The mass fraction of an element in substance is one of subjects which enters a chemistry course. Skills and abilities by determination of this parameter can be useful at an examination during control and independent works and also on the Unified State Examination in chemistry.
It is required to you
- - Periodic Table of D.I. Mendeleyev
Instruction
1. For this purpose that to calculate a mass fraction, it is necessary previously find the relative atomic mass (Ar) of a required element and also relative molecular mass (Mr) of substance. Further apply a formula by which the mass fraction of an element (W)W = x 100% is determined by Ar (x)/Mr, in kotoroyw - a mass fraction of an element (it is measured in shares or %); Ar (x) is the relative atomic mass of an element; Mr is the relative molecular mass of substance. For determination of relative atomic and molecular mass use the Periodic Table of D.I. Mendeleyev. At calculations surely consider number of atoms of each element.
2. Example No. 1. Define a mass fraction of hydrogen in water. Find according to D.I. Mendeleyev's table relative atomic mass vodorodaar (H) = 1. As in a formula 2 atoms of hydrogen, therefore, 2Ar (H) = 1 x 2 = 2vychislite 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, sledovatelnomr (H2O) = 1 x 2 + 16 = 18
3. Write down the general formula of definition of a mass fraction of element W = Ar (x)/Mr x 100%teper write down a formula, in relation to a condition zadachiw (H) = 2 Ar (H)/Mr (H2O) x 100%sdelayta vychisleniyaw (H) = 2 / 18 x 100% = 11.1%
4. Example No. 2. Define a mass fraction of oxygen in sulfate of copper (CuSO4). Find according to D.I. Mendeleyev's table relative atomic mass kislorodaar (O) = 16. As in a formula 4 atoms of oxygen, therefore, 4 Ar (O) = 4 x 16 = 64vychislite the relative molecular mass of sulfate of copper (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, sledovatelnomr (CuSO4) = 64 + 32 + 64 = 160
5. Write down the general formula of definition of a mass fraction of element W = Ar (x)/Mr x 100%teper write down a formula, in relation to a condition zadachiw (O) = 4 Ar (O)/Mr (CuSO4) x 100%sdelayta vychisleniyaw (O) = 64 / 160 x 100% = 40%