1.3 Chemical Calculations

Question 1

Relative Atomic Mass

Answer 1

Is the average mass of one atom of the element relative to one-twelfth the mass of one atom of carbon-12

Question 2

Relative Isotopic Mass

Answer 2

Is the mass of an isotope relative to one-twelfth the mass of one atom of carbon-12

Question 3

Relative Formula Mass

Answer 3

Is the sum of the relative atomic masses of all atoms present in its formula

Question 4

Relative Atomic mass symbol

Answer 4

A_r

Question 5

Relative Isotopic Mass symbol

Answer 5

M_r

Question 6

A Mass spectrometer is used to measure two things:

Answer 6

1. The mass of each different isotope of the element
2. The relative abundance of each isotope of the element

Question 7

What are the four steps in a mass spectrometer? (in order)

Answer 7

Ionisation, Acceleration, Deflection, Detection

Question 8

What happens during the ionisation step?

Answer 8

The particles are fed into an ionisation chamber, where they are bombarded with a stream of electrons. These electrons knock one or more electrons out from the sample particles making them positive ions.

Question 9

What happens during the Acceleration step?

Answer 9

An electrical field accelerates the positive ions to a high speed

Question 10

What happens during the Deflection step?

Answer 10

Different ions are deflected by the magnetic field by different amounts

Question 11

What does the amount of deflection (during the deflection step of a mass spectrometer) depend on?

Answer 11

The mass of the ion, lighter ions deflected easier
The charge of the ion, ions with a greater positive charge are deflected easier

Question 12

What happens during the Detection step?

Answer 12

The beam of ions remaining is detected electrically. Only ions with the correct mass/charge make it all the way through the machine.

Question 13

What are the three other uses of the mass spectrometer?

Answer 13

Identifying unknown compounds
Identifying trace compounds in forensic science
Analysing molecules in space

Question 14

Molecular Ion

Answer 14

Is a positive ion formed in a mass spectrometer from the whole molecule

Question 15

Fragmentation

Answer 15

Is splitting of molecules, in a mass spectrometer, into smaller parts

Question 16

One Mole

Answer 16

Is the amount of any substance that contains the same number of particles as their are atoms in exactly 12g of carbon-12

Question 17

Avogadro Constant

Answer 17

Is the number of atoms per mole

Question 18

Molar Mass

Answer 18

Is the mass of one mole of a substance

Question 19

What is the equation for a mole, n?

Answer 19

n = mass/molar mass

Question 20

Stoichiometry

Answer 20

Is the molar relationship between the amounts of reactants and products in a chemical reaction

Question 21

Empirical Formula

Answer 21

Is the simplest formula showing the simplest whole number ratio of the number of atoms of each element present

Question 22

Molecular Formula

Answer 22

Is the actual number of atoms of each element present in the molecule. it is a multiple of the Empirical Formula

Question 23

What are the three steps to calculating the Empirical Formula?

Answer 23

1. Divide the masses or percentage composition by the molar mass
2. Divide all results from step 1. by the smallest result from step 1.
3. Convert these numbers into whole numbers

Question 24

Molar Volume, V_m

Answer 24

Is the volume per mole of a gas

Question 25

What is the equation for concentration, c?

Answer 25

c = n/v

Question 26

1l is equal to how many dm³?

Answer 26

1

Question 27

Atom Economy

Answer 27

mass of product / total mass of reactants x 100

Question 28

Percentage Yield

Answer 28

Mass of product obtained / maximum theoretic mass x 100

Question 29

Percentage Error

Answer 29

error / reading x 100