Atomic structure, analysis and quantitative chemistry
Mass number = number of protons and neutrons.
Isotopes are atoms of an element with different numbers of neutrons.
The relative formula mass = Relative atomic mass of all atoms in the formula of the compound.
The relative formula mass in grams is one mole of the substance.
Nucleus has protons and neutrons
Electrons are arranged around it in energy levels.
Relative mass of particle
Neutron 1
Proton 1
Electron very small 1/1836
Atomic number = number of protons.
Atoms of an element will have the same number of protons. Atomic number = same.
They can have different neutrons so the mass number changes (isotopes)
Isotopes have identical chemical properties but some are radioactive.
Mr is relative formula mass
Ar is relative atomic mass
One mole of the substance is the Mr in grams.
Method of analysis
Paper chromatography
Used to analyse coloured substances e.g. coloured pigments and artificial colours.
This work as coloured substances have different dissolving rates in liquid and bonding with paper.
Substances that are better at dissolving than bonding with paper travel further.
Substances that travel the same distance with the same colour are likely to be the same.
Instrumental method of analysis
This method uses machines they are:
Fast
Accurate (reliable)
Sensitive (can detect small amounts in a small sample)
Gas chromatography
A mixture of compounds can be separated.
It has a long glass tube called a column with a powdered solid material inside that is put in an oven.
The sample is dissolved in a solvent and then injected into one end of the column.
An unreactive gas usually nitrogen carries the sample through
The different substances travel at different speeds so they are separated.
The separated substances leave the column one after the other, they are detected by a detector.
Peaks show number of compounds
Position of peaks show the retention time for each compound
Mass spectrometry
It identifies substances very quickly and accurately in small amounts.
It provides the relative formula mass of the substances separated by gas chromatography.
The peak furthest to the right is the molecular ion peak. this is the relative formula mass of the substance.
GC is usually linked with MS so substances can be separated and identified
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