Relative Molecular Mass

Chemistry Topic 3 Recap

Multiple Choice

Each element is defined by its

• Electron number

• Isotopes number

• Neutron number

• Proton number (atomic number)

Multiple Choice

The relative atomic mass is the average mass of an atom compared to 

• the mass of a carbon-12 atom.
• 1/12 the mass of a carbon-12 atom
• the mass of a hydrogen atom
• 1/12 the mass of a hydrogen atom

Multiple Choice

What is the atomic mass of magnesium?

• 2

• 4

• 12

• 24

Multiple Choice

What is the relative atomic mass (A_r) of Carbon?

• 6

• 12

• 18

• 7

Multiple Choice

What is the relative atomic mass (A_r) of Chlorine (Cl)?

• 35.5

• 17

• 18.5

• 0.5

Multiple Choice

What is the relative atomic mass (A_r) of Xenon (Xe)?

• 54

• 77

• 131

• 132

Fill in the Blanks

Which element has a relative atomic mass of 14?

CO₂

The little number next to the element tells us the number of atoms.

If there is no number this means there is 1 atom of that element.

How many atoms of Oxygen (O) are there in CO₂?

How many atoms of Carbon (C) are there in CO₂?

Multiple Select

In Sulfur hexafluoride (SF₆), how many atoms of Sulfur are there?

• 1

• 2

• 3

• 6

Multiple Select

In Sulfur hexafluoride (SF₆), how many atoms of Fluorine are there?

• 1

• 2

• 3

• 6

Multiple Choice

The relative molecular mass of a compound is equal to the sum of all its atoms'...

• Atomic masses

• Atomic numbers

• Oxidation numbers

• Outer shell electrons

Multiple Choice

Fluorine, F has a relative atomic mass (Ar) of 19. What is the relative molecular mass (Mr) of fluorine gas, F₂?

• 19

• 38

• 9

• 18

Multiple Choice

What is the relative molecular mass (M_r) of Hydrochloric Acid (HCl)?

Ar of H = 1, Ar of Cl = 35.5

• 18

• 34.5

• 36.5

• 35.1

To calculate Formula Mass

• Find the relative atomic mass of each element

• Count up how many atoms of each element and multiply this by the relative atomic mass of each one.

• Add up the total numbers

Fill in the Blanks

What is the relative formula mass of CH₄?

Relative atomic mass (Ar) of C = 12 , Ar of H = 1

1) Count up the Carbon (C) and Hydrogen (H) atoms in CH₄.

2) Next we can multiply the number of atoms by the relative atomic mass (Ar) of each element

So: Relative Formula mass (Mr) = ( _ x 12) + (4 x 1)

What number goes in the blank space?

Fill in the Blanks

What is the relative formula mass of CH₄?

Ar of C= 12, Ar of H = 1

Relative Formula mass (Mr) = (1 x 12) + (4 x 1)

What do you get when you do this calculation?

Multiple Choice

What is the relative formula mass of carbon monoxide (CO)

Ar of C = 12 , Ar of O = 16

(No little number means one atom of Carbon and one atom of oxygen per molecule.)

Formula mass = (1 x 12) + (1 x 16) = ....

• 24

• 28

• 30

• 44

Multiple Choice

What is the relative formula mass of Sodium Hydroxide NaOH?

Ar of Na = 23, Ar of H =1 , Ar of O = 16

Relative Formula Mass = (1 x 23) + (1 x 16) + (1 x 1) = ...

This give us...?

• 20

• 39

• 40

• 45

Fill in the Blanks

Calculate the relative formula mass of

Carbon Dioxide, CO₂

Ar of O = 16 ; C = 12

Relative Formula mass = (1 x 12) + ( _ x 16)

What is the missing number?

Fill in the Blanks

Calculate the relative formula mass of Carbon Dioxide, CO₂

Ar of O = 16 ; C = 12

Relative Formula mass = (1 x 12) + ( 2 x 16)

What does this give you in total?

Fill in the Blanks

Calculate the relative formula mass of Ammonia, NH₃?

Ar of N = 14 ; H = 1

-> Relative Formula mass = (1 x 14) + (3 x _ ) =

What is the missing number?

Fill in the Blanks

Calculate the relative formula mass of Ammonia, NH₃?

Ar of N = 14 ; H = 1

-> Relative Formula mass = (1 x 14) + (3 x 1) =

What is the answer for the relative formula mass then?

Fill in the Blanks

Calculate the relative formula mass of Sodium Chloride, NaCl?

Ar of Na = 23 ; Cl = 35.5

-> Relative Formula mass = ...?

Fill in the Blanks

Calculate the relative formula mass of Magnesium Bromide, MgBr₂?

Ar of Mg = 40, Ar of Br = 80

-> Relative Formula mass = ...?

Fill in the Blanks

Calculate the relative formula mass of Lithium Oxide, (Li₂O)

Ar of Li = 7, Ar of O = 16

-> Relative Formula mass = ...?

Fill in the Blanks

Calculate the relative formula mass of Sodium Sulfide, (Na₂S)

Ar of Na = 23, Ar of S = 32

-> Relative Formula mass = ...?

Fill in the Blanks

Calculate the relative formula mass of Potassium Sulfide, (K₂S)

Ar of K = 39, Ar of S = 32

-> Relative Formula mass = ...?

Fill in the Blanks

Calculate the relative formula mass of Calcium Carbonate (CaCO₃)

Ar of Ca = 40 , Ar of C = 12, Ar of O = 16

-> Relative Formula mass = ...?

Fill in the Blanks

Calculate the relative formula mass of Lithium Carbonate (Li₂CO₃)

Ar of Li = 7 , Ar of C = 12, Ar of O = 16

-> Relative Formula mass = ...?

Fill in the Blanks

Calculate the relative formula mass of Magnesium Hydroxide, Mg(OH)₂

You must multiply the total mass of a bracket by the little number around it!!

Ar of Mg = 24, O=16, H=1

-> Relative Formula mass = ...?

Fill in the Blanks

Calculate the relative formula mass of Rubidium Hydroxide, RbOH

Ar of Rb = 85, O=16, H=1

-> Relative Formula mass = ...?

Fill in the Blanks

Calculate the relative formula mass of Strontium Hydroxide, Sr(OH)₂

Ar of Sr = 137, O=16, H=1

-> Relative Formula mass = ...?

Multiple Choice

The formula of a compound is XO₂. Given that the M_r of the compound is 60, calculate the A_r of X.

Ar of O = 16.

• 32

• 28

• 92

• 94