Empirical Formula
p.229
simplest whole number ratio for a formula
Steps for determining empirical formula.
1. mass of each element converted to moles.
2. divide each mole number by smallest number.
Ws.9.3
1. Cholesterol: 83.39%Carbon, 11.99%Hydrogen, 4.14%Oxygen
“When given % assume 100 gram sample”
C27H46O
2. Freon: 9.9%Carbon, 58.64%Chlorine, 31.43%Fluorine
CCl2F2
3. 10.1%carbon – 0.9%hydrogen – 89.1%chlorine
4. 11.19% hydrogen – 88.81%oxygen
5. 26.5%potassium – 35.4%chromium – 38.1%oxygen
6. 5.91g magnesium – 17.18g chlorine
7. 4.29g carbon – 5.71g oxygen
8. 8.270 g iron – 3.17g oxygen
9. Aspirin: 60.85%C – 4.38%H – 34.75%O
AP problem p. 125
The compound Adrenaline contains 56.79% C,
6.56% H, 28.37%O and 8.28%N by mass.
What is the empirical formula for adrenaline?
Molecular Formula
p.232
Empirical formula is simplest whole # ratio
Molecular formula is “real world” whole# ratio
X =
molecular formula mass
empirical formula mass
X (empirical Formula) = molecular formula
X is a whole # multiple
**clue**Molecular formula mass is usually given by experiment in problem.
X = molecular mass / empirical mass
x (empirical mass) = molecular formula
Ws.7.4
1. CHO: experimental molar mass 116.07
C4H4O4
2. C2H4O: experimental molar mass 88
C4H8O2
3. C3H4O: experimental molar mass = 168.19
4. Caffeine is a stimulant found in many drinks.
Caffeine’s molar mass is 194.19g. The elemental
analysis is 96.08g Carbon, 10.08g Hydrogen, 56.04g
Nitrogen, 32.00g Oxygen. Calculate its molecular
formula.
5. The molar mass from experimentation = 392.2g.
The experiment also determined the sample to be 0.70g
Chromium, 0.65g Sulfur, and 1.30g Oxygen. Calculate
the molecular formula.
6. Propene has the simplest formula CH2. What is the
molecular formula if it has a molar mass of 42.90g/mol?
7. Histamine is a substance that is released by cells in
response to injury, infection, stings, which may cause
allergic responses. People sometime take antihistamine
drugs to counter act the effects of histamine. A sample
histamine is composted of 208mgC, 31mgH, and 146mgN.
The molar mass of this histamine is 111g/mol.
Calculate the molecular formula for this histamine.
AP problem:
Many homes in rural America are heated by
propane gas, a compound that contains only
carbon and hydrogen. Complete combustion of
a sample of propane produced 2.641g of
Carbon dioxide and1.442g of water as the only
products. Find the empirical formula.