Percent Composition Breaks down the amount of an element in a compound by percentage Total mass of element total mass of compound Result will always be a decimal Multiply by 100 to get the final percentage ID: 920525
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Slide1
Empirical Formulas
Knowing exactly what it is
Slide2Percent Composition
Breaks down the amount of an element in a compound by percentage
Total mass of element / total mass of compound
Result will always be a decimal
Multiply by 100 to get the final percentage
Slide3Practice 1
What is the percent composition of the elements in NaC
2
H
3
O
2
?
Slide4Practice 2
What is the percentage of Oxygen in NH
4
NO
3
?
Slide5Practice 3
What is the percentage of Iron in Iron (III) Carbonate?
Slide6Empirical formulas
Formulas are represented in smallest whole number ratios
Derived from percent composition of a compound
Remember 100g = 100 % for easier calculations
Slide7T
alk it Out…
Change percentage to grams assuming there are 100g of the sample
Divide by the molar mass of each element
Divide the moles of each element by the lowest number of moles of all the elements
Round to whole numbers to find ratios UNLESS there is .5, then multiply each result by 2 for whole number ratios
Slide8Problem 1
The percent composition of a compound was found to be 63.5% Silver, 8.2% Nitrogen, and 28.3% oxygen. Determine the compound’s empirical formula.
Slide9Problem 2
A 170.00g sample of an unidentified compound contains 29.84g of Sodium, 67.49g Chromium, and 72.67g Oxygen. What is the compounds empirical formula?
Slide10Problem 3
A 60.00g sample of an tetraethyl lead, a gasoline additive, contains 38.43g of Lead, 17.83g Carbon, and 3.74g Hydrogen. What is the compounds empirical formula?
Slide11Molecular Formula
You must have the empirical formula first
You must calculate the mass of the empirical formula
Don’t lose track of your numbers!
Slide12Calculate empirical formula
Calculate the mass of the empirical formula
Divide the given mass by the empirical mass, this will give you an element multiplier
Multiply your chemical quantities by the multiplier
Rewrite molecular formula with new chemical values
Slide13Problem 1
Determine the molecular formula of a compound with an empirical formula of NH
2
and a formula mass of 32.06
amu
.
Slide14Problem 2
The empirical formula of a hydrocarbon is found to be CH. Laboratory procedures have found that the molar mass of the compound is 78 g/mol. What is the formula of this compound?
Slide15Problem 3
A compound containing
50.05
% Sulfur
and
49.95% Oxygen
has a molar mass of
256.28 g/mol
. Determine the empirical and molecular formula of this compound.