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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: aaronhkg on March 03, 2011, 12:29:42 PM

Title: Reason of anomaly between calculated value of Kb and actual Kb
Post by: aaronhkg on March 03, 2011, 12:29:42 PM

There is a question in my coursework:

0.76g of substance of R.M.M. = 132 is dissolved in 27g of water and raises its boiling point by 0.333oC. Calculate the apparent boiling-point constant for water and compare it with the actual value of 0.52 K mol-1 1000g-1. Explain this anomaly.

Here is my working,

n=0.76/132 = 5.758X10-3 mol of substance

5.758X10-3 mol of substance = 0.027Kg H2O X m/Kg H2O

X = 0.213m

then,

let kb as Y,

0.333/Y=0.213m, Y = 1.562.

1.562 compares to 0.52 which is 3 times larger than the actual value, how to explain this anomaly?

Thanks

Title: Re: Reason of anomaly between calculated value of Kb and actual Kb
Post by: Borek on March 03, 2011, 12:58:23 PM

Quote from: aaronhkg on March 03, 2011, 12:29:42 PM

Y = 1.562.

1.562 of what?

Title: Re: Reason of anomaly between calculated value of Kb and actual Kb
Post by: aaronhkg on March 03, 2011, 01:49:26 PM

Y is the calculated Kb for H2O, where the actual Kb for H2O is 0.52.

Title: Re: Reason of anomaly between calculated value of Kb and actual Kb
Post by: rabolisk on March 03, 2011, 03:12:22 PM

Boiling point elevation is dependent on number of particles in solution.