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# Download motion sample booklet class xi

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```Page # 126
STOICHIOMETRY - 1
Sol.
43.
Sol.
A graph is plotted for an element, by putting
its weight on X-axis
and the corresponding number of number of
atoms on Y-axis. Determine
the atomic weight of the element for which the
graph is plotted.
47.
Two isotopes of an element Q are Q 97 (23.4%
abundance) and Q94 (76.6% abundance). Q 97
is 8.082 times heavier than C 12 and Q 94 is
7.833 times heavier than C 12. What is the
average atomic weight of the element Q?
(A) 94.702
(B) 78.913
(C) 96.298
(D) 94.695
Sol.
(A) infinite
(C) 0.025
(B) 40
(D) 20
48.
Sol.
44.
The O18/O 16 ratio in some meteorites is greater
than that used to calculate the average atomic
mass of oxygen on earth. The average mass
of an atom of oxygen in these meteorites is
___ that of a terrestrial oxygen atom?
(A) equal to
(B) greater than
(C) less than
(D) None of these
The element silicon makes up 25.7% of the
earth's crust by weight, and is the second
most abundant element, with oxygen being the
first. Three isotopes of silicon occur in nature:
Si 28 (92.21%), which has an atomic mass of
27.97693 amu; Si 29 (4.70%), with an atomic
mass of 28.97649 amu; and Si 30 (3.09%), with
an atomic mass of 29.97379 amu. What is the
atomic weight of silicon?
(A) 28.0856
(B) 28.1088
(C) 28.8342
(D) 29.0012
Sol.
Sol.
49.
45.
If isotopic distribution of C 12 and C14 is 98.0%
and 2.0% respectively, then the number of C 14
atoms in 12 gm of carbon is
(A) 1.032 Ã10 22
(B) 1.20 Ã10 22
(C) 5.88 Ã10 23
(D) 6.02 Ã10 23
The average atomi c mass of a m ixture
containing 79 mol % of 24 Mg and remaining
21 mole % of 25 Mg and 26Mg, is 24.31. %
mole of 26 Mg is
(A) 5
(B) 20
(C) 10
(D) 15
Sol.
Sol.
50.
46.
At one time there was a chemical atomic weight
scale based on the assignment of the value
16.0000 to naturally occurring oxygen. What
would have been the atomic weight, on such
a table, of silver, if current information had
been available? The atomic weights of oxygen
and silver on the present table are 15.9994
and 107.868.
(A) 107.908
(B) 107.864
(C) 107.868
(D) 107.872
The oxide of a metal contains 30% oxygen by
weight. If the atomic ratio of metal and oxygen
is 2 : 3, determine the atomic weight of metal.
(A) 12
(B) 56
(C) 27
(D) 52
Sol.
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```
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