Calculate the relative molecular weights, molar masses, and mass fraction of each element

| July 28, 2021 | education

Calculate the relative molecular weights, molar masses, and mass fraction of each element in a molecule of water, carbon dioxide, sodium chloride, sulfuric acid, and limestone.

To determine the relative molecular mass of a substance Mr, it is necessary to add the relative atomic masses of the elements that make up the compound, multiplying by the indices at the elements. The molar mass is numerically equal to Mr, but shows how much a mole of a substance weighs and is measured in g / mol.

Mr (H2O) = 2 * Ar (H) + Ar (O) = 2 + 16 = 18 amu. eat.

M (H2O) = 18 g / mol.

w (H) = 2/18 * 100% = 11.1%

w (O) = 16/18 * 100% = 88.9%

Mr (CO2) = Ar (C) + 2 * Ar (O) = 12 + 2 * 16 = 44 amu. eat.

M (CO2) = 44 g / mol.

w (C) = 12/44 * 100% = 27.3%

w (O) = 16 * 2/44 * 100% = 72.7%

Mr (NaCl) = Ar (Na) + Ar (Cl) = 23 + 35.5 = 58.5 a. eat.

M (NaCl) = 58.5 g / mol.

w (Na) = 23 / 58.5 * 100% = 39.3%

w (Cl) = 35.5 / 58.5 * 100% = 60.7%

Mr (H2SO4) = 2 * Ar (H) + Ar (S) + 4 * Ar (O) = 2 + 32 + 4 * 16 = 98 amu. eat.

M (H2SO4) = 98 g / mol.

w (H) = 2/98 * 100% = 2.0%

w (S) = 32/98 * 100% = 32.7%

w (O) = 64/98 * 100% = 65.3%

Mr (CaCO3) = Ar (Ca) + Ar (C) + 3 * Ar (O) = 40 + 12 + 3 * 16 = 100 amu. eat.

M (CaCO3) = 100 g / mol.

w (Ca) = 40/100 * 100% = 40.0%

w (C) = 12/100 * 100% = 12.0%

w (O) = 48/100 * 100% = 48.0%



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