Model question paper for Basic Concepts of Chemistry and Chemical Calculations

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Questions:

Multiple Choice Question

14 x 1 = 14

Which form of based on physical characteristics possess neither definite volume nor definite shape?

(a)

Solids

(b)

Liquids

(c)

Gases

(d)

Both (a) and (b)

Which among the following statement(s) describe an element?
i) It is a pure substance which could be split into two or more simpler substance.
ii) It is a pure substance which cannot be split into simpler substance
iii) It's composition is not uniform
iv) All the above

(a)

only (iv)

(b)

only (ii)

(c)

(ii) and (iii)

(d)

(i) and (iii)

The characteristic feature of orderly arrangement of molecules belongs to ______________.

(a)

Solids

(b)

Liquid

(c)

Gases

(d)

None of these

The solid state of matter is converted into gas by

(a)

sublimation

(b)

deposition

(c)

freezing

(d)

condensation

Match the list I with List II and select the correct answer using. the code given below the lists.

List I		List II
A	Diamond	1	Heterogeneous mixture
B	Aerated drinks	2	Element
C	Distilled water	3	Homogeneous mixture
D	Sand	4	Compound

(a)

A	B	C	D
2	3	4	1

(b)

A	B	C	D
4	3	1	2

(c)

A	B	C	D
3	1	4	2

(d)

A	B	C	D
2	1	4	3

Consider the following statements
i) Matter possesses mass.
ii) 22-carat gold is a mixture.
iii) Dry ice is a compound.
Which of the following statement(s) given above is/ are correct?

(a)

1 & 3

(b)

Only 1

(c)

1 & 2

(d)

1,2, & 3

Identify the redox reaction taking place in a beaker.

(a)

Zn_(s)+ Cu²⁺_(aq) \(\longrightarrow\) Zn²⁺_(aq) + Cu_(s)

(b)

Cu_(s) + 2Ag⁺_(aq) \(\longrightarrow\) Cu²⁺_(aq) + 2Ag_(s)

(c)

Cu_(s) + Zn²⁺_(aq) \(\longrightarrow\) Zn_(s) + Cu²⁺ _(aq)

(d)

2Ag_(s) + cu²⁺_(aq) \(\longrightarrow\) 2Ag⁺_aq + Cu_(s)

In which of the following reactions, hydrogen peroxide acts as an oxidising agent?

(a)

I₂+ H₂O₂ + 20H^- \(\longrightarrow\) 21- + 2H₂O + O₂

(b)

PbS + 4H₂O₂ \(\longrightarrow\) PbSO₄ + 4H₂O

(c)

2MnO₄^-+ 3H₂O₂ \(\longrightarrow\) 2MnO₂ + 3O₂ + 2H₂O + 2OH^-

(d)

HOCI + H₂O₂ \(\longrightarrow\) H₂O⁺ + Cl^- + O₂

The change in the oxidation number of S in H₂S and SO₂,in the following industrial reaction:
2H₂S_(g) + SO_2(g) \(\longrightarrow\) 3S_(s) + H2O_(g)

(a)

-2 to 0, +4 to 0

(b)

-2 to 0, +4 to -1

(c)

-2 to -1, +4 to 0

(d)

-2 to -1, +4 to -2

10.

Maximum oxidation state is present in the central metal atom of which compound

(a)

CrO₂Cl₂

(b)

MnO₂

(c)

[Fe(CN)₆]^3-

(d)

MnO

11.

Match the items in column list-I with relevant items in list-II.

List-I		List-II
A	Ions having positive charge	1	anion
B	Ions having negative charge	2	-1
C	Oxidation number of fluorine in NaF	3	0
D	The sum of oxidation number of all atoms in a neutral molecule	4	cation

(a)

A	B	C	D
3	4	2	1

(b)

A	B	C	D
1	2	3	4

(c)

A	B	C	D
2	3	4	1

(d)

A	B	C	D
4	1	2	3

12.

Match the list-I with list-II and select the correct answer using the code given below the lists.

List-I		List-II
A	Cr₂O₇^2-	1	+5
B	MnO₄^-	2	+6
C	VO₃^-	3	+3
D	FeF₆³⁺	4	+7

(a)

A	B	C	D
3	1	4	2

(b)

A	B	C	D
4	3	2	1

(c)

A	B	C	D
2	4	1	3

(d)

A	B	C	D
3	2	1	4

13.

Identify the correct statement(s) with respect to the following reaction :
Zn + 2HCl \(\longrightarrow\) ZnCl₂ + H₂
(i) Zinc is acting as an oxidant
(ii) Chlorine is acting as a reductant
(iii) Hydrogen is not acting as an oxidant
(iv) Zn is acting as a reductant

(a)

only (ii)

(b)

only (iv)

(c)

both (ii) and (iii)

(d)

both (ii) and (i)

14.

Rusting of iron articles is an example of ___________ reaction

(a)

Combustion

(b)

decomposition

(c)

redox

(d)

hydrolysis

Assertion and reason

1 x 2 = 2

15.

Assertion (A): Among halogens fluorine is the best oxidant.
Reason (R): Fluorine is the most electronegative atom.
Codes:
(a) both assertion and reason are true and the reason is the correct explanation of assertion
(b) both assertion and reason are true but reason is not the correct explanation of assertion
(c) assertion is true but reason is false
(d) both assertion and reason are false

(a)

Both A and R are true and R explains A

(b)

Both A and R are true but R does not explain A

(c)

A is true but R is false

(d)

Both A and R are false

Generic 2

10 x 2 = 20

16.

Calculate the equivalent masses of the following - Ferrous Sulphate

17.

Calculate the equivalent masses of the following - Crystalline Oxalic acid, H₂C₂O₄ , 2H₂O

18.

Calculate the equivalent masses of the following - Oxalic acid H₂C₂O₄

19.

Calculate the equivalent masses of the following - HNO₃

20.

Calculate the equivalent masses of the following - HCl

21.

Give the relationship between the number of mole of the substance and its gram molecular mass.

22.

Give examples for the following redox reaction "Disproportionation."

23.

Why atomic masses are called as relative atomic masses?

24.

Give a brief account of classification of matter.

25.

Calculate the molar mass of the following compounds.
Sulphuric Acid [H₂SO₄]

Generic 3

18 x 3 = 54

26.

How much mass (in gram units) is represented by the following ?
0.2 mol of NH₃

27.

Calculate the mass of the following : 1 molecule of water.

28.

Calculate the mass of the following : 1 atom of silver

29.

Calculate the number of atoms in the following 52 moles of He.

30.

Explain the classification of matter based on chemical composition.

31.

How will you classify matter based on physical state ?

32.

Write a note on the differences between elements and compounds

33.

Matter is defined as anything that has mass and occupies space. All matter is composed of atoms

34.

By applying the knowledge of chemical classification, classify each of the following into elements, compounds or mixtures
Sugar

35.

Why is air sometimes considered as a heterogeneous mixture?

36.

Why is distilled water a compound whereas tap water is a mixture?

37.

'X' is an impure substance. Is it an element, compound or mixture?

38.

Which one of the two, ClO₂^- or ClO₄^- shows disproportionation reaction and why?

39.

Zn rod is immersed in CuSO₄ solution. What will your observe after an hour? Explain your observation in terms of the redox reaction.

40.

What is the most essential conditions that must be satisfied in a redox reaction?

41.

How would you know whether a redox reaction is taking place in an acidic, alkaline or neutral medium?

42.

2Cu₂S + 3O₂ \(\longrightarrow\) 2Cu₂O + 2SO₂
(i) In this reaction which substance is getting oxidised and which substance is getting reduced?
(ii) Name the oxidising and reducing agents.

43.

MnO₄^2- undergoes disproportionation reaction in acidic medium but MnO₄^- does not. Give reason.

Generic 5

7 x 5 = 35

44.

Balance the following equation by oxidation number method.
KMnO₄ + HCI \(\rightarrow\) KCl + MnCl₂ + H₂O + Cl₂

45.

Balance the following equation by oxidation number method.
C₆H₆ + O₂\(\rightarrow\)CO₂ + H₂O

46.

Balance the following equations by oxidation number method.
K₂Cr₂O₇ + FeSO₄ + H₂SO₄ ⟶ K₂SO₄ + Cr₂(SO₄)₃ + Fe₂(SO₄)₃ + H₂O

47.

Balance the following equations by oxidation number method.
NH₃ + F₂ ⟶ HF + N₂

48.

Balance the following equations by ion electron method
\(Zn+{ NO }_{ 3 }^{ - }\longrightarrow { Zn }^{ 2+ }+No\)

49.

In a reaction, A + B₂ \(\longrightarrow \) AB₂, identify the limiting reagent if any in the following reaction mixtures
(i) 300 atoms of A + 200 molecules of B
(ii) 2 moles of A + 3 moles of B
(iii) 100 atoms of A + 100 molecules of B
(iv) 5 moles of A + 2.5 moles of B
(v) 2.5 moles of A + 5 moles of B

50.

Distinguish between the following.
(i) Atomic and molecular mass
(ii) Atomic mass and atomic weight
(iii) Empirical and molecular formula
(iv) Moles and molecules.

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Answers Key:

Multiple Choice Question

14 x 1 = 14

(b)
only (ii)

(a)
Solids

(a)
sublimation

(a)

A B C D

2 3 4 1

(d)
1,2, & 3

(d)
2Ag_(s) + cu²⁺_(aq) \(\longrightarrow\) 2Ag⁺_aq + Cu_(s)

(b)
PbS + 4H₂O₂ \(\longrightarrow\) PbSO₄ + 4H₂O

(a)
-2 to 0, +4 to 0

10.

(a)
CrO₂Cl₂

11.

(d)

A B C D

4 1 2 3

12.

13.

(b)
only (iv)

14.

Assertion and reason

1 x 2 = 2

15.

(a) both assertion and reason are true and the reason is the correct explanation of assertion

Generic 2

10 x 2 = 20

16.

Molar Mass of ferrous Sulphate = \(\begin{cases} atomic\ \ mass\ of\ Fe+atomic\ mass\ of\ s' \\ +4x\ atomic\ mass\ of\ O\ \end{cases}\)
= 56 + 32 + 4 x 16 = 152
In reactions, Fe⁺² ion is oxidised to Fe⁺³ ion Fe⁺² \(\rightarrow\) Fe⁺³ + e
equivalent mass = \(\frac { Molar\quad mass }{ no\quad of\quad involved } =\frac { 152 }{ 1 } =152g{ eq }^{ -1 }\)

17.

molar mass of crystalline oxalic acid (H₂C₂O₄.2H₂o) = Molar Mass of ocalic acid + 2 x Molar mass of H₂o
= 90 + 2 x 18 = 126
Bascity = 2
\(\therefore\) \(\begin{matrix} W\ equivalent\ \ mass\ of \\ crystalline\ \ oxalic\ \ acid \end{matrix}\} =\frac { 126 }{ 2 } =63g\) eq^-1

18.

Molar mass of oxalic acid (H₂C₂O₄) = 2 x 1 + 2 x 12 + 4 x 16 = 90
Basicity of oxalic acid = 2
Equivalent Mass = \(\frac { 90 }{ 2 } =45g\) eq^-1

19.

Molar mass of HNO₃ = 1 + 14 + 3 x 16 = 63
Basicity of HNO₃ = 1
Equivalent mass of HNO₃ = \(\frac { 63 }{ 1 } =63g\) eq^-1

20.

Molar Mass of HCl = 1 + 35.5 = 36.5
Basicity of HCl = 1
\(\therefore\) equivalent mass of hcl = \(\frac { 36.5 }{ 1 } =36.5g\) eq^-1

21.

Number of mole =\(Weight \ of \ the \ substance \ in \ g \over gram \ atomic \ mass (or) \ gram \ molecular \ mass \)

22.

23.

The mass of an atom (10^-27 kg) is too small to be measured directly. They are measured with reference to a standard atom, Hence they are called as relative atomic masses.

24.

(i) Matter can be classified as solids, liquids and gases based on their physical state.
(ii) Matter can also be classified into mixtures and pure substances based on chemical composition.

25.

Mol.mass = 2(H) + 1(S) + 4(0)
= 2(1) + 1(32) + 4(16)
= 2 + 32 + 64 = 98

Generic 3

18 x 3 = 54

26.

Molar mass of NH₃= (1 x 14 + 3 x 1) = 17g mol^-1
Mass of 0.2 mol of NH₃ = 0.2 mol x 17g mol^-1
= 3.4 g

27.

Molecular mass of water = (2 x 1u) + (1 x 16u)
= 18 u
Molar mass of water = 18 g mol^-1
Mass of 1 molecule of water
= \(\frac { Molar\ mass\ of\ water }{ Avogadro's\ number } \)
= \(\frac { 18\ g\ { mol }^{ -1 } }{ 6.023\times { 10 }^{ 23 }\ { mol }^{ -1 } } \)
= 2.99 x 10^-23 g
Mass of 1 molecule of water = 2.99 x 10^-23 g

28.

Molecular mass of silver (Ag) = 107.87 u
Molar mass of Ag = 107.87 g mol^-1
\(\therefore\) Mass of 1 atom of Ag = \(\frac { Molar\ mass }{ Avogadro's\ number } \)
= \(\frac { 107.87g\ { mol }^{ -1 } }{ 6.023\times { 10 }^{ 23 }\ { mol }^{ -1 } } \)
= 17.91 x 10^-23g
Mass of 1 atom of Ag = 17.91 x 10^-23 g.

29.

52g of He contains 7.83 x 10²⁴ He atoms.
1 mol of He contains 6.023 x 10²³ He atoms
\(\therefore\) 52 moles of He contains = \(\frac { 6.023\times { 10 }^{ 23 }\times 52 }{ 1} \)
= 3.132 x 10²⁵
52 moles of He contains 3.132 x 10²⁵ He atoms

30.

Chemical Classification:
1) Matter can be classified into mixtures and pure substances based on chemical compositions.
2 ) Mixtures consist of more than one chemical entity present without any chemical interactions. They can be further classified as homogeneous or heterogeneous mixtures based on their physical appearance
3) Pure substances are composed of simple atoms or molecules. They are further classified as elements and compounds.
(a) Element:
1) An element consists of only one type of atom.
2) Element can exist as monatomic or polyatomic units. The polyatomic elements are called molecules
3) Eg: Monatomic unit - Gold (Au), Copper (Cu); Polyatomic unit- Hydrogen (H₂)
(b) Compound:
1) Compounds are made up of molecules which contain two or more atoms of different elements.
2) Properties of compounds are different from those of their constituent elements.
3) Eg: Carbon dioxide (CO₂), Glucose (C₆H_I2O₆)

31.

Physical Classification of Matter : Matter can be classified as solids, liquids and gases based on their physical state. The physical state of matter can be converted into one another by modifying the temperature and pressure suitably.

32.

	ELEMENTS	COMPOUNDS
(i)	An element consists of only one type of atom	Compounds are made up of molecules which contain two or more atoms of different elements.
(ii)	Element can exist as monatomic or polyatomic units. The polyatomic elements are called molecules	Properties of compounds are different from those of their constituent elements.
(iii)	Eg : Monatomic unit - Gold (Au), Copper (Cu); Poly atomic unit - Hydrogen (H₂)	Eg: Carbon dioxide (CO2), Glucose (C₆H₁₂O₆)

33.

34.

Compound

35.

Air sometimes considered as a heterogeneous mixture due to the presence of dust particles which form a separate phase.

36.

Distilled water molecules contain only H₂O It is a pure substance so a compound. Tap water usually contain impurities such as dust so it is a mixture

37.

'X' is a mixture since elements and compounds are pure substance.

38.

The oxidation state of CI in ClO₂^- is +3. So, chlorine can get oxidised as well as reduced and can act as reductant and oxidant.
The disproportionation reaction of ClO₂^- is
\(\begin{matrix} +1 \\ 3Cl{ O }_{ 2 }^{ - } \end{matrix}\longrightarrow { Cl }^{ - }+\begin{matrix} +5 \\ Cl{ O }_{ 3 }^{ - } \end{matrix}\)
In CIO₄^- , CI is in its highest oxidation state, So it can only be an oxidant.

39.

1. The blue colour of CuSO₄ solution will get discharged and reddish brown copper metal will be deposited on Zn rod.
2. This is because blue colour Cu²⁺ (in CuSO₄) gets reduced to Cu by accepting two electrons from Zn, which gets oxidised to colourless ZnSO₄.

40.

In a redox reaction, the total number of electrons lost by the reducing agent must be equal to the number of electrons gained by the oxidising agent.

41.

1. If H⁺ any acid appears on either side of the chemical equation, the reaction occurs in acidic solution.
2. If OH^- or any base appears on either side of the chemical equation, the reaction occurs in basic solution.
3. If neither H⁺, OH^- nor any acid or base is present in the chemical equation, the solution is neutral.

42.

(i) Oxygen is being added to Cu, (ie.,) Cu₂S is oxidised to Cu₂O and the other reactant O₂ is getting reduced
(ii) Cu₂S is the reducing agent.
O₂ is an oxidising agent.

43.

In MnO₄^2-, Mn is in the highest oxidation state (ie) +7. Therefore, it does not undergo disproportionation. MnO₄^2- undergoes disproportionation as follows :
3MnO₄^2- +4H⁺\(\longrightarrow\) 2MnO₄^-+ MnO₂ + 2H₂O
In MnO₄^2-, the oxidation state of Mn is +6. It can disproportionate to form MnO₂ and MnO₄

Generic 5

7 x 5 = 35

44.

(ii) 2KMnO₄ + 10 HCI \(\rightarrow\) KCl + MnCl₂ + H₂O + Cl₂
(iii) Balance the equation atomically (except O and H).
2KMnO₄ + 10 HCI \(\rightarrow\) 2KCl + 2MnCl₂ + H₂O + Cl₂
(iv) Balance chlorine atoms by adding HCI and multiplying Cl₂ by 5.
2KMnO₄ + 16HCI \(\rightarrow\) 2KCl + 2MnCl₂ + H₂O + 5Cl₂
(v) To balance O and H, H₂O is multiplied by 8.
2KMnO₄ + 16HCI \(\rightarrow\) 2KCl + 2MnCl₂ + 8 H₂O + 5Cl₂

45.

(ii) Balance the changes in O.N. by multiplying the oxidant and reductant by suitable numbers
2 C₆H₆ + 15 O₂\(\rightarrow\)CO₂ + H₂O
(iii) Balance the equation atomically (except O and H).
2 C₆H₆ + 15 O₂\(\rightarrow\)12 CO₂ + H₂O
(iv) Balance O atoms by adding one H₂O molecule to the RHS for making the number of molecules of H₂O to be 6.
2 C₆H₆ + 15 O₂\(\rightarrow\)12 CO₂ + 6 H₂O

46.

Step-1: To find out atoms undergoing change in O.N.
\(\overset { +1+6-2 }{ { K }_{ 2 }{ Cr }_{ 2 }{ O }_{ 7 } } +\overset { +1+6-2 }{ { H }_{ 2 }SO_{ 4 } } +\overset { +2+6-2 }{ Fe{ SO }_{ 4 } } \rightarrow \overset { +1+6-2 }{ { K }_{ 2 }{ SO }_{ 4 } } +\overset { +3\quad \quad +6-2 }{ { Cr }_{ 2 }(SO_{ 4 })_{ 3 } } +\overset { +3\quad \quad +6-2 }{ { Fe }_{ 3 }({ SO }_{ 4 })_{ 3 } } +\overset { +1-2 }{ { H }_{ 2 }O } \)
Step-2: To find out totel increase and decrease in O.N.
\(\overset { +6 }{ { K }_{ 2 }{ Cr }_{ 2 }{ O }_{ 7 } } \rightarrow \overset { +3 }{ { Cr }_{ 2 }({ SO }_{ 4 }) } _{ 3 }\) (Decrease of 3 unit / atom; 6 unit / 2 atoms)
Total decrease = 6 units
\(\overset { +2 }{ Fe_{ 2 }{ SO }_{ 4 } } \rightarrow \overset { +3 }{ { Fe }_{ 2 }({ SO }_{ 4 })_{ 3 } } \) (increase of 1 unit / atom
Total increase 1 x 6 = 6
Step-3: To balance the total increase and total decrease, multiply FeSO₄ by 6.
K₂Cr2O₇ + 6FeSO₄ +H₂SO₄ ⟶ K₂SO₄ + Fe₂(SO₄)₃ + Cr₂(SO₄)₃ + H₂O
Step-4: Balance all atoms other than 'H' and 'O'.
Since Fe is oxidised (LHS) to Fe⁺³ (RHS) balance Fe₂(SO₄)₃ by multiplying by 3.
Now the equation becomes,
K₂Cr₂O₇ + 6FeSO₄ + H₂SO₄ ⟶ K₂SO₄ + Cr₂(SO₄)₃ + 3Fe₂(SO₄)₃ + H₂O
The sulphur atoms in SO₄-² radical does not undergo any change in O.N.
There are 7, SO₄^-2radicals in LHS and 13, SO₄-² radicals in RHS.
To balance them, multiply H₂SO₄ in LHS by 7. The equation now becomes.
K₂Cr₂O₇ + 6FeSO₄ + 7H₂SO₄ ⟶ K₂SO₄ + Cr₂(SO₄)₃ + 3Fe₂(SO₄)₃ +H₂O.

47.

Step - 1 : To find atoms undergoing change in O.N.
\(\overset { +3 }{ { NH }_{ 3 } } +\overset { 0 }{ { F }_{ 2 } } \rightarrow \overset { -1 }{ HF } +\overset { 0 }{ { N }_{ 2 } } \).
Step - 2 : To find the total increase and decrease in O.N.
NH₃ ⟶ N₂ (decrease of 3 units per atom)
F₂ ⟶ HF (increase in 1 unit per atom)
Total decrease = 6 units (3 x 2)
Total increase =6 units (2 x 3)
Step-3: To balance the increase and decrease in O.N, multiply NH₃ by 2 and F₂ by 3.
2NH₃ + 3F₂ ⟶ HF + N₂
Step-4: To balance all atoms other than oxygen
2NH₃ + 3F₂ ⟶ 6HF + N₂
Hydrogen atom balanced by themselves.
Hence, the balanced equation is 2N₃ + 3F₂ ⟶ 6HF + N₂.

48.

\(\overset { o }{ Z } n\longrightarrow { Z }n^{ 2+ }\)
\(\overset { +5 }{ N } { O }_{ 3 }^{ - }\longrightarrow \overset { 2+ }{ NO } \)
(1) \(\Rightarrow \) Zn \(\rightarrow\) Zn²⁺ +2e^- .....(3)
(2) \(\Rightarrow \) \({ NO }_{ 3 }^{ - }+{ 3e }^{ - }+{ 4H }^{ + }\longrightarrow NO+{ 2H }_{ 2 }O\)......(4)

49.

The given equation shows that 1 mole of A reacts with 1 mole of B₂ and I atom of A reacts with 1 molecule of B₂
(i) B is the limiting reagent because 200 molecules of B₂ will react with 200 atoms of A and 100 atoms of A will be left in excess.
(ii) A is limiting reagent because 2 moles of A will react with 2 moles of B and 1 mole of B will be left in excess.
(iii) Both will react completely because it is a stoichiometric mixture. No limiting reagent.
(iv) 2.5 moles of B will react with 2.5 moles of A. Hence B is the limiting reagent.
(v) 2.5 moles of A will react with 2.5 moles of B. Hence A is the. limiting reagent.

50.

(i)	Atomic Mass	Molecular Mass
	Atomic mass is the mass of a single atom, which is its collective mass of neutron proton and electrons	Molecular weight is the mass of one molecule Molecular mass can be calculated from the sum of atomic masses of all atoms present in a compound.
(ii)	Atomic Mass	Atomic Mass
	Atomic mass is the mass of a single atom, which is its collective mass of neutron, proton and electrons	Atomic weight is the average weight of an elements with respect to all its isotopes and their relative abundance.
(iii)	Empricial Formula	Molecular Formula
	It represents the simplest whole number ratio of various atoms present in one molecule of the compound. Empirical formula of Benzene is CH	The molecular formula shows the exact number of different types of atoms present in a molecule of a compound. Molecular formula of Benzene is C₆H_6.
(iv)	Moles	Molecules
	The amount of the substance that contains specified particles as the number of atoms in 12 g carbon - 12 isotope	Two or more atoms joint together by chemical bonds.