1. You have four related molecules, XA (mw =140), XB (mw = 100), XC (mw = 80) an

Question

1. You have four related molecules, XA (mw =140), XB (mw = 100), XC (mw = 80) and XD (mw = 120). None of the four molecules can hydrogen bond. During the evaporation of XB, |?T| = 7.2oC. During the evaporation of XD, |?T| = 4.7oC. What would be the expected |?T| during the evaporation of XC?

10.1oC
4.7oC
2.5oC
7.2oC

8. The cooling curves for both a pure solvent and a solution made from the pure solvent and an unknown solute are shown above. What is the freezing point depression, ?T, for the solution? Enter your answer as an integer.  oC

9. A solution was prepared by mixing together 7.20 g of a nonelectrolyte solute with 25.0 g of solvent. The freezing point depression, ?T, for the solution was determined to be 7.30 oC. Kf = 5.11 oC/m for the pure solvent. What is the molecular weight (molar mass) of the solute? Enter your answer as a decimal number.  g/mol

12. How many net atoms are in the face-centered cubic unit cell? ("net" means you have taken into account atom sharing between unit cells) Enter your answer as an integer.

15. A solid metal oxide crystallizes in a cubic unit cell. In the unit cell there are metal (M) ions on every corner and in the center of every face. Oxide ions (O) are found in all of the tetrahedral holes. What is the empirical formula of this metal oxide?

MO2
MO3
M2O
MO
M2O3
M3O2

1. You have four related molecules, XA (mw =140), XB (mw = 100), XC (mw = 80) and XD (mw = 120). None of the four molecules can hydrogen bond. During the evaporation of XB, |?T| = 7.2degreeC. During the evaporation of XD, |?T| = 4.7oC. What would be the expected |?T| during the evaporation of XC? Use the information in this figure to answer questions 7 and 8. 7. The cooling curves for both a pure solvent and a solution made from the pure solvent and an unknown solute are shown above. Which cooling curve is for the solution? Curve A Curve B 8. The cooling curves for both a pure solvent and a solution made from the pure solvent and an unknown solute are shown above. What is the freezing point depression, ?T, for the solution? Enter your answer as an integer. degreeC 9. A solution was prepared by mixing together 7.20 g of a nonelectrolyte solute with 25.0 g of solvent. The freezing point depression, ?T, for the solution was determined to be 7.30 degreeC. Kf = 5.11 degreeC/m for the pure solvent. What is the molecular weight (molar mass) of the solute? Enter your answer as a decimal number. g/mol 12. How many net atoms are in the face-centered cubic unit cell? (net means you have taken into account atom sharing between unit cells) Enter your answer as an integer. 15. A solid metal oxide crystallizes in a cubic unit cell. In the unit cell there are metal (M) ions on every corner and in the center of every face. Oxide ions (O) are found in all of the tetrahedral holes. What is the empirical formula of this metal oxide?

Explanation / Answer

Ques1. delta T decreases with increasing molecular weight as given (XC molecular weight = 80 ). Therefore, deltaT for XC would be 10.1C

Ques2. Curve B will be for the solution

Ques3. Fpt. Depression is find out using following equation

T = Kf m. Where: T = change in bpt. or fpt. of the solutioncompared to the pure solvent. Kf = freezing point depression constant for the solvent

Ques 4. 7.30 = 5.11 x (w x 1000 / M x V )

7.30 = 5.11 x (7.20 x 1000 / M x 25)

M = 201.6 g/mol

Ques 5. A face centered cubic unit cell have 4 atoms. It can be derived as follows:

The contribution of each atom on the corner of a unit cell= 1/8

The contribution of each atom on the face of a unit cell = 1/2

Since, in a face centered cubic unit cell, total number of corners are 8 and faces are 6.

So, the number of atoms involved on the corner of the fcc unit cell=

1/8 x 8 = 1

Similarly, the number of atoms involved on the faces of the fcc unit cell=

1/2 x 6 = 3

Hence, total no. of atoms involved in a FCC unit cell =

1 + 3 = 4

Thus, total no. of atoms ina FCC unit cell is 4.

Ques 5. The metal is presnt in FCC so number of M = 4

Also Oxygen are pesent in tetrahedral voids = 8

So M4O8 = MO2 is the correct formula

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