benzene. The freezing point of the solution is 1.05℃ below that of pure benzene. What are the molar mass and molecular formula of this compound?
Solution: bB?1.05K?0.206mol?kg?1 ?15.10K?kg?molMr?7.85g?1 ?127g?mol0.301kg?0.206mol?kg-1?1Since the formula mass of C5H4 is 64g?moland the molar mass is found to be
127g?mol?1 , the molecular formula of the compound is C10H8.
5. Ethylene glycol (EG) CH2(OH)CH2(OH), is a common automobile antifreeze. it is cheap, water-soluble, and fairly nonvolatile (b.p.197℃).Calculate the freezing point of a solution
containing 651g of this substance in 2505g of water. Would you keep this substance in your car radiator during the summer? The molar mass of ethylene glycol is 62.01g.
Solution: M(EG)=62.01g·mol
-1
651g/62.01g?mol-1
b(EG)??4.19mol?kg?12.505kg?Tf?1.86K?kg?mol?1?4.19mol?kg?1?7.79KTf??7.79oC
?Tb?0.512K?kg?mol?1?4.19mol?kg?1?2.15KTb?102.15oC
Because the solution will boil at 102.15℃,it would be preferable to leave the antifreeze in your car radiator in summer to prevent the solution from boiling.
6. A solution is prepared by dissolving 35.0g of hemoglobin (Hb) in enough water to make up one liter in volume.If the osmotic pressure of the solution is found to be 10.0mmHg at 25℃,calculate the molar mass of hemoglobin.
Solution: the concentration of the solution:
101.3kPaΠ760mmHg?4?1c(Hb)???5.38?10mol?LRT8.314kPa?L?mol?1?K-1?(273?25)K10.mmHg?M(Hb)?35.0g?6.51?104g?mol?1 -4-15.38?10mol?L?1L7. A 0.86 percent by mass solution of NaCl is called “physiological saline” because its osmotic pressure is equal to that of the solution in blood cell. Calculate the osmotic pressure of this solution at normal body temperature (37℃). Note that the density of the saline solution is 1.005g /mL.
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0.86g?1.005g?mL?11000mLSolution: c(NaCl)?100g??0.148mol?L?1 ?11L58.5g?molΠ?icBRT ?2?0.148mol?L?1?8.314kPa?L?mol?1?K-1?(273?37)K
?763kPa
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基础化学第二章后习题标准答案
