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Topic: 2 solutions mixed  (Read 532 times)

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Offline Helly

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2 solutions mixed
« 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

Offline mjc123

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Re: 2 solutions mixed
« Reply #1 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?

Offline Helly

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Re: 2 solutions mixed
« Reply #2 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

Offline mjc123

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Re: 2 solutions mixed
« Reply #3 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.)

Offline MNIO

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Re: 2 solutions mixed
« Reply #4 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.

Offline Helly

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Re: 2 solutions mixed
« Reply #5 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?

Offline AWK

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Re: 2 solutions mixed
« Reply #6 on: March 11, 2020, 01:02:55 PM »
Probably problem concern the elevation of  boiling point and the depression of freezing point after mixing.
AWK

Offline alfred0809

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Re: 2 solutions mixed
« Reply #7 on: March 12, 2020, 01:48:51 AM »
What are some colorless/clear solutions that when mixed will precipitate into something colourful that primary school students would enjoy.

Offline mjc123

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Re: 2 solutions mixed
« Reply #8 on: March 12, 2020, 06:35:00 AM »
If you've got a new question, start a new thread, don't hijack someone else's.

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