C9 QUANTITATIVE CHEMISTRY Flashcards
molecular formula
gives the number of atoms element present in a molecule
empirical fromula
give the number of atoms of each element present in a compound as the simplest whole number ratio
converting molecular to empirical formulae
divide the number of each atom by the highest common factor of all of the atoms
molecular to empirical formulae examples
C2H4- ch2 (divided by 2)
C6H1206-CH20 (divided by 6)
relative atomic mass , A
the mass of an atom relative to 1/12th the mass of carbon-12. No units
relative formula mass , Mr
the mass of one unit of a formula, found by adding the relative atomic masses of all of the atoms in it
to calculate the empirical formulae from experimental data
write each elements symbol with a ratio : symbol between
write out the amount of each element from the questions
divide each amount by the Ar of the element
divide each answerably the smallest answer to get a ratio
write the empirical formulae
to find a molecular formula from an empirical formulae
calculate Mr for the empirical formulae
divide the Mr of the molecular formulae by this number
multiply the empirical formula by your answer
conservation of mass
the total mass of products must equal the total mass of reactants
precipitation reaction
a reaction that produces a solid precipitate by mixing two solutions
closed system
a system in which no chemicals can enter or leave , such as a sealed tube
open system
a system in which chemicals can enter or leave - such as an open test tube
conservation of mass in a closed system
no atoms are able to enter or leave , so the total mass stays the same - for example a precipitation reaction in a closed flask
conservation of mass in an open system
for example , a carbonate reacting with acid producing CO2 bubbles : the mass appears to decrease because you can’t weigh the gas that goes into the air, however it is still there
excess reactant
any reactant which is not used up completely in a reaction because there is more of it than needed
limiting reactant
any reactant of which is completely used up in a reaction the limiting reactant determines how much product is made
calculating reacting masses
write out the balanced equation
write the mass of he chemical you are given, and m for the mass you are finding under their symbols
draw a line underneath the masses to make it a division
calculate the Mr of each multiply by the big numbers and write under the line
puts an equals sign between the two or form an equation
solve for m
moles
the unit of measurement of chemicals - one mole of any chemicals is the same amount
one mole
an amount of a chemical such that one mole has a mass in grams that is the same as its relative formula mass
Avogadros constant
6.02 x 10- 23 the number of atoms / molecules present in one mole of a substance
calculating moles from mass
quantity in moles = mass / relative formula mass
calculating moles from a number of particles
quantity in moles = number of particles / 6.02 x 10-23
calculating number of particles from a mass of substance
number of particles = (mass/relative formula mass) x 6.02 x 10-23
stoichometry
the ratio of the number of moles of each substance involved in a reaction
stoichometric coefficient
the big numbers written in a balanced equation
deducing stoichometry
calculate the number of moles present of each of the reactant ( or products )
find the simplest whole-number ratio
balance in the normal way to find the numbers of products (or reactants)
