomes dull.

Question 10:
What is rancidity? What is the general name of chemicals which are added to fat and oil containing food so as to prevent the rancidity?
Answer:
The oil and fat containing food when left exposed to air reacts with oxygen oxidized and become rancid, this process is called rancidity. In this process their smell and taste changes. The general name of the chemicals that are added to prevent this oxidation are called as antioxidants. For example, nitrogen gas is an antioxidant.

Question 11:
Define displacement reaction. Give one example of it, how is it different from double displacement reaction?
Answer:
The reaction in which more reactive metal displaces (takes place of) the less reactive metal from its compound, is called as displacement reaction.
e.g., Fe + CuSO4 → FeSO4 + Cu
It is different from double displacement reaction because in double displacement reaction two different elements or atoms or ions are exchanged for each other,
e.g., Na2 SO4 + BaCl2 → BaSO4 + 2NaCl

Question 12:
Give differences between the exothermic and endothermic reactions.
Answer:
Exothermic reaction: In this reaction heat is given out during the reaction. Endothermic reaction: In this reaction heat is taken in to break the bonds and to form new compounds.

Question 13:
Explain and name the type of reaction seen when iron reacts with hydrochloric acid.
Answer:
Iron reacts with HCl  to release hydrogen gas and chloride salt of iron is formed. This reaction is called as displacement reaction,

Question 14:
Why is photosynthesis considered as endothermic reaction?
Answer:
Photosynthesis is a reaction in which energy is required to form glucose from carbon dioxide and water. Energy in the form of sunlight is required to break the bonds of hydrogen and oxygen. Hence it is termed as endothermic reaction.

Question 15:
What is electrolytic decomposition? Give two uses of electrolytic decomposition reaction.
Answer:
When electricity is passed through a molten compound which is ionic in nature, then the ions of the compound separate into its components thereby decomposing the compound.
It is used in separating hydrogen and oxygen gas from water. It is also used to separate gases or metals (elements) from the compound.

Question 16:
Give one example for each of the following reactions:
(a) Combination reaction
(b) Decomposition reaction
(c) Displacement reaction
Answer:
(a) Combination reaction
2Mg + O2 → 2MgO
(b) Decomposition reaction
CaCO3  CaO + CO2
(c) Displacement reaction
Zn + CuSO4 → ZnSO4 + Cu

Question 17:
Give three ways used to prevent rusting.
Answer:
(i) Oiling of metals
(ii) Applying paints
(iii) Making an alloy

Question 18:
Define corrosion, rusting and rancidity.
Answer:
Corrosion: Metals when kept exposed, it reacts with air moisture, acids and other gases present in atmosphere and get corrode. This process is called corrosion. Rusting: Iron metal when left exposed, it reacts with moisture and air and get coated with reddish brown powdery substance called rust, this process is called rusting. Rancidity: Food containing fats and oil when exposed to air gets oxidised and gives bad taste and smell to food. This process is called rancidity.

Question 19:
Name the type of reaction for the following:
(i) Vegetable matter changing into compost.
(ii) Burning of natural gas.
(iii) Adding water to quick lime to form slaked lime.
Answer:
(i) Vegetable matter changing into compost is exothermic and decomposition reaction.
(ii) Burning of natural gas is exothermic reaction.
(iii) Adding water to quick lime to form slaked lime is combination reaction and exothermic in nature.

Question 20:
How can one make an equation more informative?
Answer:
To make a chemical equation more informative:
(i) The physical state of the reactants and products are mentioned like gaseous (g), liquids (1), aqueous (a), solid (s).
(ii) Conditions such as temperature, pressure, catalyst is mentioned above/ below the arrow in the equation.

Question 21:
Give the chemical equations (balanced) for the following:
(1) Reaction used in black and white photography.
(2) Reaction when glucose is oxidised.
(3) Formation of water from H2 and O2 .
Answer:

Question 22:
Give equations to show the chemical reactions of zinc and lead where it displaces copper from its compound.
Answer:

Question 23:
Explain oxidation and reduction reaction with examples.
Answer:
Oxidation reaction: The reaction in which oxygen is gained or hydrogen is lost, is called oxidation reaction.

Reduction reaction: The reaction in which hydrogen is gained or oxygen is lost, is called reduction reaction.

Question 24:
What happens chemically when quick lime is added to water?
Answer:
Quick lime is CaO. On adding water to it large amount of heat is released, with the formation of Ca (OH)2.
CaO + H2O → Ca(OH)2

Question 25:
How will you test for the gas which is liberated when hydrochloric acid reacts with an active metal?
Answer:
The gas liberated is hydrogen and it can be tested by taking a burning match stick near the mouth of the test tube in which reaction is taking place. The match stick will extinguish with a pop sound.

Question 26:
What is an oxidation reaction? Identify in the following reactions:
(i) the substance oxidized and
(ii) the substance reduced.
ZnO + C → Zn + CO
Answer:
The reaction in which a substance looses hydrogen or gains oxygen, is called oxidation reaction. In the given reaction C is oxidized as it gains oxygen and ZnO is reduced as it looses oxygen.

Question 27:
Give an example of photochemical reaction.
Answer:
In black and white photography, AgBr gets decomposed due to light and forms Ag and bromine gas.

Question 28:
Give an example of a decomposition reaction. Describe an activity to illustrate such a reaction by heating.
Answer:
Example of decomposition reaction:

Activity:
Take a test tube add CaC03 in it and heat. Gas is evolved, allow it to pass through lime water which turns milky.

Question 29:
Balance the following chemical equation:
Fe(s) + H2O(g) → Fe3O4(s) + H2(g)
Answer:
3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)

Question 30:
Why is respiration considered as exothermic process?
Answer:
During respiration heat is released so it is termed as an exothermic reaction.
C6H12O6 + 6O2 → 6CO2 + 6H2O + energy

Question 31:
Balance the following chemical equation:
FeSO4  Fe2O3 + SO2 + SO3
Answer:
2FeSO4  Fe2O3 + SO2 + SO3

Question 32:
Balance the following chemical equation:
MnO2 + HC1 → MnCl2 + Cl2 + H2O
Answer:
MnO2 + 4HC1 → MnCl2 + Cl2 + 2H2O

Question 33:
On what basis is a chemical equation balanced?
Answer:
The number of atoms on left hand side of the reaction (i.e., reactants) is equal to the number of atoms on the right hand side of the equation (i.e., product).
Law of Conservation of Mass: Mass of atoms in chemical reaction can neither be created nor be destroyed, it remains the same.

Question 34:
State any two observations in an activity, which may suggest that a chemical reaction has taken place. Given examples to support your answer.
Answer:
The following observations in an activity may suggest that a chemical reaction has taken place:

• Change in state
• Change in colour
• Evolution of a gas
• Change in temperature

Question 35:
Identify the type of reaction in the following example:

Answer:
It is a double displacement reaction.

Question 36:
Identify the type of reaction in the following example:

Answer:
It is a displacement reaction. Fe displaces Cu from CuSO4.

Question 37:
Identify the type of reaction in the following example:
2H2(g) + O2(g) → 2H2O(g)
Answer:
It is a combination reaction.

Question 38:
Balance the given chemical equation:
HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O
Answer:
2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O

Question 39:
Balance the given chemical equation:
Al(s) + CuCl2(aq) → AlCl3(aq) + Cu(s).
Answer:
2Al(s) + 3CuCl2(aq) → 2AlCl3(aq) + 3Cu(s).

Question 40:
Balance the following chemical equation:

Answer:

Question 41:
Name a reducing agent that may be used to obtain manganese from manganese dioxide.
Answer:
Coke or carbon is used as a reducing agent.

Question 42:
In electrolysis of water, why is volume of gas collected over one electrode double that of gas collected over the other electrode?
Answer:
The volume of gas collected over one electrode is double than that of the gas collected over the other electrode as the ratio of H : O in water is 2 :1.

Question 43:
What change in colour is observed when silver chloride is left exposed to sunlight? What type of chemical reaction is this?
Answer:
Silver turns black, the reaction is decomposition.

Chemical Reaction and Catalyst Long Answer Type Questions

Question 1:
Name different types of chemical reactions. Give one example for each.
Answer:
Different types of chemical reactions are:
(a) Combination reactions: The reaction in which two or more than two substances combine together to form a single compound.
e.g., 2Mg + O2 → 2MgO
(b) Decomposition reaction: The reaction in which a compound decomposes to form two or more substances is called decomposition reaction.
e.g., CaCO3  CaO + CO2
(ic) Displacement reaction: The reaction in which more reactive metal displaces the less reactive metal is called displacement reaction.
e.g., Fe + CuSO4 → FeSO4 + CO2
(d) Double displacement reaction: The reaction in which two different atoms or groups of (substances) atoms exchange for each other is called double displacement reaction.
e.g., NaO2SOO4(aq) + BaClO2(aq) → BaSOO4(s) + 2NaCl(aq)
(e) Oxidation-reduction reaction: The reaction in which oxygen is added/ hydrogen is removed is called oxidation reaction.
The reaction in which hydrogen is added/oxygen is removed is called reduction reaction. e.g., Oxidation,

Question 2:
Give an activity to prove that water contains H : O in the ratio of 2 :1.
Answer:

1. Take a plastic mug. Drill two holes at its base and fit rubber stoppers in these holes. Insert carbon electrodes in these rubber stoppers as shown in figure.
2. Connect these electrodes to a 6 volt battery.
3. Fill the mug with water such that the electrodes are immersed. Add a few drops of dilute sulphuric acid to the water.
4. Take two test tubes filled with water and invert them over the two carbon electrodes.
5. Switch on the current and leave the apparatus undisturbed for some time.
6.  You will observe the formation of bubbles at both the electrodes. These bubbles displace water in the test tubes.
7. The gas collected in test tube attached to cathode is twice in volume than the gas collected at anode.
8. Once the test tubes are filled with the respective gases, remove them carefully.
9.  The burning match stick or candle when brought near to the test tube containing gas obtained at cathode, burns with a pop sound indicating the presence of hydrogen gas.
   

Question 3:
(i) What is rancidity?
(ii) Suggest two methods to reduce the problem of rancidity.
(iii) How is corrosion different from rusting?’
Answer:
(i) Rancidity: Fat and oil containing food when kept open in air gets oxidised and become rancid due to which the taste and smell of food changes.
(ii) Two methods to reduce rancidity are keep the food in closed containers and use antioxidants.
(iii) Corrosion is seen in metals, when kept exposed to form a layer of compound by reaction of metal with moisture, acid or gases present in it.
Rusting is the process in which iron metal reacts with air and moisture to form brownish flaky substance called rust.

Question 4:
What is meant by exothermic and endothermic reaction? Give examples to explain the same.
Answer:
Exothermic reactions: Those reactions in which heat is released out during chemical reactions.
e.g., burning of fuel

The natural gas (methane) bums in air to form carbon dioxide and water and releases large amount of heat.
Endothermic reaction: Those reactions in which heat is required, is called endothermic reaction.

Question 5:
Solid calcium oxide was taken in a container and water was added slowly to it.

(i) State the two observations made in the experiment.
(ii) Write the name and chemical formula of the product formed.
Answer:
(i) Calcium oxide reacts vigorously with water to produce slaked lime and large amount of heat is released.

Question 6:
What is an oxidation reaction? Give an example of oxidation reaction. Is oxidation an exothermic or an endothermic reaction?
Answer:
The reaction in which oxygen is added or hydrogen is removed is called oxidation reaction.
e.g., 2Cu + O2  2CuO
It is an endothermic reaction.

Question 7:
Define a combination reaction. Give one example of a combination reaction which is also exothermic.
Answer:
Combination reaction: It is a reaction in which two elements combine together to form a product.

Question 8:
(i) What is observed when a solution of potassium iodide is added to a solution of lead nitrate taken in a test tube?
(ii) What type of reaction is this?
(iii) Write a balanced chemical equation to represent the above reaction.
Answer:
(i) Yellow coloured precipitate is formed due to formation of lead iodide.
(ii) It is a double displacement reaction.
(iii) 2KI + Pb(NO3)2 → 2KNO3 + Pbl2

Question 9:
What is a redox reaction? When a magnesium ribbon burns in air with a dazzling flame and forms a white ash, is magnesium oxidised or reduced? Why?
Answer:
The reaction which shows both oxidation and reduction reaction in it is called redox reaction.
2Mg + O2 → 2MgO
In this case, magnesium is oxidised as oxygen combines with it.

Question 10:
Distinguish between an exothermic and an endothermic reaction. Amongst the following reactions, identify the exothermic and the endothermic reaction.
(i) Heating coal in air to form carbon dioxide.
(ii) Heating lime-stone in a lime kiln to form quick lime.
Answer:

Exothermic Reaction	Endothermic Reaction
The reaction in which heat is released.	The reaction in which heat is absorbed.

(i) Exothermic
(ii) Endothermic

Question 11:
Distinguish between a displacement reaction and a double displacement reaction. Identify the displacement and the double displacement reaction from the following reactions.

Answer:

Displacement Reaction	Double Displacement Reaction
The reaction in which more reactive metal displaces less reactive metals	The reaction in which  two different  atoms or group of atoms  exchange for each other.

(i) It is a double displacement reaction.
(ii) It is a displacement reaction.

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