Major Points• Finding amu (atomic mass unit)
• Conversions (atoms-->amu, atoms--->grams, grams--->atoms) • The Mole (conversions) • Percent Composition (finding how space much an element takes up in a compound, percent-wise) • Molecular formula vs. Empirical formula • Calculating Empirical formulas • Calculation Molecular formulas Rounding Rules for Empirical Formulas
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Example Problems1. You have 6.43x10^43 atoms of Fe. What is the amu?
Answer: 3.59 x 10^45 amu Fe 2. You have 2.34x10^15 atoms of Ni. How many grams of Ni are there? Answer: 2.28x10^-7 g Ni 3. You have 63.72 grams of FeCl2. Find the number of atoms in FeCl2. Answer: 3.03x10^23 atoms FeCl2 4. In the compound HCLO3, what is the percent of oxygen? Answer: 56.83 % O 5. In the compound HCLO3, what is the percent of chlorine? Answer: 41.98% Cl 6. An oxide of aluminum is formed by the reaction of 4.151g Al with 3.692g O. Calculate the Empirical formula. Answer: Al2O3 Tip: If no sample size is given while calculating Empirical formula, you can choose any number... but I always use 100!
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Conversions:
1 amu = 1.66x10^-23 g * Find amu by looking for molar mass of the compound/element
Converting between grams and moles- use molar mass
Converting between atoms and moles- use Avogrado's number, 6.022x10^23
Converting between volume and moles- use 22.4 L = 1 mole
Online Resources
Finding Empirical Formula (Use our rounding rules!): http://www.chem.tamu.edu/class/majors/tutorialnotefiles/empirical.htm
Determining Empirical and Molecular Formulas: http://www.wisc-online.com/objects/ViewObject.aspx?ID=GCH7204
Percent Composition: http://www.chem.tamu.edu/clas s/majors/tutorialnotefiles/percentcomp.htm
Determining Empirical and Molecular Formulas: http://www.wisc-online.com/objects/ViewObject.aspx?ID=GCH7204
Percent Composition: http://www.chem.tamu.edu/clas s/majors/tutorialnotefiles/percentcomp.htm
Video Resources
Determining the Empirical Formula from an Elemental Analysis: http://chemcollective.org/activities/tutorials/stoich/ef_analysis
Finding Empirical Formula with a word problem (by me!): https://vimeo.com/57180116
Finding Empirical Formula with a word problem (by me!): https://vimeo.com/57180116
Activity Resources
Percent Composition worksheet: http://oi46.tinypic.com/mljcck.jpg
Empirical and Molecular Formulas Worksheet: http://oi46.tinypic.com/t9i42f.jpg
Empirical and Molecular Formulas Worksheet: http://oi46.tinypic.com/t9i42f.jpg