Name: chemical formula mass and percent composition
Uploaded: 2020-09-03T13:38:26.000Z
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Formula Mass and Mole Concepts of Compounds

Наименьшей репрезентативной единицей соединения является молекула представленная химической формулой. Атомные массы всех атомов в химической формуле при сложении дают молекулярную массу соединения, измеренную в единицах атомной массы. Например, чтобы найти молекулярную массу сахарозы или столового сахара, необходимо атомную массу каждого элемента умножить на количество атомов соответствующего элемента.В сумме мы получим молекулярную массу сахарозы. Масса всех молекул присутствующих в одном моле химического соединения, называется его молярной массой, измеряемой в граммах на моль. Молярная масса соединения численно равна его молекулярной массе Например, сахароза с молекулярной массой 342, 3 атомной единицы массы, будет иметь молярную массу 342, 3 грамма на моль.Знание фактического количества молекул или частиц, присутствующих в химическом веществе, имеет основополагающее значение для понимания его состава, взаимодействий и комбинаций. Однако в данном образце соединения подсчет фактического количества молекул обычными средствами нецелесообразен. Используя соотношение между молярной массой, молями и числом Авогадро, можно рассчитать общее количество присутствующих молекул.Согласно концепции, молярная масса соединения эквивалентна массе одного моля соединения, содержащего 6, 022 x 10^23 частиц. Следовательно, 342, 3 грамма сахарозы содержат 6, 022 x 10^23 молекул сахарозы. Однако, если образец сахарозы весит, например, 150 граммов, то количество молекул можно определить расчетным путем с использованием метода перекрестного умножения.Результат показывает, что 150 граммов сахарозы содержат 2, 63 x 10^23 молекул сахарозы. Процентное содержание каждого элемента в соединении может быть выражено в массовых процентах. Для их вычисления, масса элемента в одном моле соединения делится на общую массу одного моля соединения и преобразуется в проценты.На практике для расчета массового процента водорода в сахарозе в формулу включается общая масса атомов водорода и общая масса молекул сахарозы. Расчетное значение показывает, что сахароза содержит 6, 4 мас.водорода.

Формула массы и молярные концепции соединений

" <h4>Атомная масса формулы ковалентных соединений </h4>
 
 Химические формулы представляют собой элементный состав веществ. Для ковалентных соединений формула представляет числа и типы атомов, составляющих одну молекулу вещества; поэтому масса формулы может быть правильно отнесена к молекулярной массе. Молекулярная формула хлороформа (CHCl3), ковалентного соединения, указывает на то, что одна молекула содержит один атом углерода, один атом водорода и три атома хлора. Средняя молекулярная масса молекулы хлороформ равна сумме средних атомных масс этих атомов: 
 
 <img alt=""Eq1"" src=""https://www.jove.com/files/core/CDNSource/lessons/1017/1017_Equations-01.png"" style=""height: 40px;"" />
 
 <h4>Формула массы ионных соединений </h4>
 
 Ионные соединения состоят из дискретных катионов и анионов, которые объединяются в отношения для получения электрически нейтральной массы. Масса формулы для ионного соединения рассчитывается так же, как масса формулы для ковалентных соединений: Путем суммирования средних атомных масс всех атомов в формуле соединения. Однако формула для ионного соединения не представляет состав дискретной молекулы, поэтому она может быть неправильно отнесена к ‘молекулярной массе’. 
 
 Например, обычная столовая соль или хлорид натрия (NaCl) представляет собой ионное соединение, состоящее из катионов натрия (Na+) и анионов хлорида (CL-), Объединенных в соотношении 1:1. Масса формулы для этого соединения вычисляется путем добавления средних атомных масс его составных элементов: 
 
 <img alt=""Eq2"" src=""https://www.jove.com/files/core/CDNSource/lessons/1017/1017_Equations-02.png"" style=""height: 40px;"" />
 
 При вычислении массы формулы ионного соединения использовались средние массы нейтральных атомов натрия и хлора, а не массы для катионов натрия и анионов хлорида. Даже если катион натрия имеет немного меньшую массу, чем атом натрия (так как в нем отсутствует электрон), эта разница будет компенсирована тем, что анион хлорида чуть более тяжёлый, чем атом хлора (из-за дополнительного электрона). Более того, масса электрона пренебрежимо мала по отношению к массе типичного атома. 
 
 <h4>Массовый процентный состав </h4>
 
 Элементный состав вещества определяет его химическую идентичность, а химические формулы являются наиболее точным способом представления этого элементного состава. Процент по массе каждого элемента в составе вещества называется процентом массы этого конкретного элемента. Процентное соотношение можно рассчитать, разделив массу каждого элемента на общую массу вещества, а затем преобразовать в процент. 
 
 Процентный состав полезен для оценки относительного содержания данного элемента в различных соединениях известных формул. Коль скоро известна молекулярная или эмпирическая формула вещества, состав в процентах может быть получен из атомных или молярных масс элементов соединения.  
 
 Например, одна молекула азотной кислоты (HNО3) содержит один атом азота весом 14.01 amu, один атом водорода весом 1.008 amu и три атома кислорода весом (3 × 16.00 amu) = 48.00 amu. Формула массы азотной кислоты поэтому (14.01 amu + 1.008 аму + 48.00 amu) = 63.02 аму, и это процентное соотношение составляет: 
 
 <img alt=""Eq3"" src=""https://www.jove.com/files/core/CDNSource/lessons/1017/1017_Equations-03.png"" style=""height: 40px;"" />
 
 <img alt=""Eq4"" src=""https://www.jove.com/files/core/CDNSource/lessons/1017/1017_Equations-04.png"" style=""height: 40px;"" />
 
 <img alt=""Eq5"" src=""https://www.jove.com/files/core/CDNSource/lessons/1017/1017_Equations-05.png"" style=""height: 40px;"" />
 
 Этот текст адаптирован из <a href=""https://openstax.org/books/chemistry-2e/pages/3-1-formula-mass-and-the-mole-concept"">Openstax, Химия 2е изд., раздел 3.1: Formula Mass и Mole Concept</a> и <a href=""https://openstax.org/books/chemistry-2e/pages/3-2-determining-empirical-and-molecular-formulas"">Openstax, Химия 2е изд., раздел 3.2: Определение эмпирических и молекулярных формул.</a>"

Формула массы ковалентных соединений

Химические формулы представляют собой элементный состав веществ. Для ковалентных соединений формула представляет собой ...

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chemical formula mass and percent composition

Chemical formula mass and percent composition help describe the makeup of compounds. A chemical formula shows which atoms are present and how many of each atom appear in a substance.

For covalent compounds, the formula shows the atoms in one molecule. That is why formula mass can also be called molecular mass. Chloroform, CHCl3, is one example. Its formula shows one carbon atom, one hydrogen atom, and three chlorine atoms. The molecular mass is the sum of their average atomic masses.

Ionic compounds are different because they contain cations and anions that combine in ratios that make the bulk material electrically neutral. Their formula mass is found the same way, by adding the average atomic masses of the atoms in the formula. Sodium chloride, or table salt, is one example. Its formula, NaCl, shows sodium and chloride in a 1:1 ratio. For ionic compounds, the term molecular mass is not the best choice because the formula does not describe a single molecule.

When calculating formula mass for an ionic compound, neutral atom masses are used instead of ion masses. A sodium cation has slightly less mass than a sodium atom because it has lost an electron. A chloride anion has slightly more mass than a chlorine atom because it has gained an electron. The difference is small, and the mass of an electron is negligibly small compared with the mass of a typical atom.

Percent composition tells how much of a compound’s mass comes from each element. It is found by dividing the mass of each element by the total mass of the compound and converting the result to a percentage. This is useful for comparing the relative amount of an element in compounds with known formulas.

Nitric acid, HNO3, shows how the calculation works. One molecule contains one nitrogen atom with a mass of 14.01 amu, one hydrogen atom with a mass of 1.008 amu, and three oxygen atoms with a total mass of 48.00 amu. Its formula mass is 63.02 amu. From that total, the percent composition of each element can be determined.

Chemical Formula Mass and Percent Composition

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formula mass and mole concepts of compounds

Chemical formula mass and percent composition help describe the makeup of compounds. A chemical formula shows which atoms are present and how many of each atom appear in a substance. For covalent compounds, the formula shows the atoms in one molecule. That is why formula mass can also be called molecular mass. Chloroform, CHCl3, is one example. Its formula shows one carbon atom, one hydrogen atom, and three chlorine atoms. The molecular mass is the sum of their average atomic masses. Ionic...

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Learn how to calculate formula mass for covalent and ionic compounds, then use it to find percent composition with examples like chloroform, salt, and nitric acid.

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Chemical Formula Mass and Percent Composition

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