Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Fish200398 on November 15, 2019, 04:22:08 AM
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1 g each of these dissolve in 1 L water
1. Glucose
2. Sodium chloride
3. Sodium sulfate
4. Magnesium chloride
My answer :
Glucose is the lowest, due to covalent bonding with no hydrogen forces not ionic
Na2so4 Nacl and mgcl2
But what about these 3?
Should i count it wih formula of t=i*kb*b
b = molality
Kb = constanta
i = van hoff factor
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Should i count it wih formula of t=i*kb*b
Yes. Same for glucose - ionic vs. covalent is irrelevant - and it does have hydrogen bonding.
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according to your formula t/kb=i*b should show the highest value. Compare all i*b values.
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After i calculated, i get nacl = 0.035, and mgcl2 = 0.0315, so highest is nacl
But the answer isnt nacl, why?
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From the question:
"Order the one has the highest boiling point to lowest"
I understand that the answer should be:
eg.) 1>3>2>4 or 1,3,2,4
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Tell me how to conclude that?
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Order - the highest boiling point - to lowest
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Tell me how do i decide which one is higher and lower?
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You were on the right lines before. @AWK is simply pointing out that the question doesn't say "which is highest?" but "put them in order".
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Ok. But the highest isnt nacl, why is it wrong then?
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From my calculation nacl is bigger than mgcl2, but why the answer mgcl2 has higher boil point than nacl?
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Must be an error, I got the same numbers as you did for NaCl and MgCl2 and your conclusion that NaCl has the highest boiling point looks OK.
Technically i for MgCl2 will be lower than 3 due to the ion association, whether you should account for that or nor depends on the course level. If that is a HS course i=3 is a reasonable first approximation.
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Really? Thanks borek and all
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Four months ago there was an analogous question (using 10 g of substances) with the same wrong answer: magnesium chloride
https://chemistry.stackexchange.com/questions/118229/which-one-has-the-highest-boiling-point
Please, give the source of your problem
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Yes. I found it but i already posted here. What do i do by "give source of problem"
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AWK asks where did you got the problem from - was it in a book, or asked by a teacher? found in some internet source?
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I got the question from pdf in internet
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Can you give this link?
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Yes. https://www.google.co.id/amp/s/onmyrandommind.wordpress.com/2016/09/18/soal-s1/amp/ chemistry year 2013
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You changed question and numbers - but this is not fatal.
There is an evident error in the problem (7 fields for answers instead of 4) also - non-fatal.
And there is the error in the answer (I suppose this is the printing error) - but fatal.
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Yes. What is the evident error in the problem 7? Is it only the answer that wrong?
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The answer should be 2
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I see. Thanks awk
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Actually that's not the only problem with these questions. Problem 6 has no answer, as none of the underlined elements gets oxidized. The only equation that seems to be suggesting oxidation is 3, but it is not a redox, just a simple metathesis.
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There is an evident error in the problem (7 fields for answers instead of 4) also - non-fatal.
No, that's OK, the table is for 7 problems all being part of the set I (which starts on a previous page). And the problem no 7 needs a single answer, as it asks only "which has the highest".
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Yes borek. The 1-7 table is for all questions of set I. And for no 6 in set I, yes i kinda find it weird at start, but i guess i had to choose 3.
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There is no good answer to problem 6 from Part I. Reaction 3 is not a redox reaction as Borek pointed out.
Moreover, at least organic problems VI and VII are partially questionable.
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Why its questionable?
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Part VI. Compound D should be salicylic acid, compound E - phenol
Part VII. Reaction 1 - when not stated reaction undergoes at room temperature - this reaction needs over 300°C
Reaction 3 - ethanol at 160°C without catalyst = ethanol vapors.
With catalyst - ethene (ethylene)
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Ok. Thanks awk. Guess in other questions (other year) might be mistakes too
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It's a waste of time looking for them unless someone falls into the trap again.
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Yes