Physical And Chemical Changes Test

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Physical And Chemical Changes Test - 4

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Weekly Quiz Competition

Question 1
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An example of a chemical change is:

A
Formation of clouds

B
Glowing of an electric light

C
Dropping sodium into water

D
Dissolving salt in water

Solution

Dropping sodium into water is a chemical change as sodium reacts with water to form sodium hydroxide and hydrogen gas along with the release of energy.

Question 2

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Study the Venn diagram given below and the table that follows.

	X	P	R
I	Digestion of food	Formation of alloy	Rusting of iron
II	Burning of fuels	Formation of soil	Burning of garbage
III	Rotting of garbage	Erosion of soil	Burning of wood
IV	Cooking of food	Stitching of clothes	Rancidity of food

Select the correct option regarding X, P and R.

I, II and IV

I, II and III

I, III and IV

II, III and IV

Solution

X: Digestion of food, burning of fuels and cooking of food are desirable chemical changes that are permanent in nature as the processes cannot be reversed.
P: Formation of alloy, formation of soil and stitching of cloth are permanent changes.
R: Rusting of iron is a permanent, chemical change and rust is a layer of iron oxide formed on the surface of the metal. It is not a desirable change since metal is wasted in the process. Similarly, burning of garbage and rancidity of food are permanent changes which are not desirable.
Hence, only option (1) is correct.

Question 3
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Analyse the two statements given below and select the correct option.

Statement I: Both physical and chemical changes may be accompanied by a change in state.
Statement II: Boiling of water is a chemical change because a gaseous product is formed.

A
Both statements I and II are correct and statement II is the correct reason for I.

B
Both statements I and II are correct, but statement II is not the correct reason for I.

C
Statement I is correct, but statement II is incorrect.

D
Both statements I and II are incorrect.

Solution

Statement I is correct, but statement II is incorrect because boiling of water is a physical change as no new substance is formed. Only the physical state of the substance changes during boiling.
Question 4
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While balancing an equation, which of the following is changed?

A
Molecular formula of the compound

B
Type of reactants

C
Stoichiometric coefficient

D
Type of products

Solution

Only the stoichiometric coefficients are changed while balancing a chemical equation.
There is no change in the reactants and the products or their formulae.
Question 5
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Analyse the given statements and choose the correct option:

A. Formation of a precipitate on mixing two solutions is a sure indication of a chemical change.
B. Both physical and chemical changes are associated with energy exchanges.
C. Occurrence of effervescence during a reaction indicates that the reaction mixture is boiling.
D. A colour change indicates that the reaction cannot be reversed by any physical or chemical means.

A
x - A, x - B, - C, - D

B
- A, x - B, x - C, - D

C
x - A, - B, x - C, x - D

D
- A, - B, x - C, x - D

Solution

The statements A and B are correct.
Occurrence of effervescence indicates the formation of a gaseous product. Hence, statement C is incorrect.
A colour change usually indicates the occurrence of a chemical change, which cannot be reversed by simple physical processes.
However, there are exceptions such as, an iron rod may be heated till red hot, which is a physical change and is reversible.
Hence, D is incorrect.
Question 6
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Identify the type of the given reaction:

2H₂O 2H₂ + O₂

A
Combination

B
Decomposition

C
Single replacement

D
Double replacement

Solution

2H₂O 2H₂ + O₂
The given reaction is a decomposition reaction as one reactant dissociates into more than one product.
Question 7
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Identify the type of the given reaction:

C₂H₆ + 5O₂ 3H₂O + 2CO₂

A
Combination

B
Decomposition

C
Double replacement

D
Combustion

Solution

Combustion is a process in which a substance reacts with excess of oxygen and the reaction proceeds with the release of energy in the form of heat and light.
During the combustion of hydrocarbons (compounds of carbon and hydrogen), the products invariably are carbon dioxide and water, along with the release of energy.
The given reaction is a combustion reaction.
Question 8
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What will be the respective coefficients in the given chemical equation?

?Mg + ?HCl 1MgCl₂ + ?H₂

A
1, 2, 1

B
2, 1, 1

C
2, 2, 2

D
1, 1, 2

Solution

The balanced chemical equation is as follows:

Mg + 2HCl MgCl₂ + H₂

Hence, option (1) is correct.
Question 9
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Refer to the flow chart given below and identify the incorrect statements regarding W, X, Y and Z.

I. W is a combination reaction.
II. W is always an endothermic process.
III. X could be a neutralisation reaction.
IV. Y could be the reaction of an acid with some metal bicarbonate.
V. Y could be a displacement reaction.

A
I and IV

B
II and III

C
II and IV

D
III and IV

Solution

I and IV are incorrect statements.

I. Since there is only one reactant, W cannot be a combination reaction.
Hence, statement I is incorrect.
II. W is probably a decomposition reaction and these reactions are always endothermic.
Hence, statement II is correct.
III. X has more than one reactant and no gaseous product is formed. This could be a neutralisation reaction.
Hence, statement III is correct.
IV. Since CO₂ gas is not given out, Y cannot be the reaction of an acid with some metal bicarbonate.
Hence, statement IV is incorrect.
V. Y could be a displacement reaction in which a reactive metal displaces hydrogen from solutions of acids.
Hence, statement V is correct.
Question 10
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Which of the following reactions is a double displacement reaction?

A
Mg + CuSO₄ MgSO₄ + Cu

B
BaCl₂ + CuSO₄ BaSO₄ + CuCl₂

C
2KBr + Cl₂ 2KCl + Br₂

D
NH₄O₂ N₂ + 2H₂O

Solution

A reaction that proceeds with the exchange of ions between the reactant species is called a double displacement reaction.

BaCl₂ + CuSO₄ BaSO₄ + CuCl₂
This is an example of a double displacement reaction.
Question 11
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A man painted his main gate that was made of iron. This is done in order to

(i) prevent it from rusting
(ii) protect it from the sunlight
(iii) make it look beautiful
(iv) make it dust free

Which of the above reasons is/are correct?

A
(i) and (ii) only

B
(ii) and (iii)

C
(ii) only

D
(i) and (iii)

Solution

Iron objects are painted in order to prevent rusting. This also improves the looks of the object.
Hence, (i) and (iii) are correct.
Question 12
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Corrosion is a chemical reaction that involves

A
bulk material of the object changing from an element to a compound

B
surface of the object changing from an element to a compound

C
wearing off of the surface due to friction with air

D
surface of the object changes from one element into another element

Solution

Corrosion is tarnishing of the metal surface due to reaction with atmospheric gases.
The reaction occurs at the surface of the metal which gets deposited with the compounds formed.
Question 13
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During an activity, following three test tubes are set up:

Test tube 1: A shiny iron nail is placed in a test tube along with anhydrous calcium chloride. Mouth of the test tube is covered with cotton wool.
Test tube 2: A test tube is filled with boiled water and a shiny nail is dropped in it. A layer of oil is placed on the surface of water.
Test Tube 3: A test tube is filled with tap water and a shiny iron nail is dropped in it. The test tube is left open.

In which of the test tubes will rusting not take place when observed after a week?

A
1 and 2

B
2 and 3

C
1 and 3

D
1, 2 and 3

Solution

Presence of both air and moisture is essential for rusting to take place.
In test tube 1, moisture is not available as it has been absorbed by anhydrous calcium chloride.
In test tube 2, air is not available as it got expelled on boiling the water and the layer of oil prevents more air from dissolving in the moisture.
Hence, rusting will not be observed in test tubes 1 and 2.
Question 14
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Identify the incorrect statement(s).

Statement I: All physical changes are spontaneous, but chemical changes have to be induced.
Statement II: All changes, physical as well as chemical, involve energy exchanges.

A
Only I

B
Only II

C
Both I and II

D
None

Solution

Statement I is incorrect as spontaneity of a process depends on the conditions available. Many physical as well as chemical processes are spontaneous under standard conditions. For example, evaporation of water is spontaneous and so is the reaction of Na metal with the water vapour in the air. Statement II is correct as both physical and chemical processes involve energy changes.

Question 15

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Match the following:

A. BaCl₂ + Na₂SO₄ BaSO₄ + 2NaCl	(i) Combination reaction
B. Mg + H₂O MgO + H₂	(ii) Double displacement reaction
C. 2KClO₃ 2KCl + 3O₂	(iii) Decomposition reaction
D. C + O₂ CO₂	(iv) Displacement reaction

A - (ii), B - (i), C - (iv), D - (ii)

A - (iv), B - (i), C - (ii), D - (i)

A - (ii), B - (iv), C - (iii), D - (i)

A - (iii), B - (iv), C - (ii), D - (i)

Solution

(A) BaCl₂ + Na₂SO₄ BaSO₄ + 2NaCl	(ii) Double displacement reaction
(B) Mg + H₂O MgO + H₂	(iv) Displacement reaction
(C) 2KClO₃ 2KCl + 3O₂	(iii) Decomposition reaction
(D) C + O₂ CO₂	(i) Combination reaction

Question 16
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Zinc oxide (ZnO) reacts with carbon (C) to produce zinc (Zn) and carbon monoxide (CO). The balanced chemical equation for the given reaction is ZnO (s) + C (s) Zn (s) + CO (g). Which of the following substances is reduced in the given reaction?

A
ZnO

B
C

C
CO

D
Zn

Solution

The given reaction is an example of a redox reaction. In a redox reaction, the substance that either gains oxygen or loses hydrogen is oxidised and the substance that loses oxygen or gains hydrogen is reduced. In the given reaction, zinc oxide (ZnO) loses oxygen to form zinc (Zn). Hence, ZnO is reduced in the given reaction.
Question 17
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Which of the following statements is true about the reaction of copper turnings with the silver nitrate solution?

A
The colour of the copper turnings kept in the silver nitrate solution is same as the colour of those kept aside.

B
An effervescence is observed.

C
The colour of the solution changes to blue.

D
There is no change in the colour of the solution.

Solution

The colour of the solution changes to blue as copper displaces silver from the solution to form copper nitrate.
Question 18
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Which of the following statements is not true about a substance that goes rancid?

A
Its smell changes.

B
Its taste changes.

C
Its colour changes.

D
It reduces in mass.

Solution

Rancidity is a term generally used to denote unpleasant odours, colour change and flavours in foods resulting from deterioration in the fat or oil portion of a food. There is no change in the mass observed, which is in agreement with the law of conservation of mass.
Question 19
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Which of the following phenomena is not an indication of a chemical change?

A
Evolution of a gas

B
Change in shape

C
Change in temperature

D
Change in colour

Solution

Change in the shape of a substance does not indicate that a chemical change has taken place.
Question 20
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The substances which prevent oxidation of food are called

A
oxidants

B
reductants

C
antioxidants

D
decomposers

Solution

Antioxidants are the substances used to slow down the process of oxidation.
They may be used to preserve food in order to prevent it from going rancid.