In Chemistry, mole concept is an important topic that finds application right from high school up to research level studies. One often reads in chemistry book that two moles of hydrogen reacts with one mole of oxygen to yield two moles of water. In every balanced chemical equation, mole concept plays a fundamental role in determining the nature and quantity of these reactions. Therefore, mole concept is a topic that can never be overlooked in the study of chemistry. With this background, let us try and understand this interesting concept.
In simplest terms, a mole is defined as a unit of measurement. It is basically utilized to measure the amount of any molecule, ion or atom (also termed as fundamental entity) that is found in a substance. It can be also assumed to be an analogous of weight, because both these terms of mole and weight are fundamentally addressed at determining the total amount of a substance that is produced or present or used. The term ‘mole’ was first coined by a German scientist by the name of Wilhelm Ostwald in the year of 1896. If one was to look at the origins of the word ‘mole’ then it is found that it is rooted in Latin, where it means ‘a pile’. At the initial stages of its inception, the term mole was a relative unit with the mass of carbon being used as the base reference unit. Visit Here: gopage7
To be precise, it was defined to be the amount of substance containing the equal number of atoms, ions or molecules as the number of atoms found in a pure sample of carbon that weighed exactly 12 grams. However, with research and development of science, the definition of mole has been changed. It is now based on the Avogadro’s constant. Thus, a mole is defined to contain a total of 6.022 x 1023 units of fundamental entities such as ions, atoms or molecules. This constant is popularly known as the Avogadro’s number. One must bear in mind that when one says that two moles of hydrogen reacts with one mole of oxygen to yield two moles of water, then it can be read as follows,
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- there are twice the Avogadro’s number of hydrogen atoms reacting with 6.022 x 1023 (Avogadro constant) number of atoms of oxygen to yield two times the Avogadro number of atoms of water.
As one can see, the number of fundamental entities remains fixed for one mole, however this is not true for the molar mass of these reactants or products. Therefore, one mole of hydrogen does not have the same molar mass as one mole of oxygen or water. This can be explained from the fact that although the number of atoms remains fixed, the size of atoms vary in size as well as mass. Visit Here: wmt24
There are important terms that must be remembered by students when studying the mole concept. These terms are mentioned below,
- Molar Mass – This is defined as the mass of one mole of a substance, and it is not the same as molecular mass of the same substance. Its SI unit is kg/mol
- Molecular Mass – This is defined as the mass of a molecule, which in turn is the addition of the masses of every individual constituent element of the molecule.
- Atomic Mass Unit – This is also written as A.M.U. It is defined as the ratio of mass of the substance to Avogadro’s number. One important point to bear in mind is that 1 mol is always equal to its corresponding atomic mass unit.visit here to know more information : msizone
In any given pure sample, the total number of moles of the substance under consideration is determined as the ratio of the total number of fundamental entities present in the sample to the Avogadro’s constant.
Let us solve a few numerical problems to gain more insight into the mole concept. Let us take the example of one mole of Hydrogen molecule (H2) and determine the total number of electrons present in it.
As stated above, one more of any substance will have 6.022 x 10^23 fundamental entities. Each mole of hydrogen contains 2 electrons, therefore, the total number of electrons in one mole of hydrogen is 2 x Avogadro’s Number, i.e, 12.044 x 10^23 electrons.
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Let us take another problem and determine the number of mole present in a litre of water. This can be solved by knowing that the density of water at standard temperature and pressure is 1gm per cubic centimetre. This signifies that 1cc of water has a mass of 1 gram. Also, from definitions we have learnt that one mole is equal to 1 A.M.U of the substance, i.e. water in our case. Therefore, knowing the atomic mass of hydrogen and oxygen, we can determine that 1 mole=18g of water = 18 cc of water.
Thus, 1 cc of water is 0.055 moles. We know 1 litre of water is equal to 1000 cc, therefore, in one litre of water, there are 0.055 x 1000 = 55 moles of water. Visit Here: eblogz
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