Chemical Calculations - Mass spectroscopy Flashcards
What must be done to prepare the mass spectrometer?
It has to be evacuated to prevent collisions with air molecules.
What is the function of a mass spectrometer?
To determine molecular and atomic masses.
What is the first stage of mass spectroscopy?
The gas molecules are ionised by bombarding them with electrons, knocking off one or more electrons from the gas atoms or molecules to form positive cations.
What is the second stage of mass spectroscopy?
The ions are accelerated by an electric field.
What is the third stage of mass spectroscopy?
They are deflected by a magnetic field. Heavier ions are deflected less than light ones so that ions of different mass-charge ratios may be detected and measured separately.
What are the uses of mass spectroscopy?
1 - the determination of elation isotopic mass and abundance which allows us to find an elements Ar
2 - The measurement of the relative molecular masses of molecules and the determination of their structure.
3 - Qualitative and quantitative analysis analysis of mixtures and the identification of trace compounds.
How do you use a mass spectrum reading to calculate Ar?
Multiply the relative abundance by the m/e reading for each peak to find the total amount of each isotope present and add them together. Then divide by the total relative abundance. To give a value for Ar. Give answer to 3 s.f.
How do you calculate empirical formula?
Calculate the number of moles of each element or molecule present by dividing the mass or percentage of that substance by its Ar. Then divide through by the smallest to find the simplest ratio.
What is a molecular formula?
A simple multiple of the empirical formula to give the correct numbers of each element In the molecule rather than the ratios of those molecules.
How do you work out the molecular formula?
By finding out which formula gives the correct molar mass (Ar)
