Name: chemical formula mass and percent composition
Uploaded: 2020-09-03T13:38:26.000Z
Duration: 2 min 56 s
Channel: JoVE

K12 Standards

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NC K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.3.3

formula-mass-and-mole-concepts-of-compounds

Formula Mass and Mole Concepts of Compounds

化合物の最小の代表単位は 化学式で表される分子 または式単位です 化学式に含まれる すべての原子の原子質量を足すと その化合物の分子質量 または式の質量が得られ 原子質量単位で算出されます 例えば ショ糖や食卓糖の 分子量を求めるには 各元素の 原子質量に対応する元素の 原子数を掛け合わせます 合計は ショ糖の分子量を示します 化合物の1モル中に存在する すべての分子または式単位の 質量はモル質量と呼ばれ 1モルあたりのグラムで 測定されます 化合物のモル質量は 数値的にはその 分子質量または式質量と 等しくなります 例えば 分子量342.3 原子質量単位のショ糖は モル当たり342.3グラムの モル質量を 持つことになります 化学物質中に存在する 分子や粒子の 実際の数を知ることは その組成 相互作用 および 組み合わせを理解するための 基本的なことです しかし 通常の方法では ある化合物サンプルの 実際の分子数を数えることは できません そこで モル質量 モル数 アボガドロ数の 関係を利用することで 存在する総分子数を 計算することができます この考え方によれば 化合物のモル質量は 化合物の1モルに相当し 6.022×10^23個の 粒子を構成しています 342.3グラムのショ糖には 6.022×10^23個の ショ糖分子が 含まれていることになります しかし ショ糖試料の重量が 例えば150グラム と分かれば クロスマルチプル法を 用いた計算で 分子数を求めることができます その結果150グラムのショ糖が 2.63×10^23のショ糖分子を 構成していることがわかります 化合物中の各元素の割合は 質量パーセント値を使用して 表すことができます 計算するには 化合物の1モル中の 元素の質量を化合物の 1モルの総質量で割ることで パーセンテージに変換されます 実際には ショ糖中の 水素の質量％を計算するために ショ糖分子の総質量と 水素原子の総質量が 式に含まれています 計算された値はショ糖が 6.4質量％の水素を 含むことを示しています

化合物の質量とモルの概念

<h4>共有結合化合物の分子量 </h4>
 
 化学式は物質の元素構成を表すものです。 共有結合化合物の場合、その物質の１つの分子を構成する原子の数と種類を式で表します。したがって、式の質量は分子の質量と呼ぶのが正しい場合があります。 共有結合化合物であるクロロホルム（ CHCl3 ）の分子式は、 1 つの分子の中に 1 つの炭素原子、 1 つの水素原子、および 3 つの塩素原子が含まれていることを示しています。 クロロホルム分子の平均分子質量は、これらの原子の平均原子質量の合計と等しくなります。 
 
 <img alt="Eq1" src="https://www.jovecore.com/CDNSource/lessons/1017/1017_Equations-01.png" style="height: 40px;" />
 
 <h4>イオン化合物の分子量 </h4>
 
 イオン化合物は、個別の陽イオンと陰イオンが、電気的に中性のバルク物質になるような比率で結合しています。 イオン化合物の式質量は、共有結合化合物の式質量と同じ方法で計算されます。つまり、化合物の式に含まれるすべての原子の平均原子質量を合計します。 ただし、イオン化合物の式は個別の分子の組成を表すものではないため、正しくは「分子質量」と呼べない場合があります。 
 
 たとえば、一般的な食卓塩または塩化ナトリウム（ NaCl ）は、ナトリウムイオン（ Na+ ）と塩化物イオン（ Cl −）を 1 ： 1 の比率で混合したイオン化合物です。 この化合物の分子量は、その構成元素の平均原子質量を加えて算出されます。 
 
 <img alt="Eq2" src="https://www.jovecore.com/CDNSource/lessons/1017/1017_Equations-02.png" style="height: 40px;" />
 
 イオン化合物の分子量を計算する際には、ナトリウムイオンおよび塩化物イオンの質量ではなく、中性のナトリウムおよび塩素原子の平均質量が使用されます。 ナトリウムイオンの質量はナトリウム原子よりもわずかに小さくなるが（電子が１個ないので）、この差は、塩化物イオンの質量が塩素原子よりもわずかに大きい（余分な電子があるため）という事実によって相殺されます。 さらに、電子の質量は一般的な原子の質量に対して無視できるほど小さいです。 
 
 <h4>質量パーセント組成 </h4>
 
 化合物の元素構成はその化学的性質を定義し、化学式はこの元素構成を最も簡潔に表したものです。 化合物内中の各元素の質量に対する割合を、その元素の質量パーセントと呼びます。 パーセント組成は、各元素の質量を化合物の総質量で割って算出し、パーセントに換算します。 
 
 パーセント組成は、既知の式のさまざまな化合物に含まれる、特定の元素の相対的な存在量を評価するのに役立ちます。 対象となる化合物の分子式または経験式がわかっている限り、パーセント組成は化合物の元素の原子質量またはモル質量から導出できます。  
 
 例えば、硝酸（ HNO3 ） 1 分子には、重さが 14.01 amu の窒素原子 1 個、1.008 amu の水素原子 1 個、および重さが 3 × 16.00 amu の酸素原子 3 個、 48.00 amu 含まれています。 従って硝酸の公式の質量は (14.01 amu + 1.008 amu + 48.00 amu) = 63.02 amu であり、パーセントの組成は : 
 
 <img alt="Eq3" src="https://www.jovecore.com/CDNSource/lessons/1017/1017_Equations-03.png" style="height: 40px;" />
 
 <img alt="Eq4" src="https://www.jovecore.com/CDNSource/lessons/1017/1017_Equations-04.png" style="height: 40px;" />
 
 <img alt="Eq5" src="https://www.jovecore.com/CDNSource/lessons/1017/1017_Equations-05.png" style="height: 40px;" />
 
 このテキストは <a href="https://openstax.org/books/chemistry-2e/pages/3-1-formula-mass-and-the-mole-concept">、 Openstax 、 Chemistry 2e 、 Section 3.1 ： Formula Mass and the Mole Concept</a> and <a href="https://openstax.org/books/chemistry-2e/pages/3-2-determining-empirical-and-molecular-formulas">Openstax 、 Chemistry 2e 、 Section 3.2 ： Determining Empirical and Molecular Formulas から引用しています。</a>

共有化合物の式質量

化学式は、物質の元素構成を表しています。共有結合性化合物の場合、式は...

Education

JoVE Core

化学

Molecules, Compounds, and Chemical Equations

分子、化合物、および化学方程式

molecules-compounds-and-chemical-equations

KEY TERMS AND CONCEPTS

主要用語と概念

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

chemical-formula-mass-and-percent-composition

molecules and compounds

Atomic Elements, Molecules, and Bonds

Matter is made of elements, and elements are built from atoms. An atom is the smallest unit of an element that still keeps that element’s properties. A silver coin, for example, is made of silver atoms. Each atom keeps the unique properties of silver. Elements are pure substances made of identical atoms. They cannot be broken down into simpler substances by chemical changes. Most elements are atomic elements, which use single atoms as their basic unit. Carbon and sodium are examples of atomic...

molecular models

Molecular Model Types in Chemistry

Molecular models help chemists and students visualize the structures and shapes of atoms and molecules. They represent the molecular architecture of chemical compounds in a way that is easier to study than formulas alone. Skeletal models are simple two-dimensional drawings of compounds. They show the molecular framework, or the bonds, without drawing every atom. In this model, many carbon and hydrogen atoms are not shown directly. Their positions are implied by the ends and junctions of the...

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Organic Molecules in Everyday Chemistry

Organic molecules are carbon-based compounds found in living things and in many everyday products. Most organic compounds have carbon as the main element, bonded to hydrogen and other carbon atoms. Some carbon-containing substances, such as carbonates, cyanides, and simple oxides like CO and CO2, are not classified as organic. Carbon can form up to four strong bonds, which helps explain why organic compounds can make chains and rings of many sizes and shapes. These molecules appear in...

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...

experimental determination of chemical formula

experimental-determination-of-chemical-formula

Finding Empirical and Molecular Formulas

Chemical formulas show the elemental makeup of a compound. When a formula is unknown, scientists often start by measuring the masses of the elements in the sample. Those mass data are then used to find the simplest whole-number ratio of atoms, which gives the empirical formula. To get from mass to atom ratio, the masses of the elements are first converted to moles using molar masses. Chemical formulas describe numbers of atoms, not masses, so this step is necessary. In one example, 1.71 grams...

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Chemical equations show the identities and relative amounts of substances in a chemical reaction. The substances that react are called reactants, and their formulas are written on the left side of the equation. The substances formed are called products, and their formulas are written on the right side. A plus sign (+) separates formulas on the same side, and an arrow (→) shows the change from reactants to products. The numbers in a chemical equation are shown with coefficients. A coefficient...

key terms and concepts

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.

Chemical Formula Mass and Percent Composition | JoVE K12

chemistry

JoVE Core 化学は、簡潔で理解しやすいアニメーションビデオレッスンを使用して、一般的な化学の概念を生き生きとしたものにします。さらに、活動する科学者のビデオでは、現在世界中の実験室で行われている古典的そして独創的な研究・実験をお見せします。

PS.Chm.4.3

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Ohio’s Learning Standards and Model Curriculum

Structure And Properties Of Matter

Quantifying matter

Interactions Of Matter

Stoichiometry

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CHEM1.PS1.3

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HIgh School

CH.3

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Florida Department of Education

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New York State Science Learning Standards

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Georgia Standards of Excellence

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The Mole Concept and Avogadro’s Number

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PS.Chm.3.1

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PS.Chm.3.2

Analyze the structure of atoms and isotopes.

Chemical Formula Mass and Percent Composition

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