The Vespiary

The Hive => Newbee Forum => Topic started by: pink_dust_angel on June 08, 2004, 05:48:00 PM

Title: 100%(benzene) = ???moles/dm^3 ??????
Post by: pink_dust_angel on June 08, 2004, 05:48:00 PM

ok say swim has some 100% pure benzene, what is the molarity of this?
how does 1 work out the molarity of a pure substance knowing only the number of moles present?
swim only knows the following calcs:
   Moles= mass(g)/molar mass
   Moles= volume(dm^3) x moles/dm^3
this leaves swim with 2 unknowns (if swim only knows how many moles are present)

Title: You need to look up the density and molar mass
Post by: Rhodium on June 08, 2004, 06:30:00 PM

Molarity = Moles/dm³
Density = Grams/dm³
Molar mass = Grams/Mole

Molarity = molar mass/density

Title: calculations
Post by: carbocation on June 08, 2004, 06:38:00 PM

okay, the relative molecular weight (M/R) of benzene= 78. Therefore 78g= 1 mole
A 1M benzene solution= 78g benzene per dm3.
The density of benzene= 0.8765 g/cm3.
1 dm3 benzene= 876.5 g.
in 1dm3 pure benzene there is 11.23 moles (876.5/78). Therefore the molarity of 100% benzene= 11.23 moles/dm3

Title: thnk u very much ppl now swim will be able to...
Post by: pink_dust_angel on June 08, 2004, 07:16:00 PM

thnk u very much ppl now swim will be able to dream his dream
;D