you need
  • - Periodic Table of Elements DIMendeleev
Guide
1
In order to calculate the proportion mass , you must first find the relative atomic mass (Ar) of the desired item , and the relative molecular mass (Mr) substances.Next, apply the formula by which determine the mass fraction
element (W) W = Ar (x) / Mr x 100% in kotoroyW - mass fraction element (measured in fractions or%); Ar (x) - Relativethe atomic mass of the element ; Mr - relative molecular mass veschestva.Dlya determine the relative atomic and molecular masses, use of the periodic table of chemical elements DIMendeleev.In the calculations required to take into account the number of atoms of each element .
2
Example № 1. Determine the mass fraction of hydrogen vode.Naydite the table D.Mendeleyev relative atomic mass vodorodaAr (H) = 1. Since the formula 2 hydrogen atoms, hence, 2Ar (H) = 1 x = 2 2Vychislite relative molecular weight of water (H2O), which consists of 2 Ar (H) and Ar 1(O) .Mr (H2O) = 2Ar (H) + Ar (O) Ar (O) = 16, sledovatelnoMr (H2O) = 1 x 2 + 16 = 18
3
Record general formula definitionmass fraction element W = Ar (x) / Mr x 100% Now write the formula for the conditions zadachiW (H) = 2 Ar (H) / Mr (H2O) x 100% Make vychisleniyaW (H) = 2/18x 100% = 11,1%
4
Example № 2. Determine the mass fraction of oxygen copper sulfate (CuSO4) Analyzed by Table D.Mendeleyev kislorodaAr relative atomic mass (O) = 16. Since the formula 4 oxygen atoms, therefore Ar 4 (D) = 4 x 16 = 64Vychislite relative molecular mass of copper sulfate (CuSO4), which consists of 1 Ar (Cu),1 Ar (S) 4 and Ar (O) .Mr (CuSO4) = Ar (Cu) + Ar (S) + 4 Ar (O) .Ar (Cu) 64 = Ar (S) = 324 Ar (O) =4 x 16 = 64, sledovatelnoMr (CuSO4) = 64 + 32 + 64 = 160
5
Write down the general formula for determination of element W = Ar (x) / Mr x 100% Now, write down the formulaas applied to the condition zadachiW (G) = 4 Ar (O) / Mr (CuSO4) x 100% Make vychisleniyaW (O) = 64/160 x 100% = 40%