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Questions:

Multiple Choice Question

14 x 1 = 14

The molar mass of Na₂SO₄ is ___________.

(a)

129

(b)

142

(c)

110

(d)

The number of molecules in 16g of methane is _________

(a)

3.023 x 10²³

(b)

6.023 x 10²³

(c)

16/6.023 x 10²³

(d)

6.023/3 x 10²³

How many moles of magnesium phosphate Mg₃(PO₄)₂ Will Contain 0.25 moles of oxygen atoms?

(a)

0.02

(b)

3.125 x 10^-2

(c)

1.25 x 10^-2

(d)

2.5 x 10^-2

Calculate the percentage of N in ammonia molecule.

(a)

121.42%

(b)

28.35%

(c)

82.35%

(d)

28.53%

The energy of electron in an atom is given by En =

(a)

\(\frac { 4{ \pi }^{ 2 }{ me }^{ 4 } }{ { n }^{ 2 }h^{ 2 } } \)

(b)

\(\frac { 2{ \pi }^{ 2 }{ me }^{ 4 } }{ { n }^{ 2 }h^{ 2 } } \)

(c)

\(\frac { 2{ \pi }^{ 2 }{ me }^{ 4 } }{ { n }^{ 2 }h^{ 2 } } \)

(d)

\(\frac { 2{ \pi }{ me }^{ 4 } }{ { n }^{ 2 }h^{ 2 } } \)

Which is the lightest among the following?

(a)

An atom of hydrogen

(b)

An electron

(c)

A neutron

(d)

A proton

Which one of the following is used as a standard for atomic mass?

(a)

₆C¹²

(b)

₇C¹²

(c)

₆C¹³

(d)

₆C¹⁴

The mass of a gas that occupies a volume of 612.5 ml at room temperature and pressure (25⁰ c and 1 atm pressure) is 1.1g. The molar mass of the gas is _______.

(a)

66.25 g mol^-1

(b)

44 g mol^-1

(c)

24.5 g mol^-1

(d)

662.5 g mol^-1

7.5 g of a gas occupies a volume of 5.6 litres at 0° C and 1 atm pressure. The gas is ________.

(a)

(b)

N₂O

(c)

(d)

CO₂

10.

Which one of the following represents 180 g of water ?

(a)

5 Moles of water

(b)

90 moles of water

(c)

\(\frac { 6.022\times { 10 }^{ 23 } }{ 180 } \) molecules of water

(d)

6.022\(\times\)10²⁴molecules of water

11.

The oxidation number of oxygen in O₂ is__________

(a)

(b)

(c)

(d)

-2

12.

Hot concentrated sulphuric acid is a moderately strong oxidizing agent. Which of the following reactions does not show oxidising behaviour ?

(a)

Cu + 2H₂SO₄ \(\longrightarrow \) CuSO₄ +SO₂ + 2H₂O

(b)

C + 2H₂ + SO₄ \(\longrightarrow \) CO₂ + 2SO₂ + 2H₂O

(c)

BaCl₂ + H₂SO₄ \(\longrightarrow \) BaSO₄ + 2HCl

(d)

None of the above

13.

1 g of an impure sample of magnesium carbonate (containing no thermally decomposable impurities) on complete thermal decomposition gave 0.44 g of carbon dioxide gas. The percentage of impurity in the sample is ______________.

(a)

(b)

4.4%

(c)

16%

(d)

8.4%

14.

An element X has the following isotopic Composition ²⁰⁰X = 90%, ¹⁹⁹X = 8% and ²⁰²X=2%.The Weighted average atomic mass of the element X is closest to _________.

(a)

201 u

(b)

202 u

(c)

199 u

(d)

200 u

Generic 2

6 x 2 = 12

15.

What is milk of lime? How CO₂ reacts with it?

16.

Discuss the biological importance of sodium and potassium.

17.

At room temperature, Hydrogen reacts very slowly. Explain

18.

What is the usual definition of entropy? What is the unit of entropy?

19.

Explain whether a gas approaches ideal behavior or deviates from ideal behaviour if
it is compressed to a smaller volume at constant temperature.

20.

What do you understand by the term oxidation number ?

Assertion and reason

1 x 2 = 2

21.

Assertion (A): In the reaction between potassium permanganate and potassium iodide, permanganate ions act as oxidising agent.
Reason (R): Oxidation state of manganese changes from +2 to +7 during the reaction.
Codes:
(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

(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 3

6 x 3 = 18

22.

Energy of an electron in hydrogen atom in ground state is -13.6 eV. What is the energy of the electron in the second excited state?

23.

0.456 g of a metal gives 0.606 g of its chloride. Calculate the equivalent mass of the metal.

24.

State the various statements of second law of thermodynamics.

25.

A sample of gas at 15°C at 1 atm. has a volume of 2.58 dm³. When the temperature is raised to 38°C at 1 atm does the volume of the gas increase? If so, calculate the final volume.

26.

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

27.

Categorise the redox reactions that occur in our daily life

Generic 5

5 x 5 = 25

28.

Balance the following equations by oxidation number method.
P + HNO₃ ⟶ HPO₃ + NO + H₂O

29.

Give the structural features of modern periodic law.

30.

A Compound on analysis gave Na = 14.31% S = 9.97% H = 6.22% and 0 = 69.5%.
Calculate the molecular formula of the compound if all the hydrogen in the compound is present in combination with oxygen as a water of crystallization. (molecular mass of the compound is 322).

31.

Calculate the empirical and molecular formula of a compound containing 76.6% carbon, 6.38 % hydrogen and rest oxygen its vapour density is 47.

32.

What is screening effect? Briefly give the basis for pauling's scale of electronegativity.

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Answers Key:

Multiple Choice Question

14 x 1 = 14

(b)
142

(b)
6.023 x 10²³

(b)
3.125 x 10^-2

(b)
An electron

(a)
₆C¹²

(b)
44 g mol^-1

(a)
NO

10.

(d)
6.022\(\times\)10²⁴molecules of water

11.

(a)
0

12.

13.

14.

(d)
200 u

Generic 2

6 x 2 = 12

15.

The aqueous solution of calcium hydroxide is known as lime water and a suspension of slaked lime in water is known as milk of lime. When carbon dioxide is passed through lime water, it turns milky due to the formation of calcium carbonate.
\(Ca(OH)_2 + CO_2 ⟶ CaCO_3 + H_2O\)

16.

(i) Sodium and potassium ions maintain the ion balance and nerve impulse conduction.
(ii) Transport of sugar and amino acids into cells.
(iii) Potassium ions activate many enzymes, participate in the oxidation of glucose to produce ATP.
(iv) With sodium, potassium ion is responsible for the transmission of nerve signals.
(v) Sodium and potassium pump play an important role in transmitting nerve signals.

17.

In elementary state, Hydrogen exists as a diatomic molecule. The bond between two hydrogen atoms H-H is covalent. The bond dissociation energy is very high (435.9 Klmol-1 ). So bond cleavage is extremely difficult, so hydrogen is less reactive at room temperature.

18.

(i) Entropy is a measure of the molecular disorderliness (randomness) of a system. dS = dq_rev/T
(ii) The entropy (S) is equal to heat energy exchanged (q) divided by the temperature (T) at which the exchange takes place. Therefore, The SI unit of entropy is JK^-1

19.

The gas deviates from ideal gas behaviour and will be a real gas only. In the compressed state, the inter molecular forces will be very high as the molecules are very close.

20.

It is defined as the imaginary charge left on the atom when all other atoms of the compound have been removed in their usual oxidation states that are assigned according to set of rules.

Assertion and reason

1 x 2 = 2

21.

Generic 3

6 x 3 = 18

22.

\(\mathrm{E}_{n}=\frac{-13.6}{\mathrm{n}^{2}} \mathrm{eV}\)
Second excited state
\(\therefore E_{3}=\frac{-13.6}{9} \mathrm{eV}\)
n = 3
E₃ = -1.51 eV

23.

Mass of the metal = 0.456 g
Mass of the metal chloride = 0.606 g
0.456 g of the metal combines with 0.15 g of chlorine.
Mass of the metal that combines with 35.5 g of chlorine is \(\frac{0.456}{0.15}\) x 35.5
= 107.92 g eq^-1.

24.

(i) Kelvin-Planck statement: It is impossible to construct a machine that absorbs heat from a hot source and converts it completely into work by a cyclic process without transferring a part of heat to a cold sink.
(ii) Clausius statement: It is impossible to transfer heat from a cold reservoir to a hot reservoir without doing some work.
(iii) Entropy statement: The entropy of an isolated system increases during a spontaneous process

25.

T₁= 15^oC + 273 T₂= 38 + 273
T₁= 288 K T₂= 311 K
V₁= 2.58 dm³ V₂= ?
(P = 1 atm constant)
\(\frac { { V }_{ 1 } }{ { T }_{ 1 } } =\frac { { V }_{ 2 } }{ { T }_{ 2 } } \)
\({ V }_{ 2 }=\left( \frac { { V }_{ 1 } }{ { T }_{ 1 } } \right) \times { T }_{ 2 }\)

V₂= 2.78 dm³ i.e. volume increased from 2.58 dm³ to 2.78 dm³.

26.

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.

27.

1. Fading of the colour of the clothes
2. Burning of cooking gas, fuel, wood, etc.
3. Rusting of Iron
4. Extraction of Metals

Generic 5

5 x 5 = 25

28.

Step-1: To find atoms undergoing change in O.N
\(\overset { 0 }{ P } +\overset { +1\quad +5 }{ HNO_{ 3 } } \rightarrow \overset { +1+5-2 }{ HPO_{ 3 } } +\overset { +1-2 }{ NO } +\overset { +1-2 }{ { H }_{ 2 }O } \)
Step-2: To find total decrease and increase in O.N.
P ⟶ HPO₃ (increase in O.N. of 5 units per atom)
HNO₃ ⟶ NO (decrease in O.N. of3 units per atom)
Total decrease 5 x 3 = 15
Total increase 3 x 5 = 15
Step-3: To balance the total increase and decrease in the equation, by multiplying P by 3 and HNO₃ by 5.
3P + 5HNO3 ⟶ HPO₃ + NO + H₂O
Step-4: To balance all atoms other than 'O' and 'H'
3P + 5HNO₃ ⟶ 3HPO₃ + 5NO + H₂O
Step-5: To balance by oxygen atoms
Oxygen and hydrogen atoms balance by themselves.
Hence the balanced equation is 3P + 5HNO3 ⟶ 3HPO₃ + 5 NO + H₂O

29.

(i) According to the recommendation of IUPAC, the groups are numbered from 1 to 181A.
(ii) There are 18 vertical columns which constitute 18 groups or families.
(iii) There are 7 horizontal rows of the periodic table known as periods.
(iv) The first period contains two elements. One present in first group and the other in 18th group.
(v) Second and third periods contain 8 elements in each.
(vi) Fourth and fifth periods are completely filled as they contain 18 elements in each.
(vii) The sixth period contains 32 elements. The seventh is incomplete. Fourteen elements of both sixth and seventh periods are placed in separate panels at the bottom of the table.
(viii) This periodic table is important and useful because we can predict the properties of any element using periodic trend.

30.

Element	%	Relative number of atoms	Simple Ratio
Na	14.31	\(\frac { 14.31 }{ 23 } =0.62\)	\(\frac { 0.62 }{ 0.31 } =2\)
S	9.97	\(\frac { 9.97 }{ 32 } =0.31\)	\(\frac { 0.31 }{ 0.31 } =1\)
H	6.22	\(\frac { 6.22 }{ 1 } =6.22\)	\(\frac { 6.22 }{ 0.31 } =20\)
O	69.5	\(\frac { 69.5 }{ 16 } =4.34\)	\(\frac { 4.34 }{ 0.31 } =14\)

Empirical formula = Na₂SH₂₀O₁₄
\(\left[ \begin{matrix} { Na }_{ 2 }{ SH }_{ 20 }{ O }_{ 14 } \\ =(2\times 23)+(1\times 32)+(20\times 1)+14(16) \\ =46+32+20+234 \\ =322 \end{matrix} \right] \)
n = \(\frac { molar\quad mass }{ caluclated\quad empirical\quad formula\quad mass } =\frac { 322 }{ 322 } =1\)
Molecular formula = Na₂ SH₂₀O₁₄
Since all the hydrogen in the compound are present as water
\(\therefore \) The molecular formula is Na₂ SO₄10H₂O.

31.

Element	Percentage	Atomic mass	Relative number of atoms	simple ratio	Whole no
C	76.6	12	\(\frac { 76.6 }{ 12 } =6.38\)	\(\frac { 6.38 }{ 1.06 } =6\)	6
H	6.38	1	\(\frac { 6.38 }{ 1 } =6.38\)	\(\frac { 6.38 }{ 1.06 } =6\)	6
0	17.02	16	\(\frac { 17.02 }{ 16 } =1.06\)	\(1.06\frac { 1.06 }{ 1.06 } =1\)	1

Empirical Formula = C₆H₆O
n = \(\frac { molar\ mass }{ calculated\ eprirical\ formula\ mass } \)
= \(\frac { 2\times \ vapour\ density }{ 94 } \frac { 2\times 47 }{ 94 } =1,\)
Molecular formula (C₆H₆O) x 1 = C₆H₆O.

32.

Screening effect: The repulsive force between the inner shell electrons and the valence electrons leads to a decrease in the electrostatic attractive forces acting on the valence electrons by the nucleus. Thus, the inner shell electrons act as a shield between the nucleus and the valence electrons. This effect is called shielding effect.
Pauling's scale: Pauling, he assigned arbitrary value of electronegativities for hydrogen and fluorine as 2.2 and 4.0 respectively. Based on this the electronegativity values for other elements can be calculated using the following expression.
\(({ X }_{ A }-{ X }_{ B })=0.182\sqrt { E_{ AB } } -({ E }_{ AA }*{ E }_{ BB })^{ 1/2 }\)
Where E_AB' EAA and E_BB are the bond dissociation energies of AB, A₂ and B₂ molecules respectively. The electronegativity of any given element is not a constant and its value depends on the element to which it is covalently bound. The electronegativity values play an important role in predicting the nature of the bond.