APPENDIX XII GENERAL CHEMISTRY STUDY SHEETS GENERAL CHEMISTRY STUDY SHEET NO. 15

Question

APPENDIX XII GENERAL CHEMISTRY STUDY SHEETS GENERAL CHEMISTRY STUDY SHEET NO. 15 1. If the mole fraction ofA is 0.200 in a solution of A dissolved in B, then calculate the vapor pressure of the solution at 50°C. The vapor pressure of pure A 800 torr and B 600 torr. If the atmospheric pressure is 760 torr, would this solution be boiling at 50°C? 2. Calculate the vapor pressure (at 25°C) of a solution containing 4.57 g of glucose CH,20g) dissolved in 25.2 g of water. The vapor pressure of water at 25 C is 23.8 torr and that of glucose (a nonvolatile compound) is 0.0 torr 3. How much (in torr) has the vapor pressure been lowered in question 2? 4. What are the boiling and melting points of a 0.222 m glucose (non-electrolyte) 0.000°C, and bp solution? For water K, 0.521°C/m, Kr 1.858°C/m, mp - 100.000 °C 5. How many grams of ethylene glycol (CH,OHCH,OH) must be added to one gallon (3779 g) of water to give a freezing point of-15°C? K, of H2O is 1.858 C/m 6. A 2.00 m solution of naphthalene (non-volatile) in benzene would boil at what temperature. For benzene: K, 2.61°C/m and bp 80.2°C. 7. If 0.131 g of compound X were dissolved in 25.4 g of water, then what is the molar mass of X if the molality of the solution were found to be 0.056 m? 8. If 6.43 mg of compound Z were dissolved in 78.1 mg of camphor and the melting point of that solution were found to be 158.5°C, then calculate the molar mass ofZ. For camphor: mp-179.5 and Kf-40.0°C/m. 9. If 3.19 g of a starch (MM-32,400 g/mol) were dissolved in 100 mL of water (K, of H,0 is 1.858'C/m) solution at 25°C, then: a) calculate its osmotic pressure in torr b) the amount of freezing (which is true for very dilute solutions). c) why are osmotic pressure techniques preferred over freezing point lowering techniques for molar mass determination of high molar mass compounds? 3.50 atm at 20.0°C in which 5.00 g are dissolved in 100. mL of aqueous solution. ter K, - 1.86 Clm and fp -0.00°c 10. Calculate the molar mass of compound W if it has an osmotic pressure of 11. For the following aqueous solutions calculate the osmolality and F. pt. For wa- a) 2.00 m Nal e) 2.00 m Na PO b) 2.00 m Na SO d) 2.00 m glucose (non-electrolyte)

Explanation / Answer

1)p=mole fraction X vapour pressure at pure state

p=0.2X800+(1-0.2)X600=640

2)Delta p=mole fractionX p=(4.57/180)/(25.2/18)X23.8 =0.431 torr

3)vapour pressure lowered=0.431torr

4)T_b=100+(0.521X0.222)=100.115 C

T_m=0+(1.858X0.222)=0.351 C

5)m=15/1.585=9.46

m=(M/180)/(3779/18)

M=8.113 g

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