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Chemistry Help

us3rnotfound

Diamond Member
Jun 7, 2003
5,333
3
81
I need help on how to solve this problem


An automobile antifreeze mixture is made by mixing equal volumes of ethylene glycol (d = 1.114 g/mL; 62.07 g/mol) and water (d = 1.00 g/mL) at 20 oC. The density of the mixture is 1.070 g/mL. Express the concentration of ethylene glycol as molarity.


Thanks
 

Ika

Lifer
Mar 22, 2006
14,267
3
81
Not 100% sure this will work, because I already forgot all my chemistry, but it seems right.

Since you're given both densities of EG and water, and the density of the final mixture, you should be able to figure out the densities of EG and water in the mixture as a percentage. Once you know this, assign a random number to total liters, such as 10. Figure out the liters of EG from the percentage you got, get the mass from the density, and ... profit?
 

newb111

Diamond Member
Oct 8, 2003
6,992
1
81
Originally posted by: us3rnotfound
Originally posted by: newb111
8.97 M
Yeah, I got that, but it grades it as incorrect.

This is an online assignment BTW.
Actually due to significant digits (4) the answer is 8.974. Have you tried that one?
 

stankonia3000

Member
Mar 2, 2001
62
0
0
yeah molarity is moles/liter

here's what i did:

lets say i add 500mL ethylene glycol to 500mL water (equal volumes like the problem says)

how many moles is that?

500mL X 1.114g/mL x 1mol/62.07g = 8.97 mol in that 500mL but there are 1000 mL in total volume of my solution and 1000mL is 1 Liter (remember molarity is moles/liter) so how many moles in one liter???

8.97mol/500mL * 1000mL/1L = 17.94mol/L

i could be wrong though b/c its been like 7 years since i took that class and i am drunk right now
 

newb111

Diamond Member
Oct 8, 2003
6,992
1
81
Originally posted by: stankonia3000
yeah molarity is moles/liter

here's what i did:

lets say i add 500mL ethylene glycol to 500mL water (equal volumes like the problem says)

how many moles is that?

500mL X 1.114g/mL x 1mol/62.07g = 8.97 mol in that 500mL but there are 1000 mL in total volume of my solution and 1000mL is 1 Liter (remember molarity is moles/liter) so how many moles in one liter???

8.97mol/500mL * 1000mL/1L = 17.94mol/L

i could be wrong though b/c its been like 7 years since i took that class and i am drunk right now


You were on the right track, however the 8.97 mol is only in the ethanol solution, not in the water. So when you add water you still have the same number of mol, just greater volume, so you have 8.97mol/1L.
 

stankonia3000

Member
Mar 2, 2001
62
0
0
yeah now that i think about it youre right....i shouldnt have multipled by 2 b/c the numbers of moles of ethylene glycol stays constant when i bulk up to 1L solution...dont know why its saying your wrong dude b/c 8.97 is right...sorry
 

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