You will need

- - the periodic system of chemical elements D. I. Mendeleev

Instruction

1

In order to calculate the mass

*fraction*, you must first find the relative atomic mass (Ar) of the desired**element**, and the relative molecular mass (Mr) of the substance. Next, apply the formula, which is determined and the mass fraction**of the element**(W)W = Ar (x) / Mr x 100 %, которойW - mass fraction**of the element**(measured in fraction or %);Ar (x) is the relative atomic mass**of element**;Mr is the relative molecular mass of the substance.To determine the relative atomic and molecular masses, use the periodic system of chemical elements D. I. Mendeleev. The calculations take into account the number of atoms of each**element**.2

Example No. 1. Determine the mass

*fraction*of hydrogen in water.Look at the table of D. I. Mendeleev of the relative atomic mass of vodoroda (H) = 1. As in formula 2 of the hydrogen atom, therefore, 2Ar (H) = 1 x 2 = 2Вычислите the relative molecular mass of water (H2O), which consists of 2 Ar (H) and 1 Ar (O).Mr (H2O) = 2Ar (H) + Ar (O)Ar (O) = 16, sledovatelno (H2O) = 1 x 2 + 16 = 183

Write down a General formula for determining the mass fraction

**of the element**W = Ar (x) / Mr x 100% Now, write down a formula with respect to the condition задачиW (H) = 2 Ar (H) / Mr (H2O) x 100 %Make вычисленияW (H) = 2 / 18 x 100 % = 11,1 %4

Example No. 2. Determine the mass

*fraction*of oxygen in the copper sulfate (CuSO4).Look at the table of D. I. Mendeleev of the relative atomic mass of kisloroda (O) = 16. As in formula 4 oxygen atoms, therefore 4 Ar (O) = 4 x 16 = 64Вычислите the relative molecular mass of copper sulphate (CuSO4), which consists of 1 Ar (Cu), 1 Ar (S) and 4 Ar (O).Mr (CuSO4) = Ar (Cu) + Ar (S) + 4 Ar (O).Ar (Cu) = 64, Ar (S) = 324 Ar (O) = 4 x 16 = 64, sledovatelno (CuSO4) = 64 + 32 + 64 = 1605

Write down a General formula for determining the mass fraction

**of the element**W = Ar (x) / Mr x 100% Now, write down a formula with respect to the condition задачиW (A) = 4 Ar (O) / Mr (CuSO4) x 100 %Make вычисленияW (On) = 64 / 160 x 100 % = 40 %