Some Basic Concepts of Chemistry JEE JEE Main| JEE Main Important Questions

Q 1 :

0.05 cm thick coating of silver is deposited on a plate of 0.05 $m^{2}$ area. The number of silver atoms deposited on plate are _________ $\times 10^{23}$ . (At mass Ag = 108, d = 7.9 g $c m^{- 3}$ ) [2024]

0%

(11) Volume of silver = thickness $\times$ area of plate

= 0.05 cm $\times$ 0.05 $m^{2}$

= 0.05 cm $\times$ 0.05 $\times$ ${(100 c m)}^{2}$

= 25 $c m^{3}$

Mass of silver deposited = density $\times$ volume

= 7.9 $g c m^{- 3} \times$ 25 $c m^{3}$

= 197.5 g

Moles of silver deposited(n) = $\frac{M a s s o f s i l v e r d e p o s i t e d}{m o l a r m a s s o f s i l v e r}$

= $\frac{197.5 g}{108 g m o l^{- 1}}$

= 1.8287 mol

Atoms of silver deposited = $n \times N_{A}$ atoms

= 1.8287 $\times$ 6.022 $\times 10^{23}$

= 11.01 $\times 10^{23}$ atoms

Q 2 :

$2.8 \times 10^{- 3}$ mol of ${CO}_{2}$ is left after removing $10^{21}$ molecules from its $‘ x ’$ mg sample. The mass of ${CO}_{2}$ taken initially is

Given: $N_{A} = 6.02 \times 10^{23} {mol}^{- 1}$ [2025]

48.2 mg
98.3 mg
150.4 mg
196.2 mg

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4

(4)

$10^{21} molecules = \frac{10^{21}}{6.02 \times 10^{23}} mol = 1.66 \times 10^{- 3} mol$

Initial moles = mole left + mole removed

Initial moles $= 2.8 \times 10^{- 3} mol + 1.66 \times 10^{- 3} mol$

$= 4.46 \times 10^{- 3} mol$

$Initial mass = Initial moles \times molar mass$

$= 4.46 \times 10^{- 3} mol \times 44 {g mol}^{- 1}$

$= 196.24 \times 10^{- 3} g = 196.24 mg$

Q 3 :

Among $10^{- 9}$ g (each) of the following elements, which one will have the highest number of atoms?

Element: Pb, Po, Pr and Pt [2025]

Po
Pr
Pb
Pt

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4

(2)

$Number of atoms = \frac{Given mass}{Atomic mass}$

As given mass is same for the four elements,

$number of atoms \propto \frac{1}{Atomic mass} .$

Po and Pb are present in 6th period, p block. Pt is present in 5d series. Pr is present in 4f series. As Pr is placed before Po, Pb and Pt in periodic table, it has least atomic mass. As it has least atomic mass, it has most number of atoms.

Q 4 :

The number of molecules and moles in $2.8375 litres$ of $O_{2}$ at STP are respectively [2023]

$7.527 \times 10^{22}$ and $0.125 mol$
$1.505 \times 10^{23}$ and $0.250 mol$
$7.527 \times 10^{23}$ and $0.125 mol$
$7.527 \times 10^{22}$ and $0.250 mol$

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(1)

$No. of moles = \frac{Volume at S.T.P (L)}{22.4} = \frac{2.8375}{22.4} = 0.125 mole$

$No. of molecules = no. of moles \times N_{A}$

$= 0.125 \times 6.023 \times 10^{23}$

$= 7.527 \times 10^{22}$

Q 5 :

Match List I with List II. [2023]

List I List II

A. 16 g of ${CH}_{4} (g)$ I. Weighs 28 g

B. 1 g of $H_{2} (g)$ II. $60.2 \times 10^{23}$ electrons

C. 1 mole of $N_{2} (g)$ III. Weighs 32 g

D. 0.5 mol of ${SO}_{2} (g)$ IV. Occupies 11.4 L volume at STP

Choose the correct answer from the options given below:

A-II, B-IV, C-III, D-I
A-I, B-III, C-II, D-IV
A-II, B-III, C-IV, D-I
A-II, B-IV, C-I, D-III

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(4)

(A) $16 g or 1 mol C H_{4} or 6.02 \times 10^{23} \times 10 electrons$

$= 60.2 \times 10^{23} electrons (II)$

(B) ${1 g H}_{2} or \frac{1}{2} mol H_{2} or 11.35 L volume at STP (IV)$

(C) $1 mol N_{2} = 28 g N_{2} (I)$

(D) $0.5 mol S O_{2} = 32 g S O_{2} (III)$

Topic Question Set

Q 1 :

0.05 cm thick coating of silver is deposited on a plate of 0.05 $m^{2}$ area. The number of silver atoms deposited on plate are _________ $\times 10^{23}$ . (At mass Ag = 108, d = 7.9 g $c m^{- 3}$ ) [2024]

0%

Q 2 :

$2.8 \times 10^{- 3}$ mol of ${CO}_{2}$ is left after removing $10^{21}$ molecules from its $‘ x ’$ mg sample. The mass of ${CO}_{2}$ taken initially is

Given: $N_{A} = 6.02 \times 10^{23} {mol}^{- 1}$ [2025]

Q 3 :

Among $10^{- 9}$ g (each) of the following elements, which one will have the highest number of atoms?

Element: Pb, Po, Pr and Pt [2025]

Q 4 :

The number of molecules and moles in $2.8375 litres$ of $O_{2}$ at STP are respectively [2023]

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	List I		List II
A.	16 g of ${CH}_{4} (g)$	I.	Weighs 28 g
B.	1 g of $H_{2} (g)$	II.	$60.2 \times 10^{23}$ electrons
C.	1 mole of $N_{2} (g)$	III.	Weighs 32 g
D.	0.5 mol of ${SO}_{2} (g)$	IV.	Occupies 11.4 L volume at STP