16.15 沸点升高

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  沸点升高

  

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  Does adding salt help water boil?
  ::添加盐能帮助煮水吗?

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  Salt is often added to water when preparing spaghetti or other pasta. One reason is to add flavor to the food. Some people believe that the addition of salt increases the boiling point of the water. Technically, they are correct, but the increase is rather small. You would need to add over 100 grams of NaCl to a liter of water to increase the boiling point a couple of degrees, which is just not healthy.
  ::在准备意大利面或其他意大利面或其他意大利面时,盐往往加到水中。一个原因是增加食物的口味。有些人认为加盐会增加水的沸点。从技术上讲,它们是正确的,但增加量相当小。你需要在一公升水中添加100多克NaCl,以增加几度的沸点,这实在是不健康的。

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  Boiling Point Elevation
  ::沸点升高

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  Figure shows the phase diagram of a solution and the effect that the lowered has on the boiling point of the solution compared to the solvent . In this case, the solution has a higher boiling point than the pure solvent. Since the vapor pressure of the solution is lower, more must be supplied to the solution to bring its vapor pressure up to the pressure of the external atmosphere. The boiling point elevation is the difference in temperature between the boiling point of the pure solvent and that of the solution. On the graph, the boiling point elevation is represented by $\begin{array}{r}\mathrm{\Delta }{T}_b\end{array}$ .
  ::图中显示了溶液的相位图,以及降价对溶剂的沸点比溶剂对溶剂的沸点的影响。在此情况下,溶液的沸点高于纯溶剂。由于溶液的蒸汽压力较低,必须更多地提供给溶液,使其蒸汽压力达到外部大气的压力。沸点升高是纯溶剂的沸点与溶液的沸点之间的温度差异。在图中,沸点升高由 +Tb 表示。

  

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  The magnitude of the boiling point elevation, $\begin{array}{r}\mathrm{\Delta }{T}_b\end{array}$ , is directly proportional to the ,  $\begin{array}{r}m\end{array}$ , of the solution. The equation is:
  ::沸点高度的大小, Tb, 与溶液的 m 成正比。 方程式是 :

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  $$\begin{array}{r}\mathrm{\Delta }{T}_b=i\times K_b\times m\end{array}$$

  
  ::*Tb=i×Kb×m * *Tb=i×Kb×m*

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  In van't Hoff factor,  $\begin{array}{r}i\end{array}$ , the moles of particles per moles of solute . For nonelectrolytes the van’t Hoff factor is equal to one. For strong electrolytes the van’t Hoff factor is the number of dissolved per formula unit . 
  ::在 van't Hoff 系数中,i, 溶液中每颗粒的摩尔。对于非电子化分子来说,凡特霍夫系数等于1。对于强电解系数,凡特霍夫系数是每个公式单位的溶解数。

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  $$\begin{array}{r}i=\frac{\text{number of particles in solution after dissociation}}{\text{number of formula units initially dissolved in solution}}\end{array}$$

  
  ::i=在溶解初期溶解的公式单位分离数后溶解的粒子数

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  The proportionality constant, $\begin{array}{r}{K}_b\end{array}$ , is called the molal boiling-point elevation constant . It is a constant that is equal to the change in the boiling point for a 1-molal solution of a nonvolatile molecular solute. For water, the value of  $\begin{array}{r}{K}_b\end{array}$ is 0.512°C/ m . So the boiling temperature of a 1-molal aqueous solution of any nonvolatile molecular solute is 100.512°C.
  ::相称性常数 Kb 被称为 olal 沸点高度常数 。 它等于非挥发分子溶液1毫升溶液的沸点变化。 对于水, Kb 值为 0. 512 °C/ m。 因此任何非挥发分子溶液1毫升溶液的沸点温度为 100.512°C 。

   

   

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   Does water boil at 100ºC everywhere? Try it out with this simulation: 
  ::水在100摄氏度处沸腾吗?

   

   

   

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  Summary
  ::摘要

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  • Boiling point elevation is defined.
    ::确定沸点高度。
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  • Calculations involving the molal boiling point elevation constant are outlined.
    ::概列涉及软体沸点高度常数的计算。

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  Review
  ::回顾

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  1. Why does the addition of a solute to water increase the boiling point?
     ::为什么在水中添加溶液会增加沸点呢?
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  2. What does the molal boiling point elevation constant tell us?
     ::软骨沸点高高常数告诉我们什么?
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  3. The addition of KCl raises the boiling point of 1.0 kg water by 3.014°C. How many moles of KCl were added?
     ::添加 KCl 将 1.0 千克水的沸点提高3. 014 °C。 添加了多少个KCl 摩尔?