Transcript Challenge Questions - Empirical and Molecular Formula

Practice: Empirical and Molecular Formula
1. For a group of 2 or 3
2. Collect pens and a whiteboard!
3. Prepare yourself!
Q1 EASY
A compound contains 65.66 % carbon, 15.19 % hydrogen by
mass and the rest nitrogen. Calculate the compound's empirical
formula.
1 mol
15.0396 mol
mol H = 15.19 g x
= 15.0396 mol ;
» 11
1.01 g
1.3669 mol
1 mol
5.46711 mol
mol C = 65.66g x
= 5.46711 mol ;
»4
12.01g
1.3669 mol
1 mol
1.3669 mol
mol N = 19.15g x
= 1.3669 mol ;
»1
14.01g
1.3669 mol
Emp. Formula = C4 H 11 N
Q2 MODERATE
A small sample of antifreeze contains 4.51g C, 1.13 g H, and
6.01g O. The molar mass is 62.0 g/mol. Determine the empirical
formula and the molecular formula.
mol H = 1.13 g x
1 mol
1.11881 mol
= 1.11881 mol ;
»3
1.01 g
0.37552 mol
mol C = 4.51g x
1 mol
0.37552 mol
= 0.37552 mol ;
»1
12.01g
0.37552 mol
mol O = 6.01g x
1 mol
0.375625 mol
= 0.375625 mol ;
»1
16.00g
0.37552 mol
Emp. Formula = CH 3O
N=
Molecular Mass 62.0g / mol
=
=2
Empiracle Mass 31.04 g / mol
Molec Formula = C2 H 6O2
Q3 MODERATE/HARD
A compound is 81.7% carbon and 18.3% hydrogen.
a. What is its empirical formula?
b. The formula weight of this compound is 352.9 g/mol. What is the
molecular formula?
1 mol
18.188 mol
= 18.188 mol ;
» 2.67 ; 2.67x3 = 8
1.01 g
6.8027 mol
1 mol
6.8027 mol
mol C = 81.7g x
= 6.8027 mol ;
»1
;1 x 3 = 3
12.01g
6.8027 mol
C3 H 8
Molecular Mass 352.9 g / mol
N=
=
=8
Empiracle Mass 44.11 g / mol
C24 H 64
mol H = 18.3g x
Q4 HARD
Hemoglobin is the oxygen carrying compound found in human blood.
It is found to contain 0.3335% iron by mass. It is already known that
one molecule of hemoglobin contains four atoms of iron. What is the
molecular mass of hemoglobin?
One iron weighs 55.85 g / mol; four of them weigh 223.40 g / mol
This value ( 223.38 g / mol ) represents 0.3335% of the total mass of hemoglobin.
100%
223.38 g / mol x
= 66,980 g / mol
0.3335%
x = 66,980 g / mol
Q5 HARDEST!
Calculate the molar mass of a metal that forms an oxide having
the empirical formula M2O3 and contains 68.04% of the metal by
mass. Identify the metal.
68.04% of the compound is the metal, therefore 31.96% is oxygen.
The three oxygen's weigh 48.00 and this represents 31.96% of the total weight.
100%
= 150.19g / mol Molar Mass!
31.96%
Subtract 48.00 g / mol from 150.19 g / mol to get 102.19 g / mol!
48.00 g / mol x
102.19 g / mol is the weight contribution of M 2 .
Dividing by two gets 51.10 g / mol.
The nearest atomic weight on the periodic table belongs to that vanadium!
Chemistry 11 – Class Starter
1. Hebden: p. 95 Q’s 52,54,55 (Challenge
Questions)
Finished…?
1. Hand the completed quiz at the front of the
room
2. Collect the Lab: Dehydration of a Hydrate
3. Read the introduction, and use the handout
to create your Pre-Lab which is due at the
BEGINNING of next class