16.17 使用协调属性计算摩尔质量

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• 选择节使用对调属性计算模型质量

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  使用对调属性计算模型质量

  

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  How much antifreeze is needed?
  ::需要多少抗冻剂?

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  We know that we can put antifreeze into a radiator and keep an engine from up. By knowing how cold it will get and how much water is in the radiator, we can determine how much antifreeze to add to achieve our desired . We can do this because we know what the antifreeze is. Can we switch things around and get some information about the properties of the antifreeze (such as its molecular weight) from the freezing point decrease? It turns out that we can do this fairly easily and accurately.
  ::我们知道,我们可以将抗冻剂放入散热器中,并保持发动机的停放。通过知道辐射器中的冷度和水量,我们可以确定需要增加多少抗冻剂来实现我们的愿望。我们可以这样做,因为我们知道防冻剂是什么。我们可以把东西换掉,从冷点的减少点获得一些关于抗冻剂特性(如分子重量)的信息吗?事实证明,我们可以很容易和准确地做到这一点。

  

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  Calculating Molar Mass
  ::计算摩尔质量

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  In the laboratory, freezing point or boiling point data can be used to determine the of an unknown solute . Since we know the relationship between a decrease in freezing point and the of solute, if we dissolve a known mass of our unknown solute into a known amount of solvent , we can calculate the molar mass of the solute. The  $\begin{align*}K_f\end{align*}$ or  $\begin{align*}K_b\end{align*}$ of the solvent must be known. We also need to know if the solute is an electrolyte or a nonelectrolyte . If the solvent is an electrolyte, you would need to know the number of is produced when it dissociates.
  ::在实验室中,冷点或沸点数据可以用来确定未知溶液。由于我们知道冷点减少和溶液减少之间的关系,如果我们将未知溶液的已知质量溶液溶解到已知的溶剂中,我们可以计算溶液的摩尔质量。必须知道溶剂的Kf或Kb。我们还需要知道溶液是电解剂还是非电解剂。如果溶剂是电解剂,你就需要知道溶剂分离时所生产的数量。

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  Sample Problem: Molar Mass from Freezing Point Depression
  ::抽样问题:来自冷冻点萧条的摩尔弥撒

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  To make a solution, 38.7 g of a nonelectrolyte is dissolved into 218 g of water. The freezing point of the solution is measured to be -5.53°C. Calculate the molar mass of the solute.
  ::为了解决问题,将38.7克非电解剂溶解为218克水,溶解剂的冷点测量为-5.53°C。计算溶液的摩尔质量。

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  Step 1: List the known quantities and plan the problem.
  ::第1步:列出已知数量并规划问题。

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  Known
  ::已知已知

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  • $\begin{align*}\Delta T_f=-5.53^\circ \ \text{C}\end{align*}$
    ::Tf5.53C
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  • mass H ₂ O 218 g = 0.218 kg
    ::H2O 218克 = 0.218千克
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  • mass solute = 38.7 g
    ::溶液质量 = 38.7克
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  • $\begin{align*}K_f(\text{H}_2\text{O})=-1.86^\circ \ \text{C}/m\end{align*}$
    ::Kf(H2O)1.86C/m

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  Unknown
  ::未知

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  • molar mass solute = ? g/mol
    ::摩拉质量溶液=? g/mol

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  Use the freeing point depression $\begin{align*}(\Delta T_f)\end{align*}$  to calculate the of the solution. Then use the molality equation to calculate the moles of solute. Then divide the grams of solute by the moles to determine the molar mass.
  ::使用自由点抑郁( Tf) 来计算溶液的解答。 然后使用软体方程来计算溶液的摩尔。 然后用摩尔来计算溶液的摩尔。 然后用摩尔来区分溶液的克数, 以决定摩尔质量 。

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  Step 2: Solve.
  ::步骤2:解决。

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  $$\begin{align*}m=\frac{\Delta T_f}{K_f} &=\frac{-5.53^\circ \text{C}}{-1.86^\circ \text{C}/m}=2.97 \ m\\ \text{mol solute} &= m \times \text{kg H}_2\text{O}=2.97 \ m \times 0.218 \text{ kg} = 0.648 \text{ mol}\\ \frac{38.7 \text{ g}}{0.648 \text{ mol}} &= 59.7 \text{ g/mol}\end{align*}$$
  ::mTfKf5.53C-1.86C/m=2.97毫摩洛溶胶=mxkH2O=2.97mx0.218千克=0.648 mol38.7 g0.648 mol=59.7 g/mol

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  Step 3: Think about your result.
  ::步骤3:想想你的结果。

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  The molar mass of the unknown solute is 59.7 g/mol. Knowing the molar mass is an important step in determining the identity of an unknown. A similar problem could be done with the change in boiling point.
  ::未知溶液的摩尔质量为59.7克/摩尔。 了解摩尔质量是确定未知物身份的一个重要步骤。 随着沸点的改变,也可能出现类似的问题。

   

   

   

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  Summary
  ::摘要

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  • The molar mass of solute can be determined  using the formula for freezing point depression or boiling point elevation and solving for the moles of solute in solution.
    ::溶液的摩尔质量可以用冷点压抑或沸点升高和溶液溶液摩尔的溶液溶液溶液溶液溶液溶液溶液的公式来确定。

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  Review
  ::回顾

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  1. What do we need to know about the solvent to use this technique?
     ::使用这种技术的溶剂需要知道什么?
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  2. Can the molar mass be calculated from the boiling point or freezing point of solutions that contain electrolytes?
     ::摩尔质量能否从含有电解液的沸点或冷点溶液中计算出来?
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  3. A solution is made by dissolving 34.41 g of an unknown nonelectrolyte compound in 280.0 g benzene. The boiling point of the solution is 93.2 °C. Benzene has a boiling point of 80.1 °C and molal boiling-point elevation constant  of 2.53 °C/m. What is the molar mass of the solute?
     ::溶液的沸点为93.2°C。 苯的沸点为80.1°C,软质沸点高度常数为2.53°C/m。 溶液的摩尔质量是多少?