Homework Solutions

3:29
a.    = 1.66 x 10-22 mole

100 molecules
6.022 x 1023 molecules/mole

b.    = 5.55 mole
 

100.0 g H2O
18.016 g/mole

c.    = 8.30 x 10-22 mole

500 atoms of Fe
6.022 x 1023 atoms/mole

d.    = 8.95 mole

500.0 g Fe
55.85 g/mole

e.    = 2.49 x 10-22 mole

150 molecules of N2
6.022 x 1023 molecules/mole

f.    = 0.939 mole

150 g Fe2O3
[2(55.85 g/mole)+3(16.00 g/mole)]

g.    = 2.17 x 10-4 mole

10.0 mg NO2 1 g
(14.01 g/mole) + 2(16.00 g/mole) 1000 mg

3:32
a.    14(12.01 g/mole) + 18(1.008 g/mole) + 2(14.01 g/mole) + 5(16.00 g/mole) = 294.304 g/mole = 294.30 g/mole
b.    =1.6989 x 10-4 moles = 1.7 x 10-4 moles

0.050 g Aspartame
294.30 g/mole

c.    1.56 moles * 294.30 g/mole = 459.108 g = 459. g
d.    5.0 mg --> 1.7 x 10-4 moles (see b) * 6.022 x 1023 molecules/mole = 1.0 x 1020 molecules
e.    = 4.9 x 1022 atoms N

1.2 g Aspartame 2 moles N 6.022 x 1023 atoms N
294.30 g/mole 1 mole Aspartame 1 mole N

f.= 4.89 X 10-13 g

294.30 g/mole 1.00 x 109 molecules
6.022 x 1023 molecules/mole  

g.    = 4.89 x 10-22 g

294.30 g/mole
6.022 x 1023 molecules/mole

3:13    The empirical formula reveals the relative number of each atom, these numbers presented in the lowest whole-number ratio.  The molecular formula reveals the actual number of each atom in the molecule.  If the actual number of each atom is such that there is one atom of one of the elements of the molecule, then the actual number of each atom is in the lowest whole-number ratio and the empirical formula and the molecular formula are the same.

3:44   
56.79 g C / (12.01 g/mole) = 4.72856 moles --> 8 moles
6.56 g H / (1.008 g/mole)   = 6.5079 moles   --> 11 moles
28.37 g O / (16.00 g/mole) = 1.7731  moles  --> 3 moles
8.28 g N / (14.01 g/mole)   = 0.59101 moles --> 1 mole        

(divide the numbers in the second column by 0.59101-the smallest of them-to get the numbers in the third column)

C8H11O3N

3:47
49.31 g C / (12.01 g/mole)  =  4.1057 moles  --> 1.5  --> 3 moles
43.79 g O / (16.00 g/mole)  =  2.7369 moles  --> 1.0  --> 2 moles
6.90 g H / (1.008 g/mole)    =  6.8452 moles  --> 2.5  --> 5 moles

(the numbers in the third column are not whole numbers.  Multiply by '2' to make them all whole.)

empirical formula:  C3H5O2 which has a formula weight of 73.07 g/mole.  Because the actual molecular weight is 146.1 g/mole
the molecular formula must be C6H10O4.

3:36
a.    96.08/194.2 = 49.47 % C
b.    144.12/342.296 = 42.1 % C
c.    24.02/46.068 = 52.1 % C
c>a>b

3:37
a.    14.01/26.02 = 53.84 % N
b.    14.01/42.02 = 30.45 % N
c.    28.02/84.04 = 30.45 % N
d.    28.02/44.02 = 63.65 % N