1.3 - Chemical Calculations Flashcards
Define Relative Atomic Mass
The average mass of one atom of the element relative to 1/12 of the mass of one atom of Carbon-12
What is the unit for rel atomic mass?
No units - All comparative
What does mass spectrometry measure?
The mass of each isotope of the elemetn
The relative abundance of each isotope of the element.
What are the six stages of mass spectrometry?
1) Vaporisation
2) Ionisation
3) Acceleration
4) Deflection
5)Detection
6) Vacuum
What state are atoms in the mass spectrometer?
Vaporised
Describe the second stage of Mass Spec
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-
Describe the third stage of mass spec
Plates at a high negative voltage accelerates the ions.
Describe the fourth stage of mass spec
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
What is the fifth stage of the mass spec?
Detection
Why does the mass spectrometer require a vacuum?
Air would be detected
The particles would hit air molecules
How do you calculate atomic mass from mass spec data?
100
Chlorine Ratios istopes
35Cl & 37Cl 3:1
Diatomic - 70 - 72 - 74
9:6:1
Bromine Isotope Ratio
Br - 79 & 81 1:1
Diatomic Br2 - 158/160/162
1:2:1
Define Mole
The amount of any substance that contains the same amount of particles as there are atoms in 12.0g of Carbon-12
Formula for Mols
n = m/M mass(g)
mols (mol-1) = ————
Molar mass (g mol-1)
Define Empirical Formula
The simplest formula,showing the simplest whole number ratio of the number of atoms of each element present
Define Molecular formula
Shows the actual numbers of atoms of each element present in the molecule. It is a multiple of the empirical formula.
What volume of gas at room temp?
At room temperature and pressure (25C and 1atm) one mole of gas occupies 24.5dm3
Describe Boyle’s Law
V α 1/p Volume of gas is inversely proportional to pressure.
Describe Charle’s Law
V α T Volume is directly proportional temperature
Ideal Gas Equation
pV = nRT
Units of the Ideal Gas Equation
p = pressure = Pascals
V = volume = M3
R = Gas constant = 8.31jk-1mol-1
T = Temperature = Kelvin
Cm3 to M3
x1million
Equation for atom economy
(Mass of required product/Total mass of reactants) x 100
Equation for % yield
Mass Obtained / Theoretical Yield x100
Gas equation for finding a difference?
P1 V1 P2 V2
——– = ——— (T must be Kelvin)
T1 T2
How do you make a standard solution?
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.
Concentration Equation
n = c x v/1000
How do you calculate percentage error?
percentage error = error/reading x100
What is the error on a burette?
+- 0.05
