LAB DATA Mass (g) of p-Dichlorobenzene used=9.53 Initial Mass (g) of opened samp

Question

LAB DATA
Mass (g) of p-Dichlorobenzene used=9.53
Initial Mass (g) of opened sample tube=13.9161
Mass (g) (Sample tube - Sample 1)=13.2459
Mass (g) of sample tube with remaining sample=13.2459
Mass (g) of sample tube - both samples=12.7459
Freezing point (°C) of pure p-Dichorobenzene=53.1
Freezing point (°C) of Solution 1=50.1
Freezing point (°C) of Solution 2=48.1
Calculations
1. What is the mass (g) of UNKNOWN added to Solution 1?
2. What is the total mass (g) of UNKNOWN in Solution 2?
3. What is the Freezing Point Depression (°C) of Solution 1?
4.What is the Freezing Point Depression (°C) of Solution 2?
5. Unknown molecular weight (g/mol) calculated from pure PDB and Solution 1?
6. Unknown molecular weight (g/mol) calculated from pure PDB and Solution 2?
7. Unknown average molecular weight (g/mol)?


LAB DATA
Mass (g) of p-Dichlorobenzene used=9.53
Initial Mass (g) of opened sample tube=13.9161
Mass (g) (Sample tube - Sample 1)=13.2459
Mass (g) of sample tube with remaining sample=13.2459
Mass (g) of sample tube - both samples=12.7459
Freezing point (°C) of pure p-Dichorobenzene=53.1
Freezing point (°C) of Solution 1=50.1
Freezing point (°C) of Solution 2=48.1
Calculations
1. What is the mass (g) of UNKNOWN added to Solution 1?
2. What is the total mass (g) of UNKNOWN in Solution 2?
3. What is the Freezing Point Depression (°C) of Solution 1?
4.What is the Freezing Point Depression (°C) of Solution 2?
5. Unknown molecular weight (g/mol) calculated from pure PDB and Solution 1?
6. Unknown molecular weight (g/mol) calculated from pure PDB and Solution 2?
7. Unknown average molecular weight (g/mol)?


LAB DATA
Mass (g) of p-Dichlorobenzene used=9.53
Initial Mass (g) of opened sample tube=13.9161
Mass (g) (Sample tube - Sample 1)=13.2459
Mass (g) of sample tube with remaining sample=13.2459
Mass (g) of sample tube - both samples=12.7459
Freezing point (°C) of pure p-Dichorobenzene=53.1
Freezing point (°C) of Solution 1=50.1
Freezing point (°C) of Solution 2=48.1
Calculations
1. What is the mass (g) of UNKNOWN added to Solution 1?
2. What is the total mass (g) of UNKNOWN in Solution 2?
3. What is the Freezing Point Depression (°C) of Solution 1?
4.What is the Freezing Point Depression (°C) of Solution 2?
5. Unknown molecular weight (g/mol) calculated from pure PDB and Solution 1?
6. Unknown molecular weight (g/mol) calculated from pure PDB and Solution 2?
7. Unknown average molecular weight (g/mol)?

Explanation / Answer

1. The mass of unknown added to solution 1 = 13.9161 - 13.2459 = 0.6702 g

2. The mass of unknown added to solution 2 = 13.2459 - 12.7459 = 0.5 g

3. The freezing point depression of solution 1 = 50.1 - 53.1 = -3 oC

4. The freezing point depression of solution 2 = 48.1 - 53.1 = -5 oC

5. The freezing point depression constant for p-dichlorobenzene = 7.10 oC/m

molality of solution 1 = (0.6702 g/M1)/9.53 g = 0.070325/M1 m, where M1 is the molecular weight of unknown in solution 1

From freezing point depression, -3 oC = -7.10 oC/m * 0.070325/M1 m

Therefore, M1 = 166.44 g/mol

6. molality of solution 2 = (0.5/M1)/9.53 g = 0.052466/M2 m, where M2 is the molecular weight of unknown in solution 2

From freezing point depression, -5 oC = -7.10 oC/m * 0.052466/M2 m

Therefore, M2 = 74.50 g/mol

7. The average molecular weight of unknown = (166.44+74.50)/2 = 120.47 g/mol

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