aommaster Posted October 29, 2005 Posted October 29, 2005 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!
RyanJ Posted October 29, 2005 Posted October 29, 2005 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
aommaster Posted October 29, 2005 Author Posted October 29, 2005 So basically, if the solution is saturated, it would that the lowest possible solubility?
RyanJ Posted October 29, 2005 Posted October 29, 2005 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
aommaster Posted October 29, 2005 Author Posted October 29, 2005 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!
RyanJ Posted October 29, 2005 Posted October 29, 2005 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 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 Cheers, Ryan Jones
woelen Posted October 29, 2005 Posted October 29, 2005 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.
aommaster Posted October 29, 2005 Author Posted October 29, 2005 Thanks alot for clearing that up woelen! Ryan:I guess to test this, 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 Thanks alot for your help guys!
RyanJ Posted October 29, 2005 Posted October 29, 2005 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
RyanJ Posted October 29, 2005 Posted October 29, 2005 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
aommaster Posted October 29, 2005 Author Posted October 29, 2005 Don't worry, I'll ask my lab technician. She'll probably know what it is
RyanJ Posted October 29, 2005 Posted October 29, 2005 Don't worry, I'll ask my lab technician. She'll probably know what it is Yea she should do - I'll ask mine too on monday (If they don't know then I'll ask them why not ) Cheers, Ryan Jones
aommaster Posted October 29, 2005 Author Posted October 29, 2005 I did a quick search in google, is this what you are talking about? http://humboldt.edu/~scimus/Instruments/Therm-Edser/BckmnFPapp.htm http://www.koehlerinstrument.com/products/K29750.html
RyanJ Posted October 29, 2005 Posted October 29, 2005 I've seen the second one before but nope none of those are the one. The one I am refering to is basically a coil just there is something different about it Cheers, Ryan Jones
aommaster Posted October 29, 2005 Author Posted October 29, 2005 No problem, they looked like what you were describing. Anyway, I'll ask the lab technician about it We'll see who gets the answer first
jdurg Posted October 30, 2005 Posted October 30, 2005 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).
Borek Posted October 30, 2005 Posted October 30, 2005 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
aommaster Posted October 31, 2005 Author Posted October 31, 2005 Wow! Thanks alot for that guys! Ryan: I asked my lab technician about it, but she says that they just call it the freezing point aparatus. My chemistry teacher said the same thing, they had no special name for it
RyanJ Posted October 31, 2005 Posted October 31, 2005 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
aommaster Posted October 31, 2005 Author Posted October 31, 2005 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
RyanJ Posted October 31, 2005 Posted October 31, 2005 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
aommaster Posted October 31, 2005 Author Posted October 31, 2005 No problem. From now on, we'll just call it the "freezing point apparatus"
Borek Posted November 1, 2005 Posted November 1, 2005 RyanJ: freezing point is pressure dependent (sometimes more, sometimes less, depends on the substance), so in case of water under high pressure it will be not overcooling, but a real change. Best, Borek -- Chemical calculators at www.chembuddy.com pH calculator concentration conversion
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