Level Chemistry Transition Unit Worksheet With Answer Key - Healthcote School Page 11
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1710
Yields and atom economy
Task 9:
mass of product obtained
% yield =
× 100
maximum theoretical mass of product
M
wanted
product
from
equation
r
Atom economy =
× 100
total
M
of
products
from
equation
r
1 Quicklime (calcium oxide, CaO) can be made by thermal decomposition of limestone (calcium
carbonate, CaCO
). CaCO
CaO + CO
3
3
2
a Calculate the maximum theoretical mass of quicklime that can be made by heating 50 g of
limestone (relative atomic masses: C = 12, O = 16, Ca = 40).
28 g
b In the reaction, only 26 g of quicklime was produced. Calculate the percentage yield.
92.9%
2 Aluminium is made by the electrolysis of aluminium oxide. Calculate the atom economy for the
production of aluminium in this reaction. (relative atomic masses: O = 16, Al = 27)
2 Al
O
→ 4 Al + 3 O
2
3
2
52.9%
3 Hydrazine (N
H
) was used as the rocket fuel for the Apollo missions to the moon. It is made by the
2
4
reaction of ammonia (NH
) with sodium chlorate (NaOCl) (relative atomic masses: H = 1, N = 14, O
3
= 16, Na = 23, Cl = 35.5).
ammonia
+ sodium chlorate
→ hydrazine
+
sodium chloride
+
water
2 NH
+
NaOCl
→
N
H
+
NaCl
+
H
O
3
2
4
2
a Calculate the maximum theoretical mass of hydrazine that can be made by reacting 340 g of
ammonia with an excess of sodium chlorate.
320 g
b In the reaction, only 280 g of hydrazine was produced. Calculate the percentage yield.
87.5%
c Give three reasons why less than the maximum theoretical yield was produced.
Reaction’s reversible, some NH
lost separating it from the reaction mixture, other reactions take place
3
.
d Calculate the atom economy for this way of making hydrazine.
29.5%
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