OC question and GC question

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1. how many structural isomers with the formula C3H6 will react with hydrogen in the presence of a nickel catalyst to form propane?
answer is 2.

2. in general, how will the solubility of a gas in a liquid be affected by a decrease in temperature?
solubility will increase

can someone explain these two for me ? thanks

 

[DrTacoElf]

2. in general, how will the solubility of a gas in a liquid be affected by a decrease in temperature?
solubility will increase

less kinetic energy therefore the gas will be less volatile would be my argument.

 

[sinned]

for number 1 the index of hydrogen deficiency is 1, meaning there is one double bond, and within 3 carbons the structure can only be propene, and for propene the double bond can be only at TWO places which will form propane after hydrogen with nickel catalyst.

for number 2 the solubility increases with decrease in temperature because at higher temperatures, more of the liquid turns into vapor, leaving the liquid phase, so less is in solution, but if you decrease temperature, there is less vapor and more of it stays in the liquid phase, thus solubility is increased.

 

[drat]

Think of the gas phase solubility in terms of a can of pop (or soda). We keep pop cold in order to prevent it from going flat -- when it goes flat it's because there is less carbon dioxide in solution. Lower the temperature to increase the CO2 solubility so you get nice, fizzy pop!

But we, as future dentists, know, pop is bad for teeth so don't drink it!
drat!

 

[HBomb]

for number 1 the index of hydrogen deficiency is 1, meaning there is one double bond, and within 3 carbons the structure can only be propene, and for propene the double bond can be only at TWO places which will form propane after hydrogen with nickel catalyst.

for number 2 the solubility increases with decrease in temperature because at higher temperatures, more of the liquid turns into vapor, leaving the liquid phase, so less is in solution, but if you decrease temperature, there is less vapor and more of it stays in the liquid phase, thus solubility is increased.

I remember this questions from Kaplan. sinned mentioned the first isomer. The right deduction is one degree of unsaturation, as sinned stated (implied). The other isomer is cyclopropane. I never liked this question, by the way because Kaplan says there's so much ring strain on cyclopropane that it will break into n-propane when hydrogen is around (maybe b/c of H2/Ni, not sure). But how are we to deduce that is will break b/c of ring strain? IMO, on the DAT, we're really responsible for knowing sinned's answer, not this one.

 

[x-linked]

I remember this questions from Kaplan. sinned mentioned the first isomer. The right deduction is one degree of unsaturation, as sinned stated (implied). The other isomer is cyclopropane. I never liked this question, by the way because Kaplan says there's so much ring strain on cyclopropane that it will break into n-propane when hydrogen is around (maybe b/c of H2/Ni, not sure). But how are we to deduce that is will break b/c of ring strain? IMO, on the DAT, we're really responsible for knowing sinned's answer, not this one.

but cyclopropane isnt propane, is it 😕 😕

 

[HBomb]

propene and cyclopropane have the formula C3H6. They are structural isomers.

n-propane is C3H8

So, to answer your previous question cyclopropane isn't propane (n-propane). To answer your original post, the isomers are propene and cyclopropane.

 

[sinned]

exactly what Hbomb said, but this is a bad question and most likely wont be on the DAT...just absorb the concepts but dont expect to see it on the DAT

 

[x-linked]

thank you all ! ! !