1. Lead can form multiple compounds with oxygen as shown below:
Pb
O
Compound A 2.98 g 0.461 g
Compound B 9.89 g 0.763 g
a. Determine the ratio of oxygen to lead in each of the compounds.
0.461 g O
2.98 g Pb
= 0.1546979866
0.763 g O
9.89 g Pb
= 0.077149635
b. If the chemical formula for compound B is PbO2, what is the possible formula for compound A?
SHOW ALL WORK.
Because the ratio of Cmpd A is different from Cmpd B, we know they are 2 different chemicals (LODP). To find
the relationships between the two, we must use the LOMP.
To do this, divide both ratios by the smallest value:
0.1546979866
0.077149635
= 2.005194086 = 2
0.077149635
=1
0.077149635
Cmpd A has two times as much oxygen as Cmpd B. If Cmpd B is PbO2, then Cmpd A must be PbO4
c. You find a sample of 8.45 g sample of lead compound. It is analyzed to contain 0.652 g of lead. Is it
a sample of compound A, compound B, or neither? Explain.
To determine the identity of this third sample, we must find its definite proportion and then compare this ratio
to the ones calculated in #1a. If this value matches either of them, then we know whether it is A, B, or neither.
8.45 g of compound must equal the sum of the elemental masses, thus a total of 8.45 grams of the elements.
(LOCOM). If there is 8.45 grams of the cmpd and 0.652 g of lead, then there must be 7.798 g of oxygen.
8.45 g of Pb and O
-0.652 g Pb
7.798 g O
The definite proportion is
7.798 g O
0.652 g Pb
This is a new compound of lead oxide.
= 11.9601227 = 12
2. Complete the table and describe the relationship between the two iron oxide compounds:
Sample
I
II
Total Mass
(g)
75.00
56.00
Mass Fe
(g)
52.46
43.53
Mass O
(g)
22.54
12.47
Mass ratio (O to Fe)
0.4296606939
0.2864691018
Are the two samples from the same compound or different compounds? Explain.
Different - their definite proportions are different. According to the LODP, every chemical has a defined ratio
between the masses of the elements. This ratio cannot change in a pure compound.
Derive formulae for the samples.
To do this, divide both ratios by the smallest value:
0.4296606939
0.2864691018
0.2864691018
=1
0.2864691018
= 1.499850041 = 1.5
Because these ratios must be integers, multiply both products by 2 to keep the ratio the same but using whole
numbers.
0.4296606939
0.2864691018
= 1.499850041 = 1.5 x2 = 3
0.2864691018
0.2864691018
=1x2=2
Sample I has a ratio of three to two in terms of the number of oxygen when compared to Sample II.
The simplest formulas for both compounds would be:
Sample I
Sample II
FeO3
FeO2