CHEM IA : Freezing Point of Ice

[saranordin869]

Hi there!

I want to ask your opinion regarding my IA Chemistry. My RQ is   "Does different type of salt, Nacl, MgCl2, CaCl2, KCl and C2H3NaO2 affects the freezing point of ice by determining the change in temperature using equal amount of salt?"  . 

My 1st issue is : When I analyse the result, I can only produce bar graph since I am using TYPE of salt. My teacher is worried because she said bar graph is not good enough. But I dont understand why it is not good enough..but whatever it becomes a problem to me now. 

2nd issue : My calculations is very little which is only to calculate change in temperature..Do you have any idea how I can elaborate on calculations like maybe I should look at enthalphy or something? My result would be the initial and final temperature of the ice.

PLEASE HELP ME I REALLY AM LOST. GOD BLESS YOU GUYS! 

[bguloglu]

Well you could extend the investigation by looking at freezing points for each salt over a RANGE of concentrations. The problem is that theoretically, the investigation shouldn't yield different results for different salts (provided that the concentration of ions in the solutions are equal) since colligative properties are an extension of a concept called chemical potential in thermodynamics, and do not depend on the nature of the solute.

[saranordin869]

33 minutes ago, bguloglu said:

Well you could extend the investigation by looking at freezing points for each salt over a RANGE of concentrations. The problem is that theoretically, the investigation shouldn't yield different results for different salts (provided that the concentration of ions in the solutions are equal) since colligative properties are an extension of a concept called chemical potential in thermodynamics, and do not depend on the nature of the solute.

You are suggesting to use different mass of salt is it? Ive think of this but i dont think it is an exploration because logically, higher mass of salt results in lower freezing point of ice. Different salts doesnt give different effect? But my results says otherwise..or is it bcos the concentration isnt the same?? 

[kw0573]

Colligative properties are based on ideal solutions. Since you are working with real solutions (where particle size and IMF are not neglibigle) you need to correction factors for each compound. If you look for calculations or ideal solutions, they don't use mass but rather molality (mol salt / kg water). What @bguloglu said was to use different molalities or concentrations, for each type of salt. There are inherently less calculations you can do using bar graphs. You can try quantifying the data using molality or if you like, mass. 

[saranordin869]

5 hours ago, kw0573 said:

Colligative properties are based on ideal solutions. Since you are working with real solutions (where particle size and IMF are not neglibigle) you need to correction factors for each compound. If you look for calculations or ideal solutions, they don't use mass but rather molality (mol salt / kg water). What @bguloglu said was to use different molalities or concentrations, for each type of salt. There are inherently less calculations you can do using bar graphs. You can try quantifying the data using molality or if you like, mass. 

Okay I understand that you guys are suggesting to use different concentrations of salt. BUT, I dont think I am doing any exploration by varying the mass because logically we know that when the amount of salt increase, the freezing point of ice must decrease as well. So, there is no exploration right?

[bguloglu]

Yes, but a qualitative judgement call based on predictions is not the same as being able to work out the mathematical relationship between the two variables using data you have collected. Remember, the IB does not want you to write a doctorate dissertation and discover sth new, it just wants you to explore a topic further. At least for the syllabus that they had when I took the exams, if it's changed, it might of course be different.