Advanced Chemistry
Mrs. Klingaman
Chapter 7:
Chemical
Formulas &
Compounds
(Part 2)
Name: _______________________________________
Mods:
______________________
Formula Weight Practice
Directions: Determine the formula mass as well as the name or formula (respectively) of the
compounds below:
1) N2O5
Name: _______________________________________
Formula Mass:
2) FeCO3
Name: _______________________________________
Formula Mass:
3) Ca(C2H3O2)2
Name: _______________________________________
Formula Mass:
4) (NH4)3PO3
Name: _______________________________________
Formula Mass:
5) Phosphoric acid
Formula: _______________________________________
Formula Mass:
6) Copper (II) sulfate
Formula: _______________________________________
Formula Mass:
7) Disilicon hexabromide
Formula: _______________________________________
Formula Mass:
In-Class Examples: Percent Composition
The percent by mass of an element in a compound is the number of grams of the element
divided by the number of grams of the compound, multiplied by 100.
Think “part” over “whole”.
% by mass A=
(atomic mass of element A) (# of atoms of element A)
x 100
molar mass of whole compound
1) Magnesium Nitrate
% Mg: _____________
2) Nitrous acid
% H: _____________
3) Aluminum dichromate
% Al: _____________
Formula: _______________________
% N: _____________
% O: _____________
Formula: _______________________
% N: _____________
% O: _____________
Formula: _______________________
% Cr: _____________
% O: _____________
Formula Weight and Percent Composition Practice
Directions: Calculate the molar mass for the following compounds and find the percent by
mass of each element in the compound.
1) FeCrO4
Compound Name: ___________________________________________
% Fe: _____________
2) CuSO3
% O: _____________
Compound Name: ___________________________________________
% Cu: _____________
3) KNO3
% Cr: _____________
% S: _____________
% O: _____________
Compound Name: ___________________________________________
% K: _____________
4) Ca3(PO4)2
% Ca: _____________
% N: _____________
% O: _____________
Compound Name: _____________________________________
% P: _____________
% O: ____________
In-Class Examples: Conversions Using the Mole
Example Calculations (with dimensional analysis):
1. Grams  Moles
How many moles are there in 1.1 grams of iron (III) chloride?
Chemical Formula: _____________________________
2. Moles  Grams
What is the mass, in grams, of 21.3 moles of dichromic acid?
Chemical Formula: _____________________________
3. Moles  Atoms or Molecules
Find the number of molecules in 3.2 moles of barium carbonate.
Chemical Formula: _____________________________
In-Class Examples: Conversions Using the Mole
4. Atoms or Molecules  Moles
How many moles are there in a sample of 1.25 x 1023 molecules of beryllium acetate?
Chemical Formula: _____________________________
5. Gram  Atoms or Molecules
Find the number of molecules in 60 grams of lithium oxalate.
Chemical Formula: _____________________________
6. Atoms or Molecules  Grams
What is the mass, in grams, of 3.24 x 1023 molecules of xenon hexafluoride?
Chemical Formula: _____________________________
Converting Grams  Moles:
Directions: Find the number of moles in each of the following.
1)
79.2 grams of potassium sulfate
Formula: ___________________________
2)
208 grams of sodium bicarbonate
Formula: ___________________________
3)
111.3 grams of sulfur hexafluoride
Formula: ___________________________
Converting Moles  Grams:
Directions: Find the number of grams in each of the following.
4)
6.5 moles of tin (II) cyanide
Formula: ___________________________
5)
3.8 moles of tricarbon octahydride
6)
9.3 x 10–3 moles of silver
Formula: ___________________________
Formula: ___________________________
Converting Moles  Atoms or Molecules:
Directions: Find the number of atoms or molecules in each of the following.
7)
4.0 moles of phosphorous triiodide
8)
5.9 moles of mercury
9)
1. 2 moles of beryllium dichromate
Formula: ___________________________
Formula: ___________________________
Formula: ___________________________
Converting Atoms or Molecules  Moles:
Directions: Find the number of moles in each of the following.
10)
1.7 x 1023 molecules carbon dioxide
11)
3.3 x 1022 atoms of arsenic
12)
8.6 x 1024 molecules of hydroiodic acid
Formula: ___________________________
Formula: ___________________________
Formula: ___________________________
Converting Grams  Atoms or Molecules:
Directions: Find the number of atoms or molecules in each of the following.
13.)
24 grams of iron (III) fluoride
14)
450 grams of sodium nitrite
15)
122 grams of selenium
Formula: ___________________________
Formula: ___________________________
Formula: ___________________________
Converting Atoms or Molecules  Grams:
Directions: Find the number of grams in each of the following.
16)
7.4 x 1023 molecules of silver nitrate
17)
4.5 x 1022 molecules of lead (II) acetate
Formula: ___________________________
18)
9.2x 1025 molecules of calcium bromate
Formula: ___________________________
Formula: ___________________________
Mixed Review of Gram MoleAtom or Molecule Conversions
1)
How many grams are there in 3.3 x 1023 molecules of dinitrogen hexoxide?
2)
How many molecules are there in 4.23 moles of ammonium hydroxide?
3)
How many grams are there in 0.92 moles of boron trichloride?
4)
How many moles are there in 4.5 x 1022 molecules of barium nitrite?
5)
How many moles are there in 9.34 grams of lithium chloride?
6)
How many grams do 4.3 x 1021 molecules of uranium hexafluoride weigh?
7)
How many molecules are there in 230 grams of ammonium hydroxide?
In-Class Examples: Determining Empirical Formulas
Problem #1: An experiment uses a catalyst that is 23.3 % cobalt, 25.3 % molybdenum, and
51.4 % chlorine. What is the empirical formula of this catalyst?
Step #1: Percent to mass  Assume that you are working with a 100 gram sample, so the % of
each element is equal to the mass of each element in grams
Step #2: Mass to mole  Convert the mass of each element to moles of each element using the
molar mass.
Step #3: Divide by small  Divide each of the mole quantities by the smallest number of moles.
Often, this will result in whole or practically whole numbers
Step #4: Multiply ‘till whole  If step #3 does not result in whole numbers, find the least common
multiple that will achieve all whole numbers. These whole numbers represent the
subscripts for each element in the empirical formula.
The empirical formula for this compound is: ________________________________
Problem #2: What is the empirical formula for a molecule containing 65.5% carbon, 5.5%
hydrogen, and 29.0% oxygen?
Determining Empirical Formulas
1) Find the empirical formula of a molecule containing 18.7% lithium, 16.3% carbon, and
65% oxygen.
2) The percent composition of acetic acid is 39.9% carbon, 6.7% hydrogen, and 53.4%
oxygen. Determine the empirical formula of acetic acid.
3) The compound benzamide is composed of 69.40% carbon, 5.825% hydrogen, 13.21%
oxygen, and 11.57% nitrogen. What is the empirical formula of benzamide?
4) Upon analysis, rubbing alcohol (also known as isopropyl alcohol) is found to contain
60.0% carbon and 13.4% hydrogen with the remaining percent due to oxygen. Find the
empirical formula of rubbing alcohol.
5) A certain compound is 47.05% potassium, 14.45% carbon, and 38.5% oxygen. What is
the empirical formula for this compound?
6) Nitrogen and oxygen form an extensive series of oxides with the general formula N XOY.
One of them is a blue solid that comes apart, reversibly, in the gas phase. It contains
36.84% N with the remaining percent coming from O. What is the empirical formula of this
oxide?