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Page # 109
STOICHIOMETRY - 1
Ex.13 An atom of an element weighs 6.644 × 10 –23 g. Calculate g atoms of element i n 40 kg(A) 10 gm atom
Sol.
(B) 100 gm atom
(C) 1000 gm atom
(D) 10 4 gm atom
(C)
wei ght of 1 atom of element
= 6.644 × 10 –23 gm
weight of 'N' atoms of element
= 6.644 × 10–23 × 6.023 × 10 23
= 40 gm
40 gm of element has 1 gm atom.
40 x 10 3 gm of element has
40 103
, = 10 3 gm atom.
40
Ex.14 Calculate the number of Cl – and Ca+2 ions in 222 g anhydrous CaCl 2 -
Sol.
(A) 2N ions of Ca +2 4 N ions of Cl –
(C) 1N ions of Ca +2 & 1N ions of Cl –
(A)
mol. wt. of CaCl 2 = 111 g
111 g CaCl 2 has = N ions of Ca +2
222g of CaCl 2 has
Also
(B) 2N ions of Cl – & 4N ions of Ca +2
(D) None of these.
N 222
111
= 2N ions of Ca +2
111 g CaCl 2 has = 2N ions of Cl –
222 g CaCl 2 has =
2N 222
ions of Cl –
111
= 4N ions of Cl – .
Ex.15 The density of O 2 at NTP is 1.429g / litre. Calcul ate the standard molar volume of gas(A) 22.4 lit.
(B) 11.2 lit
(C) 33.6 lit
(D) 5.6 l it.
Sol.
(A)
1.429 gm of O 2 gas occupies volume = 1 l itre.
32 gm of O 2 gas occupies =
32
,= 22.4 litre/mol.
1429
.
Ex.16 Which of the following will weigh maximum amount(A) 40 g iron
(B) 1.2 g atom of N
(C) 1 × 10 23 atoms of carbon
(D) 1.12 litre of O2 at STP
Sol.
(A)
(A) Mass of iron = 40 g
(B) Mass of 1.2 g atom of N = 14 × 1.2 = 16.8 gm
(D) Mass of 1 × 10 23 atoms of C
(D) Mass of 1.12 litre of O 2 at STP
=
12 1 10 23
= 1.99 gm.
6.023 10 23
32 1 .2
=
= 1.6 g
22 .4
Ex.17 How many mol es of potassi um chlorate to be heated to produce 11.2 li tre oxygen (A)
1
mol
2
(B)
1
mol
3
(C)
1
mol
4
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(D)
2
mol.
3
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