Chemical Calculations

Question 1

What is relative atomic mass (Ar) and how do you find it?

Answer 1

It is the average mass of an atom of a specific element

(% of isotope x mass of isotope ) + (% of isotope x mass of isotope) / 100

Question 2

What is the relative formula mass (Mr) and how do you find it?

Answer 2

Mass of a molecule

(# of that element in the molecule x relative atomic mass) + (# of that element in the molecule x relative atomic mass)

Question 3

What is a mole?

Answer 3

A mole is a substance, like a dozen; you can have a mole of carbon.

Question 4

How is a mole used to represent the amount of a substance?

Answer 4

Having a mole of something is having 6.022 x 10²³ of it

Question 5

How is a mole the same as the Avogadro number of particles in a substance?

Answer 5

As if you have 1 mole of an element, its weight in grams will be its atomic mass

Question 6

Carry out mole calculations using relative atomic mass (Ar) and relative formula mass (Mr)

Answer 6

Number of Moles = Mass in g / Mr or Ar

E.g. Number of moles in 66g of carbon dioxide

Mr = 12 + 16 + 16 = 44

Number of Moles = 60 / 44 = 1.5 moles of carbon dioxide

Question 7

How much is a molar volume of gas and its values?

Answer 7

One mole of any mass will occupy 24,000 cm³; which is 24 dm³

Molar Volume (dm³) = Volume (dm³) / Moles

Answer always in dm³