1. Types of Chemical Formulas

2. Types of Chemical Formulas
Molecular
number of atoms present in the smallest particle of that compound
C6H12O6
Empirical
simplest whole number ratio of atoms in a compound
CH2O

3. just reduce or simplify the coefficients as you would a fraction.
To go from molecular C6H12O6 to empirical CH2O as seen on the last side…..
just reduce or simplify the coefficients as you would a fraction.
Keep in mind: the coefficients must be in the same ratio.
C6H12O6 all coefficients are divisible by 2.

4. Determine Empirical Formula from Mass Ratio of Elements
A compound consists of 24g C and 64g O
What is the empirical formula of the
compound?
Step 1
Change the masses to moles.
The number of moles of each element are your subscripts

5. 24g C ÷ 12g C = 2.0mol C
64g O ÷ 16g O = 4.0mol O
So make these your subscripts……
C 2.0 O 4.0

6. CO2 Step 2 subscripts must be smallest whole numbers
C 2.0 O 4.0 reduces to
CO2

7. Practice…what is the empirical formula?
A pure sample contains 14g N and 8g O
A compound consists of 36.0g C and 12.0g H
A substance consists of 52g Cr and 24g O
N2O
CH4
Cr2O3

8. Practice…what is the empirical formula?
A pure sample contains 14g N and 8g O
14g N ÷ 14g N = 1 mol N
8gO ÷ 16g O = 0.5 mol O
A compound consists of 36.0g C and 12.0g H
36g C ÷ 12g C = 3 mol C
12g H ÷ 1g H = 12 mol H
A substance consists of 52g Cr and 24g O
52g Cr ÷ 52g Cr = 1 mol Cr
24gO ÷16g O = 1.5 mol O
N2O
CH4
Cr2O3

9. Finding Molecular Formula from Empirical Formula
Empirical formula: CH3
If the molecular mass of the substance is 30g what is the molecular formula?
Step 1: make a list of possible molecular formulas
CH3, C2H6, C3H9, C4H12 …..

10. Step 2: Determine molar masses of your list of molecules.
Step 3: whichever matches is your answer
C2H6
2(C) x12 = 24g
+ 6(H) x 1 = 6g
30g

11. Practice
A 39g sample of a gaseous substance contains 18g C and 21g nitrogen
What is the empirical formula? CN
If the molecular mass = 52g what is the molecular formula?
C2N2

12. What is the empirical formula of a hydrocarbon that consists of 84g carbon and 14g hydrogen?
CH2
If its molar mass is 112g, what is its molecular formula?
C8H16

13. A compound known as a hydrate has the formula: K2CrO4∙ 6H2O
A compound known as a hydrate has the formula: K2CrO4∙ 6H2O. What percentage of this compound is water?
36%

14. The END