Stoichiometry Chemistry Worksheets With Answers Page 9
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1
2
3
4
5
6
7
8
9
10
11(D)
44 g
(E)
88 g
\
Explanations
1.
A
The formula for hydrogen sulfide is H
S; this means that its molar mass is equal to 2(1) + 32 = 34 g/mol. The closest answer
2
choice, and the correct answer, is A, which is thus slightly more than 1 mole. Don’t try to use the standard molar volume for
a gas in this problem, even though the problem asks about a gas, because the volume of the gas is not mentioned at all.
2.
C
This is a simple question: round the atomic masses that you get from the periodic table to calculate the molar mass of
C
H
OH. The answer is 2(12) + 6(1) + 16, which is equal to slightly more than 46 g/mol.
2
5
3.
A
Because there are two starting amounts, you might have guessed that one of them would act as a limiting reagent. The
reaction is written below, and you’ll need to start by finding all the molar masses to make your determinations. Round off the
numbers. The number of moles of nitrogen is 14 g (1 mol/28 g/mol) = 0.5 mol, and hydrogen = 15 g (1 mol/2 g/mol) = 7.5
mol. Now check to see which of the reactants is the limiting reagent. If you started with 0.5 mole of N
, in order to consume
2
this amount of nitrogen completely, you’d need to use 3(0.5) = 1.5 moles of hydrogen. You have much more hydrogen than
that (you have 7.5 moles), so nitrogen is the limiting reagent. The question asks you how much ammonia would be
produced, so now you know which reactant amount to use to calculate that, and the answer is 2(0.5 mol) = 1.0 moles, which
is equal to 17 g of NH
, answer choice A.
3
Molar
28
2
17
masses
N
+
2NH
Reaction
2
3
3H
2
No. of moles
0.5 mol available limiting
1.5 mol used 6.0 moles excess! 7.5 mol
1.0 mole produced
reactant
available
14 g
15 g
Slightly more than
Amounts
17 g
4.
D
This question gives you the grams of water but asks for atoms of hydrogen. You’ll need to find the number of water
molecules and then double it since H
O contains 2 atoms of H for every 1 molecule of water. The molar mass of water is
2
23
2(1) + 16 = 18 g/mol. The number of moles of water, then, is 12 g H
O (1 mol/18 g/mol) = .66 mol of 6 (as in 6.02
10
)
2
23
23
is 4
10
molecules of water. Doubling that you get 8
10
hydrogen atoms.
5.
B
This question is a percent composition question, so you’ll be looking for the molecule that has the largest mass of H
compared to its whole molar mass. Examine the analysis below, and it’s clear that water has the highest percent
composition of hydrogen.
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