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Freeing point depression

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The purpose of lab this week is to do "comfirmatory experiments" that further explore the properties of your unknown compound and confirm that it reacts appropriately for the compound you predicted it to be at the end of lab last week.

1. Suppose your unknown is sodium acetate. When a solution of calcium chloride is added to your unknown what will happen?

A. A white precipitate of sodium chloride forms

B. No precipitate forms

C. Gaseous HCl bubbles out

D. A white precipitate of calcium chloride forms

2. If you choose to measure the freezing point of a solution of your compound, what would be the objective of the experiment?

A. To measure the freezing point of the solution

B. To determine the density of the unknown

C. To determine the freezing point of the unknown

D. To determine the molar mass of the unknown

3. Which experiment is not possible to do this week in lab?

A. Reaction prediction tests

B. X-ray diffraction

C. Solubility tests

D. Freezing point depression

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Two problems that involve calculating the value of a freezing point and to prove a statement about A statistical thermodynamic model of binary solutions.

1. If the vapor pressures of the two components in a binary solution are grven by
P1 = x1*P1*e^(u(x2^2))/RT and P2 = x2*P2*e^(u(x1^2))/RT
Show that,
Del(mix)*G/u = Del(mix)*G/(n1+n2)u = (RT/u) * (x1 ln(x1) * x2ln(x2))*x1x2
Del(mix)*S/R = Del(mix)*S/(n1+n2)R= -(x1 ln(x1) * x2ln(x2))
Del(mix)*H/u = Del(mix)*H/(n1+n2) = x1x2

A solution that satisfies these equations is called a regular solution. A statistical thermodynamic model of binary solutions shows that u is proportional to 2E12 - E11 -E22 ,where, Eij is the interaction energy between molecules of components i and j. Note-that u = 0 if E12 = (E11+ E22)/2, which means that energetically, moiecules of components 1 and 2 *like" the opposite molecules as well as their own.

2. Calculate the value of the freezing point depression constant for nitro-benzene, whose freezing point is 57 degree centigrade and whose enthalpy of fusion is 11.59 kJ/mol


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