章节大纲

  • Nutritional label showing peanut butter serving size, protein, fat, sugar, and other nutrients.

    Is there anything healthy in this jar?
    ::这罐子里有健康的东西吗?

    Packaged foods that you eat typically have nutritional information provided on the label.  The label on a jar of peanut butter (shown above) reveals that one serving size is considered to be 32 g.  The label also gives the masses of various types of compounds that are present in each serving.  One serving contains 7 g of , 15 g of fat, and 3 g of sugar.  By calculating the fraction of protein, fat, or sugar in one serving of size of peanut butter and converting to percent values, we can determine the composition of the peanut butter on a percent by mass basis.
    ::您所食的包装食品通常在标签上提供营养信息。 花生酱罐头上的标签( 如上所示) 显示, 一种服务尺寸被认为是32克。 标签还给出了每种服务中存在的各种化合物的总量。 一种服务包含7克、 15克脂肪和3克糖。 通过计算花生酱大小之一的蛋白质、 脂肪或糖分数, 并转换成百分比值, 我们可以按质量来决定花生酱的成分。

    Percent Composition
    ::构成百分比

    Chemists often need to know what are present in a and in what percentage.  The percent composition is the percent by mass of each element in a compound.  It is calculated in a similar way that we just indicated for the peanut butter.
    ::化学家通常需要知道一个百分比中存在什么。 百分比构成是化合物中每个元素的重量百分比。 计算方法与我们刚刚为花生酱表示的相同。

    %   by mass = mass of element mass of compound × 100 %

    ::%,按质量=化合物的元素质量×100%

    Percent Composition From Mass Data
    ::质量数据构成百分比百分比

    The sample problem below shows the calculation of the percent composition of a compound based on mass data.
    ::下面的抽样问题显示了根据质量数据计算化合物成份百分比的方法。

    Sample Problem One: Percent Composition from Mass
    ::抽样问题一:质量构成百分比

    A certain newly synthesized compound is known to contain the elements zinc and oxygen.  When a 20.00 g sample of the sample is decomposed, 16.07 g of zinc remains.  Determine the percent composition of the compound.
    ::已知某种新合成的化合物含有锌和氧元素,当对样本的20.00克样本进行分解时,有16.07克的锌残余物,确定化合物的成分百分比。

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

    Known
    ::已知已知

    • mass of compound = 20.00 g
      ::化合物质量=20.00克
    • mass of Zn = 16.07 g
      ::Zn 质量= 16.07克

    Unknown
    ::未知

    • percent Zn = ? %
      ::Zn = = ?%
    • percent O = ? %
      ::O % = * %

    Subtract to find the mass of oxygen in the compound.  Divide each element’s mass by the mass of the compound to find the percent by mass.
    ::减号以找到化合物中的氧气质量。 将每个元素的质量除以化合物的质量, 以根据质量找到百分比 。

    Step 2: Calculate.
    ::第2步:计算。

    Mass of oxygen = 20.00   g − 16.07   g = 3.93   g O %   Zn = 16.07   g Zn 20.00   g × 100 % = 80.35 %   Zn %   O = 3.93   g O 20.00   g × 100 % = 19.65 %   O

    ::氧气质量=20.00 g-16.07 g=3.93 g On Zn=16.07 g Zn=16.07 g Zn0.00 gzn20.00 gx10080.35% Zn% O=3.93 g O20.00 gx10019.65% O

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

    The calculations make sense because the sum of the two percentages adds up to 100%.  By mass, the compound is mostly zinc.
    ::计算是有道理的,因为这两个百分比的总和加起来等于100%。 从质量上看,化合物主要是锌。

    Percent Composition From a Chemical Formula
    ::来自化学公式的成分百分比

    The percent composition of a compound can also be determined from the formula of the compound.  The subscripts in the formula are first used to calculate the mass of each element in one mole of the compound.  That is divided by the of the compound and multiplied by 100%.
    ::化合物的百分率构成也可以从化合物的公式中确定。公式中的下标首先用来计算化合物内一个摩尔中的每个元素的质量。该数值除以化合物,再乘以100%。

    %   by mass  = mass of element in   1   mol molar mass of compound × 100 %

    ::%,按质量 = 化合物1毫摩尔质量中元素的重量×100%计算

    The percent composition of a given compound is always the same as long as the compound is pure.
    ::某一化合物的成份百分比始终相同,只要该化合物是纯净的。

    Sample Problem Two: Percent Composition from Chemical Formula
    ::抽样问题二:化学品公式的构成百分比

    Dichlorineheptoxide (Cl 2 O 7 ) is a highly reactive compound used in some organic synthesis reactions.  Calculate the percent composition of dichlorineheptoxide.
    ::二氯代二氧(Cl2O7)是一种高反应性化合物,用于某些有机合成反应。计算二氯代二氧的成份百分比。

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

    Known
    ::已知已知

    • mass of Cl in 1 mol Cl 2 O 7 = 70.90 g
      ::1 mol Cl2O7 = 70.90 克,1 mol Cl2O7 = 70.90 克,1 mol Cl2O7 = 70.90 克
    • mass of O in 1 mol Cl 2 O 7 = 112.00 g
      ::1 mol Cl2O7 = 112.00 克
    • molar mass of Cl 2 O 7 = 182.90 g/mol
      ::Cl2O7 = 182.90 克/摩尔的摩度

    Unknown
    ::未知

    • percent Cl = ? %
      ::Cl = = 百分比 Cl = ?
    • percent O = ? %
      ::O % = * %

    Calculate the percent by mass of each element by dividing the mass of that element in 1 mole of the compound by the molar mass of the compound and multiplying by 100%.
    ::按每个元素的质量计算百分比,将该元素的重量除以化合物的摩尔质量,将该元素的重量除以化合物的摩尔质量,再乘以100%。

    Step 2: Calculate.
    ::第2步:计算。

    %   Cl = 70.90   g Cl 182.90   g × 100 % = 38.76 %   Cl %   O = 112.00   g O 182.90   g × 100 % = 61.24 %   O

    ::% Cl=70.90 g Cl182.90 g Cl182.90 g ×10038.76% Cl% O=112.00 g O 182.90 g ×100 ×61.24% O

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

    The percentages add up to 100%.
    ::百分比加起来达到100%。

    Percent composition can also be used to determine the mass of a certain element that is contained in any mass of a compound.  In the previous sample problem, it was found that the percent composition of dichlorineheptoxide is 38.76% Cl and 61.24% O.  Suppose that you needed to know the masses of chlorine and oxygen present in a 12.50 g sample of dichlorineheptoxide.  You can set up a conversion factor based on the percent by mass of each element.
    ::百分率成分也可以用来确定化合物任何质量所含某一元素的质量。在以前的样本问题中,发现二氯甲烷的成分百分比为38.76% Cl和61.24% O。假设你需要了解二氯乙烷12.50克样本中的氯和氧的成分。你可以根据每种元素的质量百分比设定一个转换系数。

    12.50   g Cl 2 O 7 × 38.76   g Cl 100   g Cl 2 O 7 = 4.845   g Cl 12.50   g Cl 2 O 7 × 61.24   g O 100   g Cl 2 O 7 = 7.655   g O

    ::12.50克 Cl2O7×38.76克 Cl100克 Cl2O7=4.845克 Cl12.50克 Cl2O7×61.24克 O100克 Cl2O7=7.655克

    The sum of the two masses is 12.50 g, the mass of the sample size.
    ::两个质量的总和是12.50克,即样本大小的质量。

     

     

    Science Friday: Stained Glass Conservation
    ::星期五:染色玻璃保护

    Stained glass from the Middle Ages is often hundreds of years old. Unfortunately, many of these relics are in need of cleaning and maintenance. In this video by Science Friday, conservator Mary Higgins discusses the methods used to protect the stained glass.
    ::中世纪的染色玻璃往往有数百年的历史。 不幸的是,许多这些遗迹需要清理和维护。 在科学星期五的录像中,玛丽·希金斯(Mary Higgins)讨论了保护染色玻璃的方法。

     

     

    Summary
    ::摘要

    • Processes are described for calculating the percent composition of a material based on mass or on chemical composition.
      ::根据质量或化学成分计算材料成份百分比的过程。

    Review
    ::回顾

    1. What is the formula for calculating percent composition?
      ::计算百分比构成的公式是什么?
    2. What information do you need to calculate percent composition by mass?
      ::您需要什么信息来计算质量的百分数构成 ?
    3. What do subscripts in a chemical formula tell you?
      ::化学公式中的下标告诉你什么?