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Lena772
 one year ago
An aqueous salt solution is formed by adding 11.67 g sodium sulfate (solute) to water (solvent). What mass (in g) of water is used if the freezing point of the solution is 12.9 oF.
Kf H2O = 1.86 oC/m
When Determining The molality Of The Dissolved Particles, Assume Complete Ionization Of Ionic Compounds  1 Molecule Can Form 1, 2, 3, Or More Dissolved Particles.
Lena772
 one year ago
An aqueous salt solution is formed by adding 11.67 g sodium sulfate (solute) to water (solvent). What mass (in g) of water is used if the freezing point of the solution is 12.9 oF. Kf H2O = 1.86 oC/m When Determining The molality Of The Dissolved Particles, Assume Complete Ionization Of Ionic Compounds  1 Molecule Can Form 1, 2, 3, Or More Dissolved Particles.

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Lena772
 one year ago
Best ResponseYou've already chosen the best response.0I got 64 g and it was wrong. I used the delta T = Kfmolal formula and rearranged it to find that kg solv = (Kf)(Moles solute)/delta T

Lena772
 one year ago
Best ResponseYou've already chosen the best response.0Then I figured out moles of solute, mol pieces and the change in temperature. The Kf was given. However, I feel my delta T may have been incorrect.

Lena772
 one year ago
Best ResponseYou've already chosen the best response.0I got 7.1667 C for delta T. I calculated that their was 0.0822 mol of solute and multiplied this by 3 mol pieces to get my moles of solute. Which made that value 0.2466.

taramgrant0543664
 one year ago
Best ResponseYou've already chosen the best response.2dT=iKfm dT is the change in temperature (TfinalTinitial) i is the van't Hoff disassociation constant Kf would be the 1.86 m is moles of solute divided by kg of solvent

Lena772
 one year ago
Best ResponseYou've already chosen the best response.0It's sodium sulfate not sodium nitrate @Photon336 Na2SO4 > 2 Na+ + SO4 2

Lena772
 one year ago
Best ResponseYou've already chosen the best response.0I understand all that @taramgrant0543664 . I just don't know where I went wrong in my individually calculations or rearranging?

taramgrant0543664
 one year ago
Best ResponseYou've already chosen the best response.2How did you find that temperature?

Lena772
 one year ago
Best ResponseYou've already chosen the best response.0I converted Fahrenheit to Celsius. I got that 12.9 o F = 24 o C and then I converted 0F to Celsius and that gave me like 17C so i found the delta T of that change in C and it ws like the 7.1667 C value.

taramgrant0543664
 one year ago
Best ResponseYou've already chosen the best response.2Which one is initial and final because you could have possibly put them the wrong way which would change the answer

Lena772
 one year ago
Best ResponseYou've already chosen the best response.0Should it have been 32 + 12.9 = 19.1 C because the degree value for both F and C are the same?

Lena772
 one year ago
Best ResponseYou've already chosen the best response.0Initial had to be 32F cause that's the freezing pt of water, but when the solution was added it went to 12.9

Photon336
 one year ago
Best ResponseYou've already chosen the best response.1Forget I said that, your math is correct. \[\Delta T = iK _{b}m \] \[\frac{ \Delta T }{ iK _{b} } = moles/kg \] \[\frac{ moles*i*Kb}{ \Delta T } = kg \] I think here is your formula. (°F  32) x 5/9 = °C

taramgrant0543664
 one year ago
Best ResponseYou've already chosen the best response.2So it should be 12.9(32) so 12.9+32 as final temperature minus initial temperature

Lena772
 one year ago
Best ResponseYou've already chosen the best response.0@Photon would it be 24.0 g?

Lena772
 one year ago
Best ResponseYou've already chosen the best response.0Cause that equals 19.1 @taramgrant0543664 .

taramgrant0543664
 one year ago
Best ResponseYou've already chosen the best response.2And if you put that in to the equation do you get that same number that you already tried?

Photon336
 one year ago
Best ResponseYou've already chosen the best response.1according to wikipedia the freezing point of water is 32 degrees F So originally we had Tf as 12.9 F right? (12.932)*(5/9) = C 32F = Temperature 1 = 0C 24 = Temperature 2 tf i think both have to be in celsius: so T1 = 0 degrees celsius (T2T1) = (240) Celcius 24 celcius

Photon336
 one year ago
Best ResponseYou've already chosen the best response.1but My assumption is that our final answer that the freezing point had to be 0 Degrees C and i converted that 12.9 F right? to Celsius as Temp final

taramgrant0543664
 one year ago
Best ResponseYou've already chosen the best response.2The change in temperature in celsius would be different in F then it is in C so you would have to convert before hand

Lena772
 one year ago
Best ResponseYou've already chosen the best response.0With that value I get 19.1 g, but if I use 19.1 as the change in temp I get 24 g solv.

Lena772
 one year ago
Best ResponseYou've already chosen the best response.0do you guys get 19.1 when you calculate with that value?

Photon336
 one year ago
Best ResponseYou've already chosen the best response.1Tara what did you get for this? \[11.67 grams /142 grams/mol = 0.82 moles \] \[\frac{ 0.82*3*1.86 }{24 } = 0.191 kg \]

Photon336
 one year ago
Best ResponseYou've already chosen the best response.1one question though that Kf shouldn't that be negative as well?

taramgrant0543664
 one year ago
Best ResponseYou've already chosen the best response.2I got 0.019 Your moles @Photon336 I think you're missing a 0 in there

taramgrant0543664
 one year ago
Best ResponseYou've already chosen the best response.2I honestly can't remember the rule when Kf is negative or not it's been a little bit since I've had to do these questions let me see if I can find that rule

taramgrant0543664
 one year ago
Best ResponseYou've already chosen the best response.2It would have been stated if it was negative but water always has a Kf that is 1.86

Lena772
 one year ago
Best ResponseYou've already chosen the best response.0kg to g would be 19.1 though right?

Lena772
 one year ago
Best ResponseYou've already chosen the best response.0It says I have a rounding error of less than 10%. Should I try 19.0 or 19.2?

taramgrant0543664
 one year ago
Best ResponseYou've already chosen the best response.2For me it comes out as 19.065 and 10% is +/0.1 so you could try 19.2 if you want, I'm getting an answer of 19.065 so I would think it would be 19.1 when rounding

Lena772
 one year ago
Best ResponseYou've already chosen the best response.0Well 12.9 F = 24.9444 and we used 24, so that may be the problem. When I calculate with that value I get 18.4 g

Lena772
 one year ago
Best ResponseYou've already chosen the best response.018.4 was correct! Hooray :)

taramgrant0543664
 one year ago
Best ResponseYou've already chosen the best response.2Ya that could be a problem, I never went back and checked the conversion but that could effect it for sure
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