(another) chemistry question?

[NubianPrincess]

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If it is given that an aqueous solution of ethylene glycol is 40.0% (CH2OH)2 by mass and has a density of 1.05g/mL, how do you find the molarity and molality?
Any help is appreciated.

 

[jmejia1]

•••quote:•••Originally posted by Nubian:
•If it is given that an aqueous solution of ethylene glycol is 40.0% (CH2OH)2 by mass and has a density of 1.05g/mL, how do you find the molarity and molality?
Any help is appreciated.•••••First you need the definition of molarity and molality.

1.) Molarity is moles of ethylene per liter of solution.
2.) Molality is moles of ethylene per Kg of solution

One liter of the solution wieghts: (1.05g/ml*1000ml/L) = 1050 grams

40% of this total weight comes from ethylene glycol: (1050grams*0.40) = 420 grams of ethylene per Liter.

Molecular weight of ethylene glycol is 62g/mol. Therefore: ((1mole/62grams)*420grams) = 6.77 moles/liter = molarity

Maybe someone can field the Molality one and or confirm the molarity answer.

 

[Tobtolip]

•••quote:•••.) Molaity is Kg of ethylene per liter of solution
••••Thought molality was Moles of Solute/Kilograms of Solvent

 

[jmejia1]

•••quote:•••Originally posted by Tobtolip:
• •••quote:•••.) Molaity is Kg of ethylene per liter of solution
••••Thought molality was Moles of Solute/Kilograms of Solvent•••••You're right. Sorry about that. I'll edit for correction.

 

[Sm00th13]

Actually, the definition of Molality is:

A concentration unit equal to the number of moles of solute per kilogram of SOLVENT. I'm not sure the answer for Molality is correct.

 

[NubianPrincess]

Thanks for the help. So let me get this straight, this solution will always have 450g of ethylene glycol, and I can find the molality from the number of moles...would the kg of solvent be 1050g-420g?
If I wanted to find the mole fraction of ethylene glycol, would that be the moles of ethylene glycol divided by what since I don't know what the rest of the solution is made up of?

 

[bigfkd22]

If its in a (ag) solution the solvent is H20. The 60% is H20. Find moles using method from above.