Boiling point elevation problem

[orangepopsicle]

Hello,

I was solving a problem for boiling point elevation and one of the answer choices was K2CO2. I was wondering what the "i" for this compound would be. Would it be 3 because CO2 is considered one compound or would each element contribute for a total of an i of 5?

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[orangepopsicle]

Sorry i meant K3CO2

 

[100%permwinner]

You sure this compound exist? I think it should be K2CO3. CO3 is the only polyanion of C and O with a -2 charge. K2CO3 has 2 mol of cation and 1 mol of anion, i = 3.

 

[RuffDay]

An ionic compound will dissociate readily, and this is definitely an ionic compound (metal + nonmetal). This will dissociate into 3 ions (2 cations and 1 anion). Some few things to know is that more ions will increase the boiling point and decrease the freezing point. It depends on the molality of the molecule as well, this is different from osmotic pressure where it depends on the molarity.

 

[orangepopsicle]

No its definitely K3CO2, its choice E on question #4 on test 1 in DATQvault for chemistry. Maybe they wrote down one of the answer choices wrong.

 

[orangepopsicle]

So ruff day youre saying K3CO2 has an i of 6? I'm confused because the answer on DATQvault says

"The solution with the lowest boiling point will be the solution with the smallest number of ions. Solutes will increase the boiling point of a solvent. The degree of increase is dependent on the number of particles.KCl will give only two particles when dissolved, but the other compounds will give between 3 and five particles and will have a greater effect."

so based on their answer technically the i for the compounds can't exceed 5.

This was the entire question in case anyone wants to reference:

2 moles of the following solutes is added to 1L of pure water. Which of the five ensuing solutions would have the lowest boiling point?

a) CaCl2
b) AlCl3
c) KCl
d) FeCl3
e) K3CO2

 

[RuffDay]

Shoot sorry, my bad. I made a typo! I meant there were 3 ions: 2 cations and 1 anion.

 

[orangepopsicle]

How did you get that? Aren't there 3 cations (the 3 K+) and I'm not quite sure how the CO2 would be considered. Either as a whole (CO2) or divided up as 1 C and 2 O's ?

 

[RuffDay]

a) CaCl2 - Will dissociate into 3 solutes (1 Calcium and 2 Chlorines)
b) AlCl3 - Will dissociate into 4 solutes ( 1 Al and 3 Cl)
c) KCl - Will dissociate into 2 solutes ( 1 K and 1 Cl)
d) FeCl3 - Same as B, but Fe
e) K3CO2 - Will dissociate into 4 solutes (3K and 1CO2)

Lowest boiling point = least amount of moles of solutes. Since all are 2 moles. We can now just look at the # of solutes in each answer.