Important questions -chapter 1,2

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Questions:

Generic 5

8 x 5 = 40

\({ 2NH }_{ 3 }\left( g \right) +{ CO }_{ 2 }\left( g \right) \rightarrow \underset{Urea}{H_2N}-\overset { \underset { || }{ O } }{ C } -{ NH }_{ 2 }\left( aq \right) +{ H }_{ 2 }O(I)\)
In a process, 646 g of ammonia is allowed to react with 1.144 kg of CO₂ to form urea.
(i) If the entire quantity of all the reactants is not consumed in the reaction which is the limiting reagent ?
(ii) Calculate the quantity of urea formed and unreacted quantity of the excess reagent. The balanced equation is
\(\overset { { 2NH }_{ 3 }+{ CO }_{ 2 } }{ \underset { { H }_{ 2 }NCON{ H }_{ 2 }+{ H }_{ 2 }O }{ \downarrow } } \)

Calculate the percentage composition of the elements present in magnesium carbonate. How many kilogram of CO₂ can be obtained by heating 1 kg of 90 % pure magnesium carbonate.

Balance the following equation by oxidation number method:
P + HNO₃ \(\rightarrow\)H₃PO₄+ NO₂ + H₂O

Balance the following equations by oxidation number method.
KMnO₄ + KOH + H₂O₂ ⟶ K₂MnO₄ + O₂ + H₂O

Balance the following equations by ion electron method.
i) \({ KMn }O_{ 4 }+{ SnCl }_{ 2 }+HCI\longrightarrow MnCI_{ 2 }+{ SnCI }_{ 4 }+{ H }_{ 2 }O+KCI\)
ii)
iii)
iv)

Calculate the uncertainty in position of a dust particle of mass 0.1 mg if the uncertainty in velocity is \(5\times { 10 }^{ -19 }{ ms }^{ -1 }\)

Define orbital ? what are the n and 1 values for 3p_x and 4d_x²_-_y² electron ?

By applying Bohr's postulates, arrive at the radius of n^th orbit for hydrogen like atom

Multiple Choice Question

5 x 1 = 5

The empirical formula of glucose is __________

(a)

(b)

CH₂O

(c)

CH₂O₂

(d)

CHO

10.

The oxidation number of fluorine in all its compounds is equal to ______________.

(a)

-1

(b)

(c)

-2

(d)

11.

Which of the following is the actual configuration of Cr (Z = 24)?

(a)

1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁴ 4s²

(b)

1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s¹

(c)

1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶

(d)

1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s³

12.

What will be the wavelength of a ball of mass 0.1 kg moving with a velocity of 10ms^-1?

(a)

6.62 \(\times\) 10^-34m

(b)

6.626 \(\times\) 10³⁴m

(c)

6.626 \(\times\) 10^-34m

(d)

6.626 \(\times\) 10³⁴m

13.

The maximum number of electrons in a sub shell is given by the expression _____________

(a)

2n²

(b)

2l + 1

(c)

4l + 2

(d)

none of these

Assertion and reason

1 x 2 = 2

14.

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 3

6 x 3 = 18

15.

Calculate the de Broglie wavelength of an electron moving with 1% of the speed of light?

16.

Calculate the mass of the following atoms in a.m.u (unified atomic mass).

17.

Calculate the number of atoms/molecules present in the following 100 g of sulphur dioxide

18.

The percentage of all the elements present o in a compound is 95. What does it indicate?

19.

Show that if the measurement of the uncertainty in the location of the particle is equal to its de Broglie wavelength, the minimum uncertainty in its velocity is equal to its velocity 1/4\(\pi\) of its velocity (V).

20.

An atom having atomic mass number 13 has 7 neutrons. What is the atomic number of the atom?

Generic 2

5 x 2 = 10

21.

How many electrons can be accommodated in the main shell I,m and n?

22.

Which ion has the stable electronic configuration? Ni²⁺ or Fe³⁺.

23.

Calculate the equivalent masses of the following - Oxalic acid H₂C₂O₄

24.

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

25.

What is the difference between atomic mass and mass number?

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Answers Key:

Generic 5

8 x 5 = 40

(i) The entire quantity of ammonia is consumed in the reaction. So ammonia is the Iimiting reagent. Some quantity of CO₂ remains unreacted, so CO₂ is the excess reagent.
(ii) Quantity of urea formed = number of moles of urea formed x molar mass of urea
= 19 moles x 60 g mol^-1
= 1140 g = 1.14 kg
Excess reagent leftover at the end of the reaction is carbon dioxide.
Amount of carbon dioxide leftover
= number of moles of CO₂left over x molar mass of CO₂
= 7 moles x 44 g mol^-1
= 308 g

	Reactants		Products
	NH₃	CO₂	Urea	H₂O
Stoichiometric coefficients	2	1	1	1
Number of moles of reactants allowed to react \(N=\frac { Mass }{ Molar\quad mass } \)	\(\frac { 646 }{ 17 } =38\) moles	\(\frac { 1144 }{ 44 } =26\)moles	-	-
Actual number of moles consumed during reaction Ratio (2:1)	38 moles	19 moles	-	-
No.of moles of product thus formed	-	-	19 moles	19 moles
No.of moles of reactant left at the end of the reaction	-	7 moles	-	-

The balanced chemical equation is
\(\mathrm{MgCO}_{3} \stackrel{\Delta}{\longrightarrow} \mathrm{MgO}+\mathrm{CO}_{2}\)
Molar mass of MgCO₃ is 84 g mol^–1.
84 g MgCO₃ contain 24 g of Magnesium.
∴ 100 g of MgCO₃ contain

= 28.57 g Mg.
i.e. percentage of magnesium
= 28.57 %.
84 g MgCO₃ contain 12 g of carbon

∴ 100 g MgCO₃ contain

= 14.29 g of carbon.
∴ Percentage of carbon
= 14.29 %.
84 g MgCO₃ contain 48 g of oxygen
∴ 100 g MgCO₃ contains

= 57.14 g of oxygen.
∴ Percentage of oxygen
= 57.14 %.
As per the stoichiometric equation,
84 g of 100 % pure MgCO₃ on heating gives 44 g of CO_2.
∴ 1000 g of 90 % pure MgCO₃ gives
\(\frac{\text { wt. of } \mathrm{MgCO}_{3}}{84 \mathrm{~g}} \frac{\text { % Purities }}{100 \%} \frac{\text { wt.of } \mathrm{CO}_{2}}{44 \mathrm{~g}}\)
\(x=44 \times \frac{100}{84} \times \frac{90}{100}\)
= 471.43 g CO₂
= 0.471 kg CO₂

Step 2. P + 5HNO₃ \(\rightarrow\)H₃PO₄+5 NO₂ + H₂O

Step - 1 : To find out atoms undergoing change in O.N.
\(\overset { +1+7-2 }{ KMnO_{ 4 } } +\overset { +1-2+1 }{ KOH } +\overset { +1-1 }{ { H }_{ 2 }{ O }_{ 2 } } \rightarrow +\overset { +1+6-2 }{ K_{ 2 }MnO_{ 4 } } +\overset { 0 }{ { O }_{ 2 } } +\overset { +1-2 }{ { H }_{ 2 }O } \)
Step - 2 : To find out total increase and decrease in O.N .
\(\overset { +7 }{ KMnO_{ 4 } } \rightarrow \overset { +6 }{ K_{ 2 }MnO_{ 4 } } \) (decrease of 1 unit per atom)
\(\overset { -1 }{ { H }_{ 2 }{ O }_{ 2 } } \rightarrow \overset { 0 }{ { O }_{ 2 } } \) (increase of 1 unit per atom or 2 units per atom)
Total increase = 2
Total decrease = 2
Step - 3 : To balance the total increase and decrease in O.N, multiply KMnO₄ by 2.
2KMnO₄ + KOH + H₂O₂ ⟶ K2MnO₄ + O₂ + H₂O
Step - 4 : To balance all atoms other than 'H' and 'O'
2KMnO₄ + 2KOH + H₂O₂ ⟶ 2K₂MnO₄ + O₂ + H₂O
number of oxygen atoms on LHS = 12
number of oxygen atoms on RHS = 11
Hence, multiply H₂O in RHS by 2. The equation becomes,
2KMnO₄ + 2KOH + H₂O₂ ⟶ 2K₂MnO₄ + O₂ + H₂O
Hydrogen atoms balance by themselves. The balanced equation is
2KMnO₄ + 2KOH + H₂O₂ ⟶ 2K₂MnO₄ + O₂ + 2H₂O

Half reactions are:
\(\overset { +7 }{ M } { nO }_{ 4 }^{ - }\longrightarrow { Mn }^{ 2+ }\)
and \({ Sn }^{ 2+ }\longrightarrow { Sn }^{ 4+ }\)
(1) \(\Rightarrow \) \({ MnO }_{ 4 }^{ - }+{ 8H }^{ - }+5e^{ - }\longrightarrow { Mn }^{ 2+ }+{ 4H }_{ 2 }O\)
(2) \(\Rightarrow \) \({ Sn }^{ 2+ }\longrightarrow { Sn }^{ 4+ }+{ 2e }^{ - }\)

ii)

iii)

iv)

h = \(6.626\times { 10 }^{ -34 }kg{ m }^{ 2 }{ s }^{ -1 }\)
m = 0.1 mg = 1 X 10^-7 kg
Δv =\(5\times { 10 }^{ -19 }{ ms }^{ -1 }\)
Uncertainty in position
\(\Delta x=\frac { h }{ 4\pi m\Delta v } \)
= \(\frac { 6.626\times { 10 }^{ -34 }kg{ m }^{ 2 }{ s }^{ -1 } }{ 4\times 3.143\times { 10 }^{ -7 }kg\times 5\times { 10 }^{ -9 }{ ms }^{ -1 } } \)
= \(1.05\times { 10 }^{ -9 }m\)
\(\boxed{\triangle x=1.05\ nm}\)

The solution to Schrodinger equation gives the permitted total energy values called eigen values and the corresponding wave function represent atomic orbitals.

Orbital	n	l
3p_x	3	1
4d_x²_-_y²	4	2

Applying Bohr's postulates to a hydrogen like atom (one electron species such as H, He⁺ and Li²⁺ etc...)the radius of the n^th orbit and the energy of the electron revolving in the n^th orbit were derived. The results are as follows:
r_n = \(\frac { (0.529){ n }^{ 2 } }{ x } \mathring { A } \) ...(1)
E_n= \(\frac { -13.6({ z }^{ 2 }) }{ { n }^{ 2 } } ev\quad { atom }^{ -1 }\) or ... (2) or
E_n = \(\frac { (-1312.8){ z }^{ 2 } }{ { n }^{ 2 } } kJ\quad { mol }^{ -1 }\) .....(3)

Multiple Choice Question

5 x 1 = 5

(b)
CH₂O

10.

(a)
-1

11.

(b)
1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s¹

12.

(a)
6.62 \(\times\) 10^-34m

13.

Assertion and reason

1 x 2 = 2

14.

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

Generic 3

6 x 3 = 18

15.

According to de Broglie equation, \(\lambda ={h\over mv}\)
Mass of electron = 9.1 x 10^-31kg; Planck's constant = 6.626 x 10^-34kg m² s^-1
Velocity of electron = 1% of speed of light = 3.0 x 10⁸ x 0.01 = 3 x 10⁶ ms^-1
Wavelength of electron(\(\lambda\)) =\(h\over mv\) = \({(6.626\times 10^{-34}kg m^2s^{-1})\over (9.1\times 10^{-31}kg)\times(3\times 10^6ms^{-1})}\)
= 2.43 x 10^-10m.

16.

(i) Oxygen: (average mass of oxygen atom = 2.656 x 1O^-23g
1 a.m.u = 1.6605 x 1O^-27kgor 1.6605 x 1O^-24gram)
(ii) Mass of an oxygen atom = 2.656 x 1O^-23g
The mass of oxygen atom In a.m.u = \({Average \ mass \ of \ oxygen \ atom \ in \ gram\over1.6605\times10^{-24}}\)
\(={2.656\times10^{-23}g\over1.6605 \times 10^{-24}g}\)
= 1.599 x10
= 15.99 a.m.u

17.

Molecular mass of SO₂= 64
64 g of sulphur dioxide contains = 6.023 \(\times\) 10²³
Molecules of SO₂
∴ 100g of SO₂ contains = \(\frac { 100\times 6.023\times { 10 }^{ 23 } }{ 64 } \)
= 9.41
Molecules of SO₂

18.

This indicates that the compound contains oxygen. Its percentage is given as 100 - 95 = 5

19.

\(\triangle x=?\)
\(\triangle v=?\)
\(\triangle x.\triangle p\ge\frac{h}{4\pi}\)
\(\lambda (m\triangle v)\ge\frac{h}{4\pi}\)
\(\triangle v\ge\frac{h}{4\pi(m\lambda)}\)
\(\triangle \ge\frac{h}{4\pi\times m \times\frac{h}{mv}}\) \(\left[ \because \lambda-={{h}\over{mv}} \right]\)
\(\triangle v \ge \frac{v}{4\pi}\)
therefore, minimum uncertainty in velocity \(=\frac{v}{4\pi}\)

20.

A = 13, A - Z = 7 (Neutrons)
Then Z= 6
(ie) Atomic number = 6

Generic 2

5 x 2 = 10

21.

Main shell	l	m	n
Principal quantum number	2	3	4
Number of electrons in the main shell 2n²	2(2)²= 8	2(3)²= 18	2(4)²= 32

22.

Electronic configuration of Fe³⁺ : 1s² 2s² 2p⁶ 3s² 3p⁶ 4s⁰ 3d⁵
Electronic configuration of Ni²⁺ : 1s² 2s² 2p⁶ 3s² 3p⁶ 4s⁰ 3d⁸
Fe³⁺ has stable 3d⁵ half filled configuration.

23.

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

24.

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

25.

(i) Mass number is a whole number because it is the sum of number of protons and number of neutrons.
(ii) Atomic mass is fractional because it is the average relative mass of its atom as compared with mass of an atom of C-12 isotope taken as 12.