Chemical Calculations (Part 1)

Question 1

Relative Atomic Mass

Answer 1

The average mass of an atom of an element relative to 1/12th of the mass of one atom of carbon-12

Question 2

Relative Formula Mass

Answer 2

Average mass of a molecule relative to 1/12th of the mass of one atom of carbon-12. The sum of all the relative atomic masses of all atoms present in its formula

Question 3

Isotopes

Answer 3

Atoms of the same element with the same number of protons but different number of neutrons

Question 4

Relative Isotopic Mass

Answer 4

Mass of an isotope of an element compared to 1/12th of the mass of one atom of carbon-12

Question 5

Ar equation

Answer 5

The sum of (relative isotopic mass x relative abundance for each isotope) divided by 100

Question 6

What does the mass spectroscopy identify?

Answer 6

The number and amount of each isotope present in a sample of an element

Question 7

Mass Spectroscopy Steps

Answer 7

Ionisation - An electron gun bombards sample with a beam of high energy electrons and ionises atoms/molecules forming positive ions
Acceleration - The positive ions are accelerated by the negatively charged electric plates
Deflection - The ions are then deflected by a magnetic field according to their masses and charges
Detection - Ions with the correct mass/charge ratio pass through and are detected. Current in the electromagnet is varied so different mass ions hit the detector.
Number of peaks = number of isotopes present in sample

Question 8

Mass spectrum of chlorine

Answer 8

Atoms - Cl35 = 75%
Cl37= 25%
Molecules - (35-35) = mass 70, ratio 9
(35-37)= Mass 72, Ratio 6
(37-37) = Mass 74, ratio 1

Question 9

A Mole

Answer 9

The amount of any substance containing as many particles as there are carbon atoms in exactly 12g of the carbon-12 isotope

Question 10

The Avagadro Constant

Answer 10

Na is the number of atoms per mole of the carbon-12 isotope

Question 11

How do you work out the mass, Mr or moles ?

Answer 11

Mass = Mr x Moles

Question 12

Molecular Formula

Answer 12

The actual number of atoms of each element present in the molecule

Question 13

Empirical Formula

Answer 13

The simplest whole number ratio of the atoms of each element in a compound

Question 14

Name all diatomic molecules

Answer 14

Hydrogen
Oxygen
Nitrogen
Chlorine
Flourine
Bromine
Iodine

Question 15

How do you find the molecular formula ?

Answer 15

Actual Mr ( molecular) / Mr ( Empirical )

Question 16

How do you find the number of particles ?

Answer 16

Na x number of moles