Home
Common Compounds
Exam Guide
FAQ
Features
Glossary
Construction Kits
Companion Notes
Simulations
Slide Index
Toolbox
Tutorial Index

FAQ
Introduction
Measurement
Matter
Atoms & ions
Compounds
Chemical change
The mole
Gases
Energy & change
The quantum theory
Electrons in atoms
The periodic table
Chemical bonds
Solids
Liquids
 Solutions
Acids & bases
Redox reactions
Reaction rates
Organic chemistry
Everyday chemistry
Inorganic chemistry
Environmental chemistry
Laboratory
History of chemistry
Miscellaneous

 Home FAQ Solutions Print | Comment
 Previous Question Next Question

# How do I compute percent compound in a mixture, given mixture mass and element percents?

If I have 10 g of a solution made up of PCl3 and PCl5 and 81.04% of the mixture by mass is due to Cl, how many grams of PCl3 and PCl5 is there? I don't think there is enough information here!
Ed Tremblay 11/22/99

There are two unknowns (grams of PCl3 and grams of PCl5) so you'll have to write two independent equations to solve the problem. If there's nothing in the mixture but PCl3 and PCl5,

10 g = grams of PCl3 + grams of PCl5

You know that 81.04% of the mass of the mixture is Cl, so there are a total of 8.104 g of Cl in the sample. The total mass of chlorine has to be equal to the mass of Cl in the PCl3 plus the mass of Cl in the PCl5. 77.45% of PCl3 and 85.13% of PCl5 is chlorine, so:

8.104 g Cl = 0.7745 × g of PCl3 + 0.8513 × g of PCl5

Now all you have to do is solve the two equations simultaneously (e. g. solve the first equation for PCl3 and substitute the result into the second equation). Can you take it from here?

Author: Fred Senese senese@antoine.frostburg.edu

General Chemistry Online! How do I compute percent compound in a mixture, given mixture mass and element percents?