2.1 Foundations In Chemistry 2.1-3.4 Flashcards
Isotopes
Atoms of the same element with different numbers of neutrons
1 picometer
1 x 10^-12 m
One trillionth of a metre
Physical and chemical properties of isotopes
Chemical properties stay the same because electronic configuration doesn’t change
Physical properties of the isotopes are influenced by the number of neutrons so are different (mass)
Relative masses of p n and e
P 1
N 1
E 1/1800 (~0)
Relative charges of p n and e
P +1
N 0
E -1
Mass spectrometer
A machine that chemists can use to determine the relative atomic mass or relative molecular mass, the molecular formula, and the structure of compounds
What does a mass spectrometer do
Sorts positively charged ions according to their mass and charge
4 stages of mass spectrometry
Ionisation
Acceleration
Deflection
Detection
Stage 1 Ionisation mass spectrometry
A sample is placed in the mass spectrometer, if it’s not already a gas it’s vaporised
The atoms or molecules diffuse into the path of electrons from the electron gun and are ionised
X(g) —> M^+(g) + e^- Or
X(g) + e^- —> X^+ (g) + 2e^-
+2 ions can be formed but are not as common as more energy is required to knock out two electrons
Stage 2 acceleration mass spectrometry
A negative electric field is used to accelerate the beam of positive ions, and skits are used to narrow the beam
Stage 3 deflection mass spectrometry
A strong magnetic field is used to deflect the positive beam
The amount each ion is deflected by depends on the mass to charge ratio, m/z
A small m/z ratio creates a larger deflection
By varying the magnetic field, ions of different m/z ratio can travel along the centre of the mass spectrometer
Stage 4 detection mass spectrometry
When an ion reaches the detector it produces a tiny current which is noted as one ion with a specific m/z ratio
This is true for all the ions that reach the detector
Hence the proportion of each ion in the sample is recorded and the spectrum is printed
Ar Definition
Average mass of an element relative to 1/12 of carbon-12
Mr definition
Average mass of a molecule or compound relative to 1/12 of carbon-12
Avogadro constant
The number of particles in each mole of carbon 12
6.02 x 1023 atoms
One mole of carbon atoms has a mass of…
12g
One mole of hydrogen atoms has the mass of…
1g
Molar mass
Gives a convenient way of linking moles with mass
C = 12.0 g mol-1
Gives the mass in grams in each mol of the substance
Molecular formula
The number of atoms of each element in a molecule
Empirical formula
Simplest whole number ratio of atoms of each element in a compound
Anhydrous
Without water
Hydrated
With water
Heating copper sulphate
Turns it from blue to white
The blue form contains water (hydrated copper sulphate)
The white form contains no water (anhydrous copper sulphate)
Heating copper sulphate word equation
Hydrated copper sulphate <==> anhydrous copper sulphate + water
Water of crystallisation
Compounds crystallised from water contain water molecules within the structure. The water is called water of crystallisation
Different compounds may contain different amounts of water of crystallisation
What do we use to show how many molecules of water are associated with the compound (water of crystallisation)
We use a floating . followed by a number
1cm3=?ml
1ml
1ml=?cm3
1cm3
Concentrated definition
A large amount of solute per dm3
Dilute definition
A small amount of solute per dm3
Weighing by difference
Weigh the empty wearing boat
Weigh out the desired amount onto it and record the mass (A)
Empty the weighting boat into a beaker
Reweigh the weighing boat and record its mass (B)
Do this sum B-A to work out the mass taken
Molar gas volume
One mole of any gas occupies 245dm or 24000cm3 at room temperature and pressure
1litre=?dm3
1dm3
1dm3=?litre
1litre
Ideal gas equation
pV=nRT
Pressure of gas (Pa) x volume of gas (m3) = no of moles of gaseous particles x gas constant x temp (kelvin)
What’s the gas constant
8.31 J K-1 mol-1
Absolute zero kelvin
-273oC
Stoichiometry
In a balanced equations the balancing numbers give the ratio of the amount, in moles, of each substance
This ratio is called the stoichiometry of the reaction
%yield
Actual yield / theoretical yield x 100
Atom economy
Measure of how well atoms have been utilised
Mass of desires product / total mass of reactants x 100
