F321: Calculations

Question 0

Relative isotopic mass

Answer 0

The mass of an atom of an isotope compared to 1/12th the mass of carbon-12. (on a scale where 12 is exactly 12)

Question 1

Isotope

Answer 1

Atoms with the same number of protons but a different number of neutrons (same e- arrangements so same chemical properties)

Question 2

Relative atomic mass

Answer 2

Average mass if an atom of an element compared to 1/12th the mass of carbon-12

Question 3

Calculating Ar

Answer 3

From the mass and relative abundance of all the isotopes
Eg. for 75% 35Cl and 25% 37 Cl
(75x35)+(25x37)/100 = 35.5

Question 4

Calculating Mr and RFM

Answer 4

Add up individual relative atomic masses

Question 5

Mole

Answer 5

The amount of a substance which contains as many particles as there are atoms in 12g of Carbon-12

Question 6

Avogadro’s constant

Answer 6

The number of particles in one mole of a substance’ 6.02x10^23

Question 7

Working out empirical formula

Answer 7

Divide masses (or %) by Ar to work out ratio of moles, divide all by the smallest number to give a whole number ratio
(Look out for halves- double values if so)

Question 8

Working out the molecular formula

Answer 8

Compare Mr of empirical formula with the Mr given for the molecule. Multiply by a certain factor to make them the same.

Question 9

Concentration

Answer 9

A measure of the number of moles of a solute dissolved per dm3 of solvent

Question 10

Stoichiometry

Answer 10

Molar ratios