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How to calculate molar mass


How to calculate molar mass

The masses of atoms or molecules are extremely small,Therefore, in molecular physics, instead of the very masses of molecules and atoms, it is prudent to use, on Dalton's suggestion, their relative magnitudes, comparing the mass of a molecule or atom with 1/12 part of the mass of a carbon atom.

The amount of a substance that contains as many molecules or atoms as they contain in 12 grams of carbon is called a mole. The molar mass of the substance (M) is the mass of one mole.

The molar mass is a scalar quantity, measured in the international SI system in kilograms divided by mole.



To calculate the molar Bulk It is sufficient to know two quantities: Bulk Substance (m), expressed in kilograms, and the amount of substance (v) measured in moles, substituting them into the formula: M = m / v.
Example. Let it be necessary to determine the molar Bulk 100 g of water in 3 moles. To do this, first translate Bulk Water in from grams to kilograms - 100g = 0.01kg. Then substitute the values ​​in the formula for calculating the molar mass: M = m / v = 0.01 kg / 3 mol = 0.003 kg / mol.


If the equation M = m /? Substitute another known identity:? = N / Nа, where N is the number of molecules or atoms of the substance, Na is the Avogadro constant, equal to 6 * 10 to 23 degrees, then the molar mass is calculated by another formula: M = m0 * Nа. That is, there is one more formula for calculating the molar mass.
Example 2. The mass of a molecule of matter is 3 * 10 (minus 27 degrees) kg. Find Molar Bulk Substance. Knowing the value of Avogadro's constant number, solve the formula: M = 3 * 10 (minus 27 degrees) kg * 6 * 10 (to 23 degrees) 1 / mol = 18 * 10 (minus 4 degrees) kg / mole.

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