gchem questions

[baedero1]

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#1. a 0.60M solutions is made by dissolving soild compound X in water, after ten seconds, the concentration of X is 0.40M all of the following could account for these results EXCEPT one. which one is this exception?
a. precipitation
b. neutralization
c. evaporation
d. decomposition
e. disproportionation

the answer is a

#2. CCl4 is observed to have higher b.p. than CHCl3. all of the following statements are true based on this observation EXCEPT one. which one is this exception?
a. dispersion forces are experienced by CCl4 than CHCl3
b. at a given temp, the vapor pressure of CCl4 is less than that of CHCl3
c. the molar heat of vaporization of CCl4 is greater than that of CHCl3
d. dipole-dipole interations are responsible for the larger b.p. of CCl4.

the answer is d

Can any1 explain these questions?

 

[happyasaclam88]

i don't understand number 1, but for number 2 d makes sense since ccl4 isn't a polar molecule. the 4 cl's in tetrahedral positions so there's no net dipole moment.

 

[bergoshe]

#1. a 0.60M solutions is made by dissolving soild compound X in water, after ten seconds, the concentration of X is 0.40M all of the following could account for these results EXCEPT one. which one is this exception?
a. precipitation
b. neutralization
c. evaporation
d. decomposition
e. disproportionation

the answer is a

Can any1 explain these questions?

If it were to precipitate, then it would not have dissolved in the first place. I honestly don't really understand how the answer could not be C as well though... Definitely a toughie.

 

[doc3232]

#1. a 0.60M solutions is made by dissolving soild compound X in water, after ten seconds, the concentration of X is 0.40M all of the following could account for these results EXCEPT one. which one is this exception?
a. precipitation
b. neutralization
c. evaporation
d. decomposition
e. disproportionation

the answer is a

#2. CCl4 is observed to have higher b.p. than CHCl3. all of the following statements are true based on this observation EXCEPT one. which one is this exception?
a. dispersion forces are experienced by CCl4 than CHCl3
b. at a given temp, the vapor pressure of CCl4 is less than that of CHCl3
c. the molar heat of vaporization of CCl4 is greater than that of CHCl3
d. dipole-dipole interations are responsible for the larger b.p. of CCl4.

the answer is d

Can any1 explain these questions?

How can CCl4 have dipole dipole? I don't think it can. Something like HCl can because it has different electronegative atoms. All the Cls have the same affect so it won't have them.
CClH3 can though, it has H's and Cl's.
Hope this helped.

 

[smile101]

1) I don't know why the answer would't be C because the water will evaporate not the solid, which should increase the conc of solution. I understand ppt part because when a solid ppt I>Ksp, which means more solid is present...a supersaturated solution...which should actually have higher conc than original...please correct me if I am wrong.

2) a is right because CCl4 is non-polar and will have dispersion forces (I don't think this is the sole reason for high BP)
b is right because high BP means lower vapor pressure
c is right because high BP means higher heat of vaporization
d is wrong because dipoles exist only if you have polar molecules. CCl4 is nonpolar tetrahedral (CHCl3 is polar though tetrahedral), so only weak dipsersion forces exist. I do think that high MW contributed much to that high BP although its not one of the answer choices.

Where did you get these questions from????
Do they have explanations???