Arsenic is often obtained by heating the ore
arsenopyrite, FeAsS. The decomposition of FeAsS is
represented by the balanced equation below.
FeAsS(s) ==heat==>FeS(s) + As(g)
In the solid phase, arsenic occurs in two forms.
One form, yellow arsenic, has a density of 1.97 g/cm3
at STP. The other form, gray arsenic, has a density of
5.78 g/cm3
at STP. When arsenic is heated rapidly in air, arsenic(III)
oxide is formed. Although arsenic is toxic, it is needed by the
human body in very small amounts. The body of a healthy human
adult contains approximately 5 milligrams of arsenic.
79 Convert the mass of arsenic found in the body
of a healthy human adult to grams. [1]
HIGHLIGHT TO SEE THE ANSWER
|
(5mg
use Table C, Take out the m and put in x10-3)
ANSWER==>
5x10-3
g
or
0.005 g. |
80 When heated, a 125.0-kilogram sample of
arsenopyrite yields 67.5 kilograms of FeS. Determine the
total mass of arsenic produced in this reaction. [1]
HIGHLIGHT TO SEE THE ANSWER
|
Find the missing mass
125.0kg-67.5kg=57.5kg |
81 Write the formula for the compound
produced when arsenic is heated rapidly in air. [1]
HIGHLIGHT TO SEE THE ANSWER
|
As2O3
(Arsenic(III) oxide) |
82 Explain, in terms of the arrangement of
atoms, why the two forms of arsenic have different densities
at STP. [1]
HIGHLIGHT TO SEE THE ANSWER
|
In gray
arsenic, the atoms are arranged closer together
so there is more mass in a unit volume.
The
atoms in yellow As are farther apart; therefore,
there is less mass per volume than in gray As. |
83 Calculate the percent composition by mass
of arsenic in arsenopyrite. Your response must include
both
a correct numerical setup and the calculated result.
[2]
LINK TO SEE THE ANSWER