What is the weight of one atom of carbon 12?
1.99x10^-23 grams or 12 amu
Define: atomic mass unit
- how much is 1 amu in grams?
a unit of mass
1 amu = 1.66x10^-24 grams
Define: mass spectrometry
- experiment used to determine atomic mass
- sample is placed in a curved tube where it enters a magnetic field causing the ions to bend around the curve and hit a metal plate
- the larger the ion, the stronger the magnetic field must be to cause deflection
- this separates ions by their mass to charge ratio
How does a luggage hand held detector check for explosives?
- tests for the mass of known explosives
How do you calculate atomic weight of an element?
- consider the relative abundances of the isotopes and add to create the average atomic mass
define: mole
unit of measurement used for counting atoms
- relates the number of atoms to a mass of a sample
define: avogadro’s number
- number of atoms in 1 mole of something
- 6.022137x10^23
Define: molar mass
mass in grams of 1 mole of that substance
Define: mass percent
the mass of an element in a compound expressed as a % of the total mass of the compound
Define: elemental analysis/ combustion analysis
- finding out the molecular composition (empircal formula) of a sample
- elemental analysis: burning a sample in the presence of O2 and determining the percent of carbon and hydrogen from the masses of CO2 and H2O
Define: molecular formula
- how can we determine this
exact # of atoms in one molecule of the compound
- mass spectrometer
Define: empirical formula
- how can we determine this
the formula that expresses the smallest whole number ratio of atoms in a compound
- elemental analyzer
Define: limiting reagent
- reactant that is used all up
Define: theoretical yield
- amount of product created from a reaction assuming all of the limiting reagent is used up
Give the formula for percent yield
actual yield (g)/ theoretical yield (g) x 100%
What are some reasons why we don’t obtain exactly theoretical yield
- reaction conditions may not be optimal
- reaction may happen very slow
- side reactions may occur
- difficult to isolate all products in pure form
Why is percent yield important to know
- gives information on how well the reaction is working
- change conditions of the reaction and monitor an increase or decrease in the % yield
