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How to calculate the molar mass

How to calculate the molar mass

The masses of atoms or molecules are extremely small,therefore in molecular physics instead of the masses of molecules and atoms prnyato use on a proposal from Dalton their relative values ​​by comparing the mass of the atom or molecule with a 1/12 part of the mass of a carbon atom.

The amount of substance which contains the same number of atoms or molecules, as they contain 12 grams of carbon, called mole. The molar mass of a substance (M) - is the mass of one mole.

Molar mass - the value of a scalar, it is measured in the international SI system in kilogammah divided by moles.

instructions

1

To calculate the molar weight enough to know two values: weight substance (m), expressed in kilograms, and the amount of substance and (v), measured in moles, substituting them into the formula: M = m / v.
Example. Suppose that it is necessary to determine the molar weight 100 g of water of 3 moles. To do this, you must first translate weight water from grams to kilograms - 100g = 0,01kg. Then substitute the values ​​into the formula to calculate the molar mass M = m / v = 0,01kg / 3 mol = 0,003kg / mol.

2

If the equation M = m /? substitute other known identity:? = N / Na, where N-number of molecules or atoms of the substance, Na- Avogadro constant equal to 6 * 10 to 23 degrees, the molar mass is calculated by another formula: M = m0 * Na. That is, there is another formula for calculating the molar mass.
Example 2. The weight molecules of the substance is 3 * 10 (minus 27 degrees) kg. Find molar weight substance. Knowing the value of the Avogadro constant number, to solve the formula: M = 3 x 10 (minus 27 degrees) kg * 6 * 10 (23 degree) 1 / mol = 18 * 10 (minus 4 degrees) kg / mol.

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