The chemical formula of a compound is a symbolic representation of its chemical composition. Chemical formulae provide insight into the elements that constitute the molecules of a compound and also the ratio in which the atoms of these elements combine to form such molecules.
For example, the chemical formula of water, which is H2O, suggests that two hydrogen atoms combine with one oxygen atom to form one molecule of water.
While the term ‘chemical formula’ typically refers to the molecular formula of a compound (which denotes the total number of atoms of each constituent element in one molecule of the compound), the compositions of chemical compounds can be expressed in several ways, as listed in this subsection.
In order to write a chemical formula, it is important to know the symbol of the elements present in the compound, formula of the radicals and the valency of the elements in that compound. Following points should be kept in mind while writing a chemical formula.
Problem 1: In one molecule of the compound, determine how many atoms of every element are present for each one of these chemical formulas.
Therefore, the mass of one mole of an element will be equal to its atomic mass in grams.
Formulas of Mole Concept
Some solved example questions on the mole concept are provided in this subsection.
Q.1: How many moles of iron are present in a pure sample weighing 558.45 grams?
Ans: The molar mass of iron is 55.845 g/mol. Therefore, the number of moles of iron in the pure sample weighing 558.45 grams is: = 10 moles.
Q.2: How many molecules of water are present in 36 grams of water?
Ans: The molar mass of water is 18 (approximately). Therefore, 36 grams of water makes up a total of 2 moles. Each mole has 6.022*1023 water molecules. The total number of H2O molecules in 36 grams of water is: 12.044*1023
Q.3: How many grams of carbon can be found in 1 mole of carbon dioxide?
Ans: 1 mole of CO2 contains 1 mole of carbon and 2 moles of oxygen. The molar mass of carbon is 12.0107 g/mol. Therefore, 1 mole of CO2 contains 12.01 grams of carbon and 32 grams of oxygen.
Q. What is a mole equal to?
Ans: One mole of a substance is equal to the substance’s 6.022 x 1023 units (such as atoms, molecules, or ions). The 6.022 x 1023 number is known as the number of Avogadro or the constant of Avogadro. For the conversion of mass and number of particles, the definition of the mole can be used.
Q. What is the importance of the mole concept?
Ans: All chemistry is pervaded by the mole definition. Since most quantitative chemical calculations are focused on the mole, for the study of chemistry, an understanding of the mole is important. A knowledge of how the mole applies to mass, number of entities
Q. What is a mole in chemistry?
Ans: In chemistry, the mole, also written mol., is a standard scientific unit for the calculation of large amounts of very small entities, such as atoms, molecules, or other objects.
Q. Why do we use mole fraction?
Ans: The mole fraction defines the number of single component molecules (or moles) divided by the total number of molecules (or moles) in the mixture. When two reactive components are mixed together, the mole fraction is useful, as the ratio of the two components is understood if the mole fraction of each is known.
Q. Is mole fraction equal to partial pressure?
Ans: In a mixture, the partial pressure of each gas is proportional to the mole fraction. The pressure exerted by each gas (its partial pressure) in the gas mixture is independent of the pressure exerted by all other gases present in the gas mixture.
What is the Mole Concept?
The mole concept is a convenient method of expressing the amount of a substance. Any measurement can be broken down into two parts – the numerical magnitude and the units that the magnitude is expressed in. For example, when the mass of a ball is measured to be 2 kilograms, the magnitude is ‘2’ and the unit is ‘kilogram’.
When dealing with particles at an atomic (or molecular) level, even one gram of a pure element is known to contain a huge number of atoms. This is where the mole concept is widely used. It primarily focuses on the unit known as a ‘mole’, which is a count of a very large number of particles.
What is a Mole?
In the field of chemistry, a mole is defined as the amount of a substance that contains exactly 6.02214076 * 1023 ‘elementary entities’ of the given substance.
The number 6.02214076*1023 is popularly known as the Avogadro constant and is often denoted by the symbol ‘NA’. The elementary entities that can be represented in moles can be atoms, molecules, monoatomic/polyatomic ions, and other particles (such as electrons).
For example, one mole of a pure carbon-12 (12C) sample will have a mass of exactly 12 grams and will contain 6.02214076*1023 (NA) number of 12C atoms. The number of moles of a substance in a given pure sample can be represented by the following formula:
n = N/NA
Where n is the number of moles of the substance (or elementary entity), N is the total number of elementary entities in the sample, and NA is the Avogadro constant.
The word “mole” was introduced around the year 1896 by the German chemist Wilhelm Ostwald, who derived the term from the Latin word moles meaning a ‘heap’ or ‘pile.
The number of moles of a molecule may not always be equal to the number of moles of its constituent elements. For example, a mole of water contains NA number of H2O molecules. However, each water molecule contains 2 hydrogen atoms and one oxygen atom. Therefore, one mole of H2O contains 2 moles of hydrogen and one mole of oxygen.
|1. What is the chemical formula for water?
|2. What is the chemical formula for table salt?
|3. What is the chemical formula for carbon dioxide?
|4. How is the chemical formula of a compound determined?
|5. What is the significance of the chemical formula in understanding a compound?