Moles Calculations

Question 1

What is the mass number?

Answer 1

Total number of protons and neutrons in an atom

Question 2

What are isotopes?

Answer 2

Atoms of the same element that have the same number of protons but different numbers of neutrons

Question 3

What is the relative atomic mass?

Answer 3

The average mass of isotopes of an element compared to the mass of a Carbon-12 atom

Question 4

How to work out RAM

Answer 4

²⁴Mg = 77.6%
²⁵Mg = 10.1%
²⁶Mg = 11.3%
(24 x 78.6) + (25 x 10.1) + (26 x 11.3) / 100

Question 5

How do you calculate relative formula mass?

Answer 5

NH₃ = N + (Hx3) = 14 + 3 = 17

Question 6

How to calculate percentage abundance

Answer 6

total mass of element in compound / RFM of compound x 100

Question 7

How to calculate mole calculations using relative atomic mass and relative formula mass

Answer 7

mass = number of moles x RFM

Question 8

If the molecular formula is H₂O₂, what is the empirical formula?

Answer 8

HO

Question 9

How to work out the empirical formula from the mass of each element in a compound

Answer 9

• Determine the mass or percentage of elements.
• Divide the given mass or percentage by their RAM.
• Calculate the ratio of the atoms by dividing by smallest value.
Ca Br
20 80
20/40 80/80
0.5 1
0.5/0.5 1/0.5
1 : 2
CaBr₂

Question 10

How to work out volume with moles

Answer 10

• volume = moles x 24(dm³)

* volume = moles x 24000(cm³)

Question 11

What is the atomic number?

Answer 11

The number of protons in an atom