Quantitive chemistry Flashcards
Empirical formula
the simplest whole number ratio of atoms of each element in a compound
percentage mass
( number of atoms of X in compound times AR of X
____________________________________________
total mr of compound
times that by 100
the mole
One mole of any substance contains 6.02 x 10 squared to 23
mass of mole
the mass of one mole of a substance is equal to the Ar/ Mr of the substance weighed out in grams
relative atomic mass
is the mass of the atom compared with that of the carbon-12 isotope, which has a mass of exactly 12, and it is the weighted mean of the mass numbers
the principle of conversion of matter
implies that matter cannot be created or destroyed, although it may be rearranged in space and changed into different types of particles
Percentage yield
During a chemical reaction, the calculated number of moles of product formed is called the theoretical yield since it is the number of moles that you would expect to be formed from the masses of reactants involved
many chemical reactions, however do not give the expected amount of product and the amount of product that is obtained from actually doing the experiment is called the actual yield.
percentage yield
actual yield
_____________
theoretical yield x 100
Reasons why percentage yield may not be 100 percent
loss of product by transfer
side reactions may occur
reaction is reversible
reaction is not complete
loss of product when separating it from the reaction mixture
molecular formula
actual number of atoms of each element in a compound
water of crystallization
water that is chemically bonded into the crystal structure
degree of hydration
refers to the number of moles of water of crystallisation that is chemically bonded in 1 mole of that compound
percentage of water in a compound
degree of hydration x Mr of H2O
_____________________________
total Mr of compound x 100
thermal decomposition
the substance being broken down by heating
method
weigh an empty crucible
put approx. 4 grams of the hydrated salt into crucible and record the mass of the crucible and hydrated salt
set up apparatus as shown below
heat crucible and its contents gently for a few minutes, allow to cool and then reweigh
continue heating and reweighing the crucible until the mass does not change any further ( indicating all the water of crystallisation has been removed)
what happens if we don’t heat to constant mass
the decrease in mass would not be great enough( since not all the water has been removed) meaning that our calculated value for water of crystallisation would be lower than expected
what would happen if we heat too strongly
the anhydrous compound may start to decompose which result in an even greater loss in mass than expected, meaning we would get a higher than expected value for the amount of water of crystallisation
how to find mass of of hydrated salt
mass of crucible and the hydrated salt- mass of empty crucible
mass of anhydrous salt
mass after heating to constant mass- mass of empty crucible
mass of water of crystallisation
mass of hydrated salt - mass of anhydrous salt
