Molecular And Empirical Formula (OG)

Question 1

Define Molecular Formula

Answer 1

The molecular formula of a compound is the actual number of atoms of the element in that compound

Question 2

When writing the molecular formula of an organic compound…

Answer 2

We first must draw the carbon atoms then the hydrogen atoms then any other atoms are listed alphabetically.

Question 3

Define the Empirical formula

Answer 3

The empirical formula is the simplest whole number ratio of the atoms of each element in a compound

Question 4

How would you calculate the empirical formula?

Answer 4

Divide all numbers in the molecule by the smallest number present if the number is a decimal e.g. 2.5 then multiple all numbers by 2 to get a whole number

Question 5

Example question: A sample of a hydrocarbon contained 0.48g of carbon and 0.08g of hydrogen. Calculate the empirical formula.
Ar C=12.0, Ar H=1.0

Answer 5

1: Find the moles of carbon and hydrogen (n=m/mr)
2:Then divide both numbers by the smallest number to determine the ratio
Example:
1: carbon- 0.48/12.0=0.04mol and Hydrogen- 0.08/1.0=0.08mol
2: divide both by 0.04 carbon=1 and hydrogen=2

Answer=CH2

Question 6

Calculate the molecular formula from the empirical formula example:
Relative molecular mass of compound aka Mr=(28.0g/mol)
Empirical formula=CH2—>14.0g/mol

Answer 6

1:Mr of compound/Mr of empirical formula
E.g. 28.0/14.0=2.0
2: Multiple the empirical formula by the answer to get the molecular formula
E.g. CH2x2 is C2H4 aka ethene