Calculations Flashcards
Avogadro’s number
6.02x10^23
calculating relative formula mass
Add all masses of the atoms together
E.g. H2O = (1x2) + 16 = 18
Calculating percentage mass
Divide the At of an element by the Me of the compound
E.g. percentage mass of hydrogen in H2O?
2/18
= 11%
calculating number of moles
n = mass / Mr or Ar
calculating number of particles
number of mole x avagadro’s number
to balance equations
write a ratio to draw how many of what elements are in each side of the equation
balance the equation by making the number of elements on both sides the same
limiting reactant
the element in the equation that has been used up
excess reagent
the element in the equation that has been left over
to deduce the limiting reagent
find the ratio of said elements in the equation
use the table method to find the number of moles
the inaccuracy in the number moles based on the ratio should tell you which element is the limiting and excess reagent
e.g moles for hydrogen is 0.5
moles for oxygen is 0.2
but the ratio is 2:1
the number of moles in oxygen should be 2.5 moles
therefore, oxygen is the limiting reagent
empirical formula
original formula
to calculate empirical formula
use the table method to find the number of moles
divide the number of moles by the smallest number of moles in the compound
e.g. oxygen has 3 moles
hydrogen has 6 moles
you would do 3/3 for oxygen
you would do 6/3 for hydrogen
after calculating this, the answer should be the number of elements for the empirical formula
if you get a decimal place, multiply all numbers until all numbers are whole
concentration
the amount of solute dissolved in a given volume
calculation concentration
C(g/dm^3) = M / Volume(dm^3)
converting cm^3 to dm^3
x by 1000
stoichiometry
balance the equation
