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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Fish200398 on February 11, 2020, 11:33:21 AM

Title: 2 solutions mixed
Post by: Fish200398 on February 11, 2020, 11:33:21 AM

3.6 gram glucose in 500 gram water mixed with 4.75 gram MgCl2 in 1000 gram water. (Kd = 0.52 °C/m. and Kf = 1.86 °C/m.) whats the temperature after mixing?

i think that the glucose solution will increased in temperature and the MgCl2 solution will decrease in temperature, until they both reached equilibrium temperature.
Q = mcΔT
m = molal
but i dont know how to find ΔT

Title: Re: 2 solutions mixed
Post by: mjc123 on February 11, 2020, 12:45:08 PM

What's the temperature before mixing? Without knowing that you're stuck. Are they at different temperatures before mixing?

Why do you quote Kd and Kf? Are they relevant? (Does the question give you them as red herrings?)

m means molal in Kd = 0.52°C/m, but it does not mean molal in Q = mcΔT. What does it mean?

There is not enough information to answer the question. Can you quote the whole question?

Title: Re: 2 solutions mixed
Post by: Fish200398 on February 11, 2020, 12:56:38 PM

Thats the all information.. yes i think i need the early temperature..
Delta T = kb molal i
Or delta T = kf . Molal . I

Title: Re: 2 solutions mixed
Post by: mjc123 on February 12, 2020, 04:37:28 AM

Quote

Delta T = kb molal i
Or delta T = kf . Molal . I

That's irrelevant unless you're considering the change in the melting or boiling point. What you're asking for is the temperature change on mixing - something quite different. (And still without enough information to determine it.)

Title: Re: 2 solutions mixed
Post by: MNIO on February 12, 2020, 04:59:16 PM

can you copy and paste the exact problem?  here's why I ask
  dTfp = Kf * m * i  is an estimate of FREEZING POINT of solutions
  dTbp = Kb * m * i is an estimate of BOILING POINT of solutions

where i is related to the formula of the salts
m is related to the mass of salts AND mass of H2O

essentially you're given the information you need to calculate fp and bp of the resulting solutions

************
the way you asked the question "what is the TEMPERATURE after mixing" is a different problem entirely and is way beyond the scope of a high school chemistry homework problem.

Title: Re: 2 solutions mixed
Post by: Fish200398 on March 11, 2020, 12:35:48 PM

The question was

 3.6 gram glucose in 500 gram water mixed with 4.75 gram MgCl2 in 1000 gram water. (Kd = 0.52 °C/m. and Kf = 1.86 °C/m.) whats the temperature after mixing?

What formula do i use? What information was lacking?

Title: Re: 2 solutions mixed
Post by: AWK on March 11, 2020, 01:02:55 PM

Probably problem concern the elevation of  boiling point and the depression of freezing point after mixing.