14.14 水流离失所造成的天然气收集

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  水流离失所造成的煤气收集

  

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  What is the pressure?
  ::压力是什么?

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  You need to do a lab where hydrogen is generated. In order to calculate the yield of gas, you have to know the pressure inside the tube where the gas is collected. But how can you get a barometer in there? Very simple: you don’t. All you need is the in the room. As the gas pushed out the water, it is pushing against the atmosphere, so the pressure inside is equal to the pressure outside.
  ::您需要在产生氢的实验室里做一个实验。 为了计算气体的产量, 您必须知道气体聚集处的管内压力。 但是, 您如何在那里获得气压计? 很简单: 您不需要。 您只需要在房间里。 当气体排出水面时, 它正在向大气推进, 所以里面的压力与外面的压力是相等的 。

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  Gas Collection by Water Displacement
  ::水流离失所造成的煤气收集

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  Gases that are produced in laboratory experiments are often collected by a technique called water displacement (see Figure ). A bottle is filled with water and placed upside-down in a pan of water. The reaction flask is fitted with rubber tubing which is then fed under the bottle of water. As the gas is produced in the reaction flask, it exits through the rubber tubing and displaces the water in the bottle. When the bottle is full of the gas, it can be sealed with a lid.
  ::在实验室实验中产生的气体通常由一种称为脱水的技术收集(见图 ) 瓶装水,倒置在一个水池中,反应瓶装有橡胶管,然后在水瓶下喂食,气体在反应瓶中生产,通过橡胶管流出,将水倒置在瓶中,当瓶装满气体时,可以用盖子封住。

  

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  A gas produced in a chemical reaction can be collected by water displacement.
  ::在化学反应中产生的气体可以通过水流转移来收集。

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  Because the gas is collected over water, it is not pure but is mixed with vapor from the of the water. Dalton’s law can be used to calculate the amount of the desired gas by subtracting the contribution of the water vapor.
  ::由于气体是通过水收集的,因此它不是纯净的,而是与水中的蒸气混合。 道尔顿的法律可以用来计算所需气体的数量,方法是减去水蒸气的贡献。

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  $$\begin{array}{rl}{P}_{\text{Total}}& =P_g+P_{H_{2}O}{P}_g\text{ is the pressure of the desired gas}\\ P_g& =P_{\text{Total}}-P_{H_{2}O}\end{array}$$

  
  ::PTal=Pg+PH2OPg 是所需气体Pg=PTotatal-PH2O的压力

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  In order to solve a problem, it is necessary to know the of water at the temperature of the reaction (see Table ). The sample problem illustrates the use of Dalton’s law when a gas is collected over water.
  ::为了解决问题,必须在反应温度下了解水的情况(见表 ) 。 抽样问题说明了在从水中收集气体时使用道尔顿定律的情况。

  Vapor Pressure of Water (mmHg) at Selected Temperatures (°C)

  0	5	10	15	20	25	30	35	40	45	50	55	60	65	70
  4.58	6.54	9.21	12.79	17.54	23.76	31.82	42.18	55.32	71.88	92.51	118.04	149.38	187.54	233.7

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  Sample Problem: Gas Collected by Water Displacement
  ::问题:因水流离失所而收集的气体

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  A certain experiment generates 2.58 L of hydrogen gas, which is collected over water. The temperature is 20°C and the atmospheric pressure is 98.60 kPa. Find the volume that the dry hydrogen would occupy at STP.
  ::某种实验产生2.58升氢气,从水中收集,温度为20°C,大气压力为98.60千帕。

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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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  • $\begin{array}{r}{V}_{\text{Total}}=2.58\text{ L}\end{array}$
    ::VTalal=2.58升
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  • $\begin{array}{r}T={20}^{\circ }\text{C}=293\text{ K}\end{array}$
    ::T=20°C=293K
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  • $\begin{array}{r}{P}_{\text{Total}}=98.60\text{ kPa}=739.7\text{ mmHg}\end{array}$
    ::PTalal=98.60 kPa=739.7毫米Hg

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  Unknown
  
  ::未知

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  • $\begin{array}{r}{V}_{H_2}\text{at}STP=?\text{ L}\end{array}$
    ::在STP=L的VH2吗?

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  The atmospheric pressure is converted from kPa to mmHg in order to match units with the table. The sum of the pressures of the hydrogen and the water vapor is equal to the atmospheric pressure. The pressure of the hydrogen is found by subtraction. Then, the volume of the gas at STP can be calculated by using the .
  ::将大气压力从 kPa 转换为 mmHg , 以便与表格中的单位匹配。 氢和水蒸气的压力总和等于大气压力。 氢的压力通过减法找到。 然后, SPT 的气体量可以通过使用 来计算 。

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  Step 2: Solve.
  ::步骤2:解决。

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  $$\begin{array}{r}{P}_{H_2}=P_{\text{Total}}-P_{H_{2}O}=739.7\text{ mmHg}-17.54\text{ mmHg}=722.2\text{ mmHg}\end{array}$$

  
  ::PH2=PTPT-PH2O=739.7毫米Hg-17.54毫米Hg=722.2毫米Hg

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  Now the combined gas law is used, solving for $\begin{array}{r}{V}_2\end{array}$ , the volume of hydrogen at STP.
  ::现在使用联合天然气法, 解决V2,在STTP的氢气量。

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  $$\begin{array}{r}{V}_2=\frac{P_1\times V_1\times T_2}{P_2\times T_1}=\frac{722.2\text{ mmHg}\times 2.58\text{ L}\times 273\text{ K}}{760\text{ mmHg}\times 293\text{ K}}=2.28\text{ L }{H}_2\end{array}$$

  
  ::V2=P1xV1xT2P2xT1=722.2毫米Hg×2.58 Lx273 K760毫米Hgx293 K=2.28 LH2

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

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  If the hydrogen gas were to be collected at STP and without the presence of the water vapor, its volume would be 2.28 L. This is less than the actual collected volume because some of that is water vapor. The conversion using STP is useful for stoichiometry purposes.
  ::如果氢气在STP收集,如果没有水蒸气,其体积将为2.28升。 由于其中一些是水蒸气,这低于实际收集的体积。 使用STP的转换对测量技术有用。

   

   

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  Summary
  ::摘要

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  • The vapor pressure due to water in a sample can be corrected for in order to get the true value for the pressure of the gas.
    ::样本中因水造成的蒸气压力是可以纠正的,以便获得气体压力的真正价值。

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  Review
  ::回顾

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  1. Why is gas collected over water not pure?
     ::为什么在水上收集的气体不是纯净的?
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  2. Why would we want to correct for water vapor?
     ::为什么我们要纠正水蒸气?
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  3. In a lab, 2.20 L of gas is collected over water at a temperature of 30°C and a total pressure of 735.43 mmHg. Find the volume that the dry nitrogen of gas would occupy at STP.
     ::在实验室中,在温度为30°C和总压力为735.43毫米Hg的温度下,从水面上收集2.20升气体。

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  Explore More
  ::探索更多

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  Use the resource below to answer the questions that follow.
  ::利用以下资源回答以下问题。

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  1. What was the thistle tube used for?
     ::管是用来做什么的?
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  2. How did the instructor tests for oxygen?
     ::教官如何测试氧气?
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  3. What would have happened to the splint if carbon dioxide had been collected?
     ::如果二氧化碳被收集起来,板块会怎么样?