Molecular Formula

Question 1

What is a MOLECULAR formula?

Answer 1

Determines the ACTUAL NUMBER of elements in a compound.

Question 2

What are the FOUR STEPS in getting the molecular formula in a compound?

Answer 2

1. Empirical Formula
2. Empirical Molar Weight
3. Molar Weight Ratio
4. Molecular Formula

Empi Formula -> Empi Molar W. -> Molar W. Ratio -> Molec Formula

n= MW molecular formula
———————————
MW empirical formula

Molecular Formula= n(Empirical Formula)

Question 3

What is the n in the formula?

Answer 3

integer multiple of the EF subscripts

Question 4

If the problem already has a given EMPIRICAL FORMULA (compound na), how to get the MOLECULAR FORMULA?

Answer 4

PROCEED TO GET THE EMPIRICAL MOLAR WEIGHT. (STEP 2)
how?

get the moles from the empi formula of an element, then multiply to its corresponding atomic weight.

unit: g/mol

DO STEPS 3 AND 4 NEXT

Question 5

Explain STEP 3 AND 4.

Answer 5

Step 3: get the molar weight ratio.

Question 6

If the problem already DOES NOT have a given Empirical Formula but only has a PERCENTAGE OF THAT ELEMENT, what to do?

Answer 6

Get the empirical formula first.
(dividing it to the atomic weight, subscripts & divide to the lowest, multiply if needed)

PROCEED TO STEPS 2,3, AND 4.

Question 7

If the problem already DOES NOT have a given Empirical Formula but only has a PERCENTAGE OF THAT ELEMENT, what to do?

Answer 7

Get the empirical formula first.
(dividing it to the atomic weight, subscripts & divide to the lowest, multiply if needed)

PROCEED TO STEPS 2,3, AND 4.