Unit 6 - Chemical Formulas

Question 1

What are the three types of Chemical Formulas?

Answer 1

1. Empirical Formula
2. Molecular Formula
3. Structural Formula

Question 2

Definition of Empirical Formula (3)

Answer 2

1. Simplest Ratio of Atoms
2. All Ionic Compounds Formulas are Empirical
3. Covalent Formula can be Empirical too

Question 3

Why are all ionic compound formulas empirical?

Answer 3

They do not form a discrete molecule, but rather a crystal lattice, so there’s no point in have unsimplified ratios

Question 4

Definition of Structural Formula (2)

Answer 4

1. Provides info on HOW elements are bonded
2. Only useful for covalent compounds

Question 4

Definition of Molecular Formula

Answer 4

1. Actual number of atoms per element
2. May be multiple of the empirical formula
3. May be the same as the empirical formula

Question 5

Definition of Molecular Weight

Answer 5

Sum of masses of atoms in the molecule

Question 6

What is “u” short for?

Answer 6

Atomic Mass Units

Question 7

How do you find the molecular formula when given percent compositions? (5)

Answer 7

1. Find Empirical Formula
2. Find Molecular Weight of E. Form.
3. Molecular Weight/Given Molar Mass
4. Round Quotient (nearest ones place)
5. Multiply all subscripts by quotient

Question 7

How do you determine the Empirical Formula when given percent compositions? (5)

Answer 7

1. Change all % to grams (Ex: 22.1% to 22.1 g)
2. Identify atomic mass of elements in PT (Ex: Al - 27)
3. Divide grams by the molar mass (Ex: 22.1/27 = 0.82)
4. Divide the quotients of each element by the smallest quotient (Ex: 3.3/0.82 & 0.82/0.82)
5. A Ratio is Formed (if a decimal, take smallest multiple) (Ex: 1:1.5 = 2:3)

Ex:

Element - Percent to Gram - Molar Mass - Quotient - Ratio
Al - 22.1 - 27 - 0.82 - 1
P - 25.4 - 31 - 0.82 - 1
O - 52.5 - 16 - 3.3 - 4
AlPO4