Chapter 3.2 Determining the Formula of An Unknown Compound

Question 1

Empirical Formula

Answer 1

Shows the lowest whole number of moles, thus the relative number of atoms, of each element in the compound

Question 2

Example of Empirical Formula (What is the Empirical Formula of Hydrogen Peroxide?)

Answer 2

Hydrogen Peroxide = 1 part by mass of H for every 16 parts by mass of O
*So… there is 1 H atom for every 1 O atom which means that the empirical formula is HO

Question 3

Molecular Formula

Answer 3

shows the actual atoms of each element in a molecule

Question 4

Example of Molecular Formula (What is the Molecular Formula of Hydrogen Peroxide?)

Answer 4

the molecular formula is H2O2 (twice the empirical formula)

Question 5

Structural Formula

Answer 5

shows the relative placement and connections of atoms in the molecule

Question 6

Example of Structural Formula (what is the structural formula of hydrogen peroxide?)

Answer 6

H-O-O-H

Question 7

How to find the Empirical Formula (3 steps)

Answer 7

1. Find the mass of each component element
2. Convert each mass to Mole, and write out the new formula
3. convert the amounts (in moles) mathematically to whole number subscripts by DIVIDING each subscript by the SMALLEST subscript
   * if necessary, multiply through by the smallest whole number that turns all subscripts into whole numbers

Question 8

How to find molecular formula

Answer 8

*use empirical formula + molar mass of compound:

Whole number multiple = (molar mass g/mol) / (empirical formula mass g/mol)

Question 9

Example of HOW TO FIND molecular formula (what is the molecular formula of Hydrogen Peroxide?)

Answer 9

HO molar mass = 30.02 g/mol / HO Empirical formula mass (17.01), SO
MM = 30.02/17.01 = 2
*multiplying the empirical formula (HO) by 2 = molecular formula = H(1x2)O(1x2) = H2O2

Question 10

How to find Formula from Mass Percent (equation)

Answer 10

1. Assume there is 100.0 g of compound to express each mass percent directly as mass in grams
2. Convert each mass (g) to amount in moles
3. Derive the empirical formula
4. Follow the steps for molecular formula to find the whole-number multiple and the molecular formula

Question 11

Combustion analysis

Answer 11

used to measure the amounts of carbon and hydrogen in a combustible organic compound

Question 12

How to find the mass in a combustion analysis question

Answer 12

mass = subtracting the masses of Carbon and Hydrogen from the original mass of the compound

Question 13

Isomers

Answer 13

two or more compounds with the same molecular formula

Question 14

Structural isomerism

Answer 14

(simplest type of isomerism) occurs when atoms link together in different arrangements