Jump to content

Solubility


aommaster

Recommended Posts

Hi guys!

 

Consider the following situation:

You have 5 beakers with different salt concentration solutions:

Beaker 1: 0%

Beaker 2: 5%

Beaker 3: 10%

Beaker 4: 15%

Beaker 5: 20%

 

Which one would have the lowest freezing point? My guess would be the 20% one.

 

Also, is there a limit to how low the freezing point can go? Does that limit mean that no matter how much of the solute you add, the freezing point won't reduce any further?

 

Thanks alot guys!

Link to comment
Share on other sites

Hi guys!

 

Consider the following situation:

You have 5 beakers with different salt concentration solutions:

Beaker 1: 0%

Beaker 2: 5%

Beaker 3: 10%

Beaker 4: 15%

Beaker 5: 20%

 

Which one would have the lowest freezing point? My guess would be the 20% one.

 

Also' date=' is there a limit to how low the freezing point can go? Does that limit mean that no matter how much of the solute you add, the freezing point won't reduce any further?

 

Thanks alot guys![/quote']

 

I'd also say that the 20% one would have the lowest freezing point.

 

As for the limit I think thelimit is related to the maximum solubility. You may also be interested to know that really and I mean really pure water has a freezing point below 0 degrees Centrigrade becase the water crystals don't have any impurities to form crystalls arround - its pretty neat!

 

Cheers,

 

Ryan Jones

Link to comment
Share on other sites

So basically, if the solution is saturated, it would that the lowest possible solubility?

 

If I get what your saying there then yes when that solute's solution is saturated (If you wanted to add another one then its more complex) then its solubility in that solution would be zero because no more can dissolve. Note: I said in that solution not in an solution ;)

 

Or did you mean the freezing point there? If so then once the solution is saturated it will have the lowest possible freezing point for that solvant. If on the other hand you has something that was more soluable then you could make the freezing point even lower :)

 

Do an experiment to test it out is what I would reccomend :)

 

Cheers,

 

Ryan Jones

Link to comment
Share on other sites

No problem! Thanks alot for that! Would sugar and salt work out as a good experiment?

 

And how should I measure the freezing point? Would sticking it into a freezer with a thermometer work?

 

Thanks alot for your time Ryan!

 

I'd say sugar and salt would work fine as would anyhting else you can mweigh accuratly and will dissolve :D

 

As for the way to do this a freezer with a thermometer should do the job but if your looking for somehting more technical you could use a water bath with water in it (Who would have guessed ;) then put a beaker with your solution in it (and a themrometer) and then add ammonium nitrate to the water bath and that will cool the temperature of the water bath so you can watch it live :D

 

Cheers,

 

Ryan Jones

Link to comment
Share on other sites

If solubility is limited, then the lowest freezing point may be due to the limit in solute. However, this is not always true. Sometimes a phase-system (keyword: eutectics?) is created which has more complex behavior and has a minimum freezing point.

 

Just consider a mix of water and acetic acid. Pure water freezes at 0 C, pure acetic acid freezes at 16 C. Now imagine that you draw a graph with at the x-axis the percentage acetic acid (which ranges from 0 to 100) and at the y-axis the freezing point.

 

This function will have a minimum, quite below 0 C, at 0% its value equals 0 and at 100% its value equals 16. So, you get a 'parabolic-like' shape of the graph.

 

So, in practice, the situation may be more complex.

Link to comment
Share on other sites

Ryan:I guess to test this' date=' I'll need to use a freezer, since I'm not sure whether my school will allow me to get my hands on ammonium nitrate :)[/quote']

 

Probably although this stuff is safe as long as the people who use it ar I think :)

Its probably better to stick with a freezer anyway but you may want to ask if your school has some other equipment to do this... there is one where a special coil is put arround the beaker and it drains the heat but I'm not shure your school will have something like this either but its worth asking!

 

When I used this stuff it froze my beaker to the table oops... should have gotten the water off these first!

 

Cheers,

 

Ryan Jones

Link to comment
Share on other sites

Thanks alot for that Ryan!

 

No problem - I don't remember the name for the cil apparatus but if I do I'll be shure to tell you :)

 

Like I said there are loads of ways to cool things (You'll definatly want something live so you can mwatch its temperature closly) and I'm shure your school must have oone or more of them :)

 

That device is clever though, the water that goes through there - something happens to it and one lot of it is made boilling hot and the other part goes freezing cold... I wish I could remember what it was called and then I could look up how it worked again ;)

 

Cheers,

 

Ryan Jones

Link to comment
Share on other sites

Remember that freezing point depression is more dependent on the NUMBER of solute particles and less so on what the solute is. If you look at the ability of sodium chloride and calcium chloride to lower the freezing point of water, you'll see that calcium chloride is MUCH more effective because when it dilutes it gives up 3 ions in solution; one calcium and two chlorides. Calcium phosphate is a great freezing point depressant as it donates 5 substances when it dissolves in water.

 

So when looking at which solute would result in a lower freezing point, take a look at the molarity of 'particles' and not the substance. (A one molar solution of sugar would have one mole of particles, while the same in NaCl would have two moles of particles).

Link to comment
Share on other sites

You may also be interested to know that really and I mean really pure water has a freezing point below 0 degrees Centrigrade becase the water crystals don't have any impurities to form crystalls arround - its pretty neat!

 

That's not true.

 

Freezing point of the pure water is exactly 0 deg C. However, if the water is sufficiently pure (it can contain dissolved substances, but no precipitates) it can be brought below zero, it is called overcooling. That's similar to overheating, just in different direction.

 

Best,

Borek

--

Chemical calculators at www.chembuddy.com

pH calculator

concentration conversion

Link to comment
Share on other sites

That's not true.

 

Freezing point of the pure water is exactly 0 deg C. However' date=' if the water is sufficiently pure (it can contain dissolved substances, but no precipitates) it can be brought below zero, it is called overcooling. That's similar to overheating, just in different direction.

[/quote']

 

Oh.. seems I miss read it - you are correct :)

 

You could also do this by using extreme preassures - the waterwould have a hard time freezing then :)

 

@aommaster: Ah right - thanks for the information!

 

Cheers,

 

Ryan Jones

Link to comment
Share on other sites

Are you sure that there was a name for this apparatus? From what the lab technician seems to tell me, there doesn't seem to be a name for it :)

 

I'm shure there was a name for it then again it was about 4 years ago so I don't really know :)

 

Cheers,

 

Ryan jones

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.