1.3 - Chemical Calculations

Question 1

Define Relative Atomic Mass

Answer 1

The average mass of one atom of the element relative to 1/12 of the mass of one atom of Carbon-12

Question 2

What is the unit for rel atomic mass?

Answer 2

No units - All comparative

Question 3

What does mass spectrometry measure?

Answer 3

The mass of each isotope of the elemetn
The relative abundance of each isotope of the element.

Question 4

What are the six stages of mass spectrometry?

Answer 4

1) Vaporisation
2) Ionisation
3) Acceleration
4) Deflection
5)Detection
6) Vacuum

Question 5

What state are atoms in the mass spectrometer?

Answer 5

Vaporised

Question 6

Describe the second stage of Mass Spec

Answer 6

Ionisation - The sample passes into an ionisation chamber, where it is bomarded by a stream of electrons (From a HEATED FILAMENT). These collisions knock electrons out of the sample creating positive ions.
M(g) —-> M+ (g) e-

Question 7

Describe the third stage of mass spec

Answer 7

Plates at a high negative voltage accelerates the ions.

Question 8

Describe the fourth stage of mass spec

Answer 8

The ions are deflected by a magnetic field, depending on their m/z ration. (mass/charge)
Lighter ions deflect more & higher charges deflect more
The strength of the magnetic field can be altered to ensure the ion reaches the detector

Question 9

What is the fifth stage of the mass spec?

Answer 9

Detection

Question 10

Why does the mass spectrometer require a vacuum?

Answer 10

Air would be detected
The particles would hit air molecules

Question 11

How do you calculate atomic mass from mass spec data?

Answer 11

                              100

Question 12

Chlorine Ratios istopes

Answer 12

35Cl & 37Cl 3:1

Diatomic - 70 - 72 - 74
9:6:1

Question 13

Bromine Isotope Ratio

Answer 13

Br - 79 & 81 1:1
Diatomic Br2 - 158/160/162
1:2:1

Question 14

Define Mole

Answer 14

The amount of any substance that contains the same amount of particles as there are atoms in 12.0g of Carbon-12

Question 15

Formula for Mols

Answer 15

n = m/M mass(g)
mols (mol-1) = ————
Molar mass (g mol-1)

Question 16

Define Empirical Formula

Answer 16

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

Question 17

Define Molecular formula

Answer 17

Shows the actual numbers of atoms of each element present in the molecule. It is a multiple of the empirical formula.

Question 18

What volume of gas at room temp?

Answer 18

At room temperature and pressure (25C and 1atm) one mole of gas occupies 24.5dm3

Question 19

Describe Boyle’s Law

Answer 19

V α 1/p Volume of gas is inversely proportional to pressure.

Question 20

Describe Charle’s Law

Answer 20

V α T Volume is directly proportional temperature

Question 21

Ideal Gas Equation

Answer 21

pV = nRT

Question 22

Units of the Ideal Gas Equation

Answer 22

p = pressure = Pascals
V = volume = M3
R = Gas constant = 8.31jk-1mol-1
T = Temperature = Kelvin

Question 23

Cm3 to M3

Answer 23

x1million

Question 24

Equation for atom economy

Answer 24

(Mass of required product/Total mass of reactants) x 100

Question 25

Equation for % yield

Answer 25

Mass Obtained / Theoretical Yield x100

Question 26

Gas equation for finding a difference?

Answer 26

P1 V1 P2 V2
——– = ——— (T must be Kelvin)
T1 T2

Question 27

How do you make a standard solution?

Answer 27

1) Dissolve the required mass of the solid in a beaker with deionised water.
2) Transfer into a volumetric flask using a funnel.
3) Rinse the beaker, stirring rod and funnel with deionised water and transfer the washings. (3x)
4) Fill the flask to the line with deionised water, using a pipette for the last drops.
5) Stopper the flask and invert to mix.

Question 28

Concentration Equation

Answer 28

n = c x v/1000

Question 29

How do you calculate percentage error?

Answer 29

percentage error = error/reading x100

Question 30

What is the error on a burette?

Answer 30

+- 0.05