4. Formula Writing

Question 1

How do you find the formula of methane?

Answer 1

Covalent
Swap over method

4 1
C H
1 : 4
= CH4

Question 2

How do you find the formula of Strontium Chloride?

Answer 2

Ionic
Swap over method with charges

2+ 1-
Sr Cl
1 : 2

= Sr2+ (Cl-)2

Question 3

How do you find the formula of Copper (II) Chloride?

Answer 3

Transition Metal Ionic
Swap over method with given charge

2+ 1-
Cu Cl
1 : 2

= Cu2+ (Cl-)2

Question 4

How do you find the formula of Magnesium Nitrate?

Answer 4

Group Ionic
Swap over with group formula found in Data Booklet

2+ 1-
Mg NO3
1 : 2

= Mg2+ (NO3-)2

Question 5

What are the formula prefixes?

Answer 5

Prefixes
Don’t do swap over

Mono = 1
Di = 2
Tri = 3
Tetra = 4
Penta = 5
Hexa = 6
Hepta = 7
Octo = 8

Question 6

Balance this equation:

Combustion of Methane

CH4 + O2 —————> CO2 + H2O

Answer 6

Balancing Chemical Equations

 C = 1                                   C = 1
 H = 4                                  H = 2>4
 O = 2>4                             O = 3>4

= CH4 + 2 O2 —————> CO2 + 2 H2O

Question 7

How do you find the GFM of Calcium Carbonate?

Answer 7

Add up all RAMs (in Data Booklet)

Ca CO3
= 40 + 12 + (3x16)
= 100amu

Question 8

Find the number of moles in 54g or H2O

Answer 8

Use n = m
GFM

n = 54
(2x1) + 16
= 3 moles

Question 9

Find the mass of CO2 if the mass of CH4 is 4g in this equation:

CH4 + 2 O2 —————> CO2 + 2 H2O

Answer 9

What you do to the first side, you do to the other

/ *
CH4 + 2 O2 —————> CO2 + 2 H2O
1 mole 1 mole

= 12 + (4x1) = 12 + (2x16)
= 16g = 44g
= 4g = 11g