Studied by 3 people
Avogadros Constant
1 mol = 6.02 × 10²³ atoms of that element
Avogadro’s equation
n = N/NA
n is number of mols
N is the given number of elements (or the number of elements you have to find out)
Na is the Avogadro’s constant
Relative moldecular mass, Mr
Adding the Mass number (M) for each element (e.g H20 has 2×1.01 + 16)
It has no units, unlike molar mass, M which is gmol-1
How to find number of element in compound (e.g how many H atoms in H20)
Find the number of mols for the compund, multiply by the number of that element in the formula (e.g times by two for H20 because 2 H atoms)
Then times by Avogadro’s constant.
Calculating Empirical Formula
It is the smallest ratio of elements (eg H20 —> HO)
To calculate:
1) Let mass of compund = 100g and let the percentage of each element = the mass of each element (eg 75% = 75g of Fe)
2) Calculate n of each element and find simplest ratio (this is empirical formula)
Percentage Composition
How much of each element is in the compound
1) Let n of compund = 1 mol
2) m = M x n for each element (remember to times number of moles by 2 if there is 2 of the element eg H2)
3) mass of one element / total mass x 100% gives pecentage for one element
4)100 - percentage for the composition of the other element
Molecular Formula
How many there actually is
eg: CxHy ←x and y values will be given, or empirical formula
{ (12.01 x) + (1.01 y) }
Given mass / { } = a rough whole number, times x and y by this to get molecular formula
