Mole Concept Of Class 11
Beverly Friddle
Mole concept is known as the method used to express the amount of substance. A mole is defined as the amount of substance containing the same number of different entities (such as atoms, ions, and molecules) as the number of atoms in a sample of pure 12C weighing precisely 12 g. Even a gram of any pure element contains a high amount of atoms. The mole connects a simple macroscopic feature (bulk mass) to a genuinely significant fundamental trait (number of atoms, molecules, etc.). One mole is also defined as the amount of a substance that contains as many entities as there are atoms in exactly 12 g of the 12C isotope. It was found that the mass of one atom of carbon-12 element is equal to 1.992648 10-23 g as measured by the mass spectrometer. Since one mole of Carbon-12 atom weighs 12 g, therefore, the number of atoms in it equals 12 g mol-1 / 1.992648 1023 g atom-1 = 6.0221367 1023 atoms mol-1. The following formula may be used to calculate the number of moles of a chemical in a given pure sample:
Atomic mass of an element is the mass of its one atom. The unit of atomic mass is a.m.u. The atomic mass is roughly the sum of protons and neutrons present in the atom. One atomic mass unit (a.m.u.) is said to be exactly equal to one-twelfth the mass of one carbon-12 atom. Therefore, the value of one a.m.u. is 1 g / NA = 1.66056 10-24 g. In the present era, the atomic mass unit is known as a unified mass unit. Hence, a.m.u. has been replaced by u.
For example, the atomic mass of carbon is 12.011 amu since carbon mostly contains carbon-12 isotope. Carbon-13 is 1.1%, and very few traces of carbon-13. The atomic mass of these isotopes is different.
Gram atomic mass is the mass of one mole of an atom. Gram molecular mass is the mass of one mole of a molecular substance expressed in grams. It is also known as molar mass. It is also defined as the mass of one mole of molecules. This is the difference between gram atomic and gram molecular mass. This amount of a substance is also called one gram molecule.
The volume occupied by one gram mole of a substance in a vapor state or gaseous state at STP is called as gram molecular volume. The standard temperature to obtain GMV is 273K, and the standard pressure is 1 atm. The ideal gas equation is utilized to get gram molar volume (GMV = 22.4L).
Relative molecular mass is the molecular weight of an element or molecule; it is expressed as RMM. It is the number of times a single molecule of a substance remains heavier than one-twelfth the mass of a carbon atom (12C).
Mole fraction is defined as the number of single component molecules divided by the total number of molecules. When two reactive elements are combined together, the ratio of the two elements is understood by the mole fraction.
Mole concept provides a standard for measuring certain masses that are universally accepted. It provides a link between several masses and is an efficient way to measure macroscopic properties. For the study of chemistry, understanding mole concept is essential, and knowledge of how mole is applied to masses, number of substances, etc., is important.
The mole concept is central to any chemistry calculation based on experimental results. The mole is how we relate the unbelievably small atoms and molecules that make something up to the measurable properties such as mass which we may observe in a laboratory setting. A proper understanding of the mole concept is essential in order to do any calculations on experimental data. The mole concept is introduced in this chapter, and will appear again in many of the forthcoming chapters. Mastering the concepts in those later chapters is dependent upon mastering the mole concept in this chapter. This might be the most important chapter in the textbook!
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Question 28.
Calculate approximately the diameter of an atom of mercury, assuming that each atom is occupying a cube of edge length equal to the diameter of the mercury atom. The density of mercury is 13.6 g/cc.
Question 31.
It is found that in 11.2 liters of any gaseous compound of phosphorus at NTP, there is never less than 15.5 g of P. Also, this volume of the vapour of phosphorus itself at NTP weighs 62 g. What should be the atomic mass and molecular mass of the phosphorus?
Question 33.
It has been estimated that 93% of all atoms in the entire universe are hydrogen and that the vast majority of those remaining are helium. Based on only these two elements, estimate the mass percentage composition of the universe.
Question 35.
At room temperature, the density if water is 1.0 g/mL and the density of ethanol is 0.789g/mL. What volume of ethanol contains the same number of molecules as are present in 175 mL of water?
The above problems are good but if some more solved problems would be available then i could cope with the topic of mole concept.i feel this topic is quite difficult for me,so iwant some more sums on this concept
The study of atoms and its related traits lay the foundation for chemistry. Atomic mass is the concept related to a single atom, whereas molecular mass relates to a group of atoms. If you are planning to proceed with this concept, then it is necessary to gain precise knowledge about molecular mass and mole concept. Let us proceed!
You can call the molecular mass of a substance as the relative mass of its molecule when compared with the mass of 12C atom considered as 12-units. In simple terms, it points out the number of times; 1 molecule of the concerned substance is weightier than an atom.
RMM or Relative molecular mass is the molecular weight of an element or compound. You can call it as the number of times a single molecule of the substance stays heavier than the 1/12th mass of carbon atom (12C).
But, the same traits were previously derived from the evaluation of macroscopic properties using comparatively simple tools. Such an experimental approach did require the introduction of a fresh unit for defining the quantity of substances, called as the mole.
It is interesting to know that, to date, this unit stays essential for modern chemical science. What is a mole? It is an amount unit that can be seen similar to familiar units such as a pair, gross, dozen etc. To be precise, it offers a specific measure of the count of atoms or molecules present in a sample bulk matter.
Furthermore, a mole can be defined as the quantity of substance comprising the same number of distinct entities (like atoms, ions, and molecules) as the count of atoms in a sample comprising pure 12C weighing accurately 12 g. The mole offers a link between a simply calculated macroscopic property (bulk mass) and a truly significant fundamental property (number of atoms, molecules etc.).
The mole (symbol mol) is a unit of measurement, the base unit in the International System of Units (SI) for amount of substance, a quantity proportional to the number of elementary entities of a substance. One mole contains exactly 6.022140761023 elementary entities (approximately 602 sextillion or 602 billion times a trillion), which can be atoms, molecules, ions, or other particles. The number of particles in a mole is the Avogadro number (symbol N0) and the numerical value of the Avogadro constant (symbol NA) expressed in mol-1.[1] The value was chosen based on the historical definition of the mole as the amount of substance that corresponds to the number of atoms in 12 grams of 12C,[1] which made the mass of a mole of a compound expressed in grams, numerically equal to the average molecular mass of the compound expressed in daltons. With the 2019 redefinition of the SI base units, the numerical equivalence is now only approximate but may be assumed for all practical purposes.
Depending on the nature of the substance, an elementary entity may be an atom, a molecule, an ion, an ion pair, or a subatomic particle such as a proton. For example, 10 moles of water (a chemical compound) and 10 moles of mercury (a chemical element) contain equal numbers of substance, with one atom of mercury for each molecule of water, despite the two quantities having different volumes and different masses.
The mole corresponds to a given count of entities.[5] Usually the entities counted are chemically identical and individually distinct. For example, a solution may contain a certain number of dissolved molecules that are more or less independent of each other. However, in a solid the constituent entities are fixed and bound in a lattice arrangement, yet they may be separable without losing their chemical identity. Thus the solid is composed of a certain number of moles of such entities. In yet other cases, such as diamond, where the entire crystal is essentially a single molecule, the mole is still used to express the number of atoms bound together, rather than a count of molecules. Thus, common chemical conventions apply to the definition of the constituent entities of a substance, in other cases exact definitions may be specified.The mass of a substance is equal to its relative atomic (or molecular) mass multiplied by the molar mass constant, which is almost exactly 1 g/mol.
The name mole is an 1897 translation of the German unit Mol, coined by the chemist Wilhelm Ostwald in 1894 from the German word Molekl (molecule).[6][7][8] The related concept of equivalent mass had been in use at least a century earlier.[9]
The oxygen-16 definition was replaced with one based on carbon-12 during the 1960s. The mole was defined by International Bureau of Weights and Measures as "the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12." Thus, by that definition, one mole of pure 12C had a mass of exactly 12 g.[11][5] The four different definitions were equivalent to within 1%.
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