Chapter 7 - MOLES Flashcards
How much is one mole?
6.02 x 10^23
What is Avogardro’s Constant
6.02x10^23
What are the parts of #=n*N
# = # of particles n = # of moles N = 6.02x10^23
What are the parts of m=n*M
m = mass (grams) n = # of moles M = molar mass
What’s the law of Constant Composition
Elements in a compound present in the same proportion by mass
Elements that combined together to form compound can be found in different proportions but will make different compounds
Eg) carbon and hydrogen can combine to form C6H6, they are found in different proportions in different compounds
Percentage composition “by mass”
% of an element = (mass of that element/mass of the compound) x 100%
Percentage composition “by chemical formula”
% of an element= ((mass of element) * # of atoms in one molecule/mass of compound)x100
What is an Empirical formula
Gives the relative number of atoms each element that makes up the compound
How do you find the empirical formula
Element | ?
Givens | m= \_\_\_g
| M=\_\_g/mol
n=m/M | \_\_\_mols
div by smallest # | /What are 2 rules when finding the empirical formula
- round the answer to a # with either a .0 or 0.5
- if you end up with a # with .5 multiply all #s by 2.
How to find the Molecular formula
Calculate the empirical formula
Find the molar mass of the empirical formula (M-EF)
Divide the actual molar mass by the molar mass of the empirical formula
Multiply this subscripts in the empirical formula by this value
Eg) M of H2O
= 2(H) + 1(O)
= 2(1) + 1(16)
= 18.0 g/mol
How do you find the mass
m = n * M
Mass = #ofmoles x molarmass
How do you find the number of moles
n = m/M
= mass divided by molar mass
