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Chapter 6 Chemistry Notes

# Ml conclusion our best measures of amount are counting

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Unformatted text preview: res of amount are counting and mass. (Volume is sometime convenient but must be used carefully. If needed density can be used to convert the volume to mass, and always remember volume is not necessarily conserved) . How are amounts measured in this recipe? volume, mass, and counting are ways that we measure compositions What often happens to volume when you heat or cool a substance? ______________________________ Quick experiment: If you add 75.0 mL of ethanol and 25.0 mL of water, what is the resulting volume? volume, counting, and mass (or weight). Formula Mass (FM) = 2 (1.01 amu) + 1 (16.00 amu) = 18.02 amu Propane C3H8 FW=44.11 amu Ethylene glycol C2H6O2 FW=62.08 amu Wouldn’t it be nice if it were easy to relate # of atoms to mass for macroscopic samples too? 1 9/23/2013 Example: WW-I Chemical Weapon Phosgene gas (COCl2) was used as a chemical weapon during WW-I but now is used as a building block for pharmaceuticals. Scaling is simple: if it works for 1, law of constant composition says it should work for 10 (deka prefix,da) or any other number. It can be made by passing carbon monoxide and chlorine over a carbon catalyst: CO + Cl2 COCl2 An atomic level “cartoon” of this reaction looks like: + Sub-micro to Macro Scale-up + If we want to carry out this reaction (with no leftovers) it would be difficult to measure out 1 molecule of carbon monoxide and 1 molecule of chlorine gas!! So what’s our strategy? By mass: 28 daamu + 71daamu = 99 daamu total. By mass**: (12+16=) 28amu + (2*35.5=) 71amu = 99 amu total. BUT this is still only 1.6x10-21 g. Still too small; we need a lot! The metric prefix for 1024 Yotta (Y) so let’s make 99 Yamu. 99.0 Yamu total mass (recall:1 amu = 1.66x10-24g) Let’s scale up until it is easily measurable! 1024 CO+ 1024 Cl2 1024 COCl2 Thus 99.0 Yamu = 164 g (Easily measurable!) **We will ignore the complication of isotopes for now. The good, the bad, and the ugly… The good: by using a scaling factor of about 1024 (Yotta), the transformation from sub-microscopic quantities to macroscopic quantities was possible. The “Perfect” Scaling Factor Recall: a carbon-12 atom has a mass of exa...
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