Chemical calculations
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What is the relative atomic mass?
The average mass of one atom of the element relative to one-twelfth the mass of one atom of carbon-12.
What is the relative isotopic mass?
The average mass of one atom of the isotope relative to one-twelfth the mass of one atom of carbon-12.
What is the relative formula mass?
The average mass of one atom of a molecule relative to one-twelfth the mass of one atom of carbon-12.
What are the steps in the mass spectrometer process?
• Vaporisation- sample is heated • Ionisation- gaseous sample is fired with electrons to form positive ions • Acceleration- an electric field accelerates the ions to high speeds • Deflection- a magnetic field deflects ions according to the mass:charge ratio • Detection- ions with the correct ratio pass through and are recorded
What are some other uses for mass spectrometry?
Identifying unknown compounds Identifying trace compounds in forensic science Analysing molecules in space
Why is the mass spectrometry process done in a vacuum?
To prevent collision with air molecules.
What is the mole?
The amount of any substance that contains the same number of particles as there are atoms in exactly 12g of carbon-12.
What is the Avogadro’s constant?
The number of atoms in 12g of carbon-12.
What is the molar mass?
The mass of one mole of a substance.
What is empirical formula?
The simplest whole number ratio of the amount of elements present.
What is molecular formula?
The actual number of atoms of each element present in the molecule.
What is atom economy?
(Mr of the desired product/ Mr of all reactants) x100
What is % yield?
(Mass of product obtained/ Maximum theoretical mass of product) x100
How to find moles?
Mass (g)/ Mr
What are the reasons for a reaction not producing the maximum percentage yield?
*The reaction may be reversible *Side reactions occurring *Product lost in transfer
What is the ideal gas equation?
Pressure x volume = n x gas constant x temperature
How to convert Celsius to Kelvin?
Celsius + 273
How to find volume?
Number of moles/ concentration
How to find the concentration of a solution?
Concentration = moles / volume
How to calculate relative atomic mass from a mass spectrometer?
(% abundance x mass/charge ratio) / 100
How to calculate percentage error of an apparatus?
Uncertainty/reading x100
How to correct gas volumes due to changes in temperature or pressure?
P1V1/T1 = P2V2/T2 (change C to K).
How to calculate the largest percentage error?
largest resolution / smallest reading x100.
How to calculate percentage errors with multiple readings?
Resolution / reading x100 then multiply by number of readings.