Google Answers Logo
View Question
 
Q: chemistry ( Answered 5 out of 5 stars,   0 Comments )
Question  
Subject: chemistry
Category: Science > Chemistry
Asked by: teatea-ga
List Price: $2.00
Posted: 06 Jul 2003 16:38 PDT
Expires: 05 Aug 2003 16:38 PDT
Question ID: 225833
The boiling point of a solution containing 20.0g C12H22O11 in 500.0g H2O is:
a. 100.037 degrees C
b. 100.060   "
c. 101.735   "
d.  10.468   "
Answer  
Subject: Re: chemistry
Answered By: livioflores-ga on 06 Jul 2003 18:15 PDT
Rated:5 out of 5 stars
 
I am here again teatea!!!

Some concepts:
The temperature at which the vapor pressure of the liquid is equal to
the atmospheric pressure is termed as the boiling point.
The boiling point of any liquid increases by adding a non-volatile
solute to it. This increases the vapor pressure.
Elevation in the boiling point ( DTb ) is directly proportional to the
amount of solute present.
Concentration of the solute is expressed in molalities (m) 
(molality = moles of solute / kilograms of solvent) 

DTb = m.Kb 
where
m = concentration in molalities 
Kb = molal boiling point elevation constant; for the water Kb = 0.512
ºC/mol.
Boiling point of the water is 100ºC.

Now we can solve the problem.

First of all we need to calculate how many moles of the solute we
have:
1 mole C12H22O11 = 12x12g + 22x1g + 11x16g = 342 grams.
We have 20g of C12H22O11 in the solution, that are 20g/342g = 0.058478
moles.

Now we can calculate the molality m:
m = moles of solute / kilograms of solvent = 
  = 0.058478 moles / 0.5 kg = 0.116956

Then the elevation in the boiling point ( DTb ) is:
DTb = m.Kb = 0.116956 x 0.512 = 0.06 ºC

The boiling point of the solution is:
SolTb = 100ºC + 0.06ºC = 100.06 ºC.

The correct answer is b.

Hope this helps.

Regards.
livioflores-ga
teatea-ga rated this answer:5 out of 5 stars

Comments  
There are no comments at this time.

Important Disclaimer: Answers and comments provided on Google Answers are general information, and are not intended to substitute for informed professional medical, psychiatric, psychological, tax, legal, investment, accounting, or other professional advice. Google does not endorse, and expressly disclaims liability for any product, manufacturer, distributor, service or service provider mentioned or any opinion expressed in answers or comments. Please read carefully the Google Answers Terms of Service.

If you feel that you have found inappropriate content, please let us know by emailing us at answers-support@google.com with the question ID listed above. Thank you.
Search Google Answers for
Google Answers  


Google Home - Answers FAQ - Terms of Service - Privacy Policy