50 g of ZnS are strongly heated in air to effect partial oxidation and the resultant mass weighed 44 g. What is the ratio of ZnO to ZnS in the resulting mixture?
Answers
Answer:
Explanation:
Explanation:
Start by taking a look at the balanced chemical equation that describes this reaction. Zinc sulfide will react with oxygen gas to produce zinc oxide and sulfur dioxide.
2
ZnS
(
s
)
+
3
O
2
(
g
)
→
2
ZnO
(
s
)
+
2
SO
2
(
g
)
Now, you know that your sample of zinc sulfide undergoes partial oxidation, which means that only a fraction of the mass of zinc sulfide will react to produce zinc oxide.
Notice that zinc sulfide and zinc oxide are present in a
1
:
1
mole ratio because it takes
2
moles of zinc sulfide to produce
2
moles of zinc oxide.
Use the molar masses of the two compounds to convert this mole ratio to a gram ratio.
You will have
1 mole ZnS
1 mole ZnO
=
1
mole ZnS
⋅
97.474 g
1
mole ZnS
1
mole ZnO
⋅
81.40 g
1
mole ZnO
=
97.474 g ZnS
81.40 g ZnO
So, you know that the reaction produces
81.40 g
of zinc oxide for every
97.474 g
of zinc sulfide that take part in the reaction.
This is equivalent to saying that when
1 g
of zinc sulfide is oxidized, the reaction produces
0.8351 g
of zinc oxide.
In other words, if the reaction consumes
1 g
of zinc sulfide, the total mass of the sample will decrease by
ZnS consumed
1 g
−
ZnO produced
0.8351 g
=
0.1649 g
In your case, the total mass of the sample decreases by
50 g
−
44 g
=
6 g
which means that the reaction must have consumed
6
g decrease
⋅
1 g ZnS
0.1649
g decrease
=
36.39 g
This implies that the resultant mixture contains
what you start with
50 g ZnS
−
what is consumed
36.39 g ZnS
=
what remains unconsumed
13.6 g ZnS
Consequently, the resultant mixture also contains
ZnS + ZnO
44 g
−
ZnS
13.6 g
=
ZnO
30.4 g
Therefore, you can say that the resulting mixture contains zinc oxide and zinc sulfide in a
30.4
:
13.6
gram ratio, which is pretty close to option (D).
The difference between the values was probably caused by the values I used for the molar masses of the two compounds.