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