Simple Solution #4
Drenthonium
0.20 x 75 g/mol
Borculonium
0.30 x 100 g/mol
Beaverdamium
+
0.50 x 106 g/mol
Zeelandium
98 g/mol
This is called the weighted average mass of the three isotopes of Zeelandium.
The atomic masses on the periodic table are weigh
Your Turn Again:
Calculate the percentage composition for aluminum carbonate. (This means
find the percentage by mass of each element in the compound.)
% Composition for aluminum carbonate
aluminum carbonate is Al2(CO3)3
atomic mass / molar mass
x100
%
2
Empirical Formulas
An empirical formula is the mathematically reduced form of a chemical
formula. Several examples.
Empirical Formulas from Percentages
C4.1b Calculate the empirical formula of a compound based on the weight of
each element in a compound.
Molar Mass of Hydrates
The mass of the water is ADDED to the mass of the salt.
Example
MnBr24 H2O
manganese II bromide tetrahydrate
Mn
2 Br
54.9
2 x 79.9
4 H2O + 4 x
18.0
286.7 g/mol
Remember to ADD the mass of water.
Nomenclature and Formula Mass
Formula
The Percentage Composition Calculation allows us to calculate the
percentage of mass for each element in a compound.
Sodium hydroxide is NaOH.
Na 23.0 g/mol
16.0 g/mol
H
+ 1.0 g/mol
40.0 g/mol
Find The Percentage of Each Element
% Na = 23 x 100 = 57.5 % N
Most Common Isotope
C4.10d Predict which isotope will have the greatest abundance given the
possible isotopes for an element and the average atomic mass in the periodic
table.
For the most precise data, this is an item one would normally look up.
Butif no
30 grams hydrogen sulfate (answer)
Hydrogen sulfate is H2SO4
The molar mass is 98.1 g/mol
30 grams x 1mol
= 0.31 mol H2SO4
98.1 grams
30 grams x 1mol
x 6.022 x 1023 formula units
98.1 grams
1 mol
= 1.84 x 1023 formula units hydrogen sulfate
Your Turn
You
Warm-Downsnot in packet
What is the mass of 6.78x1024 formula units of barium hydroxide?
Plan
Formula units moles grams
6.78x1024 f.u.
1 mol
171.3 g Ba(OH)2
6.022x1023 f.u.
1
1 mol
Warm Downs-not in packet
How many molecules in 1 teaspoon of water?
1 tsp
Simple Sample #2
If 33.3 % of our class weighs 100 lbs, 33.3 % weighs 120 lbs and 33.3 %
weighs 140 lbs what is the average weight?
Simple Sample #3
If 20 % of the textbooks in our school weigh 500 grams each and 80 % weigh
600 grams each, what is the ave
Empirical Formula Example 2
Find the empirical formula of a sample having 37.49 % C, 12.58 % H, 49.93 %
O.
37.49 g C
12.58 g H
49.93 g O
12.011 g/mol
1.0079 g/mol
15.999 g/mol
= 3.121 mol C
12.481 mol H
3.121 mol O
C3.121H12.481O3.121
3.121
3.121
3.121
=