Dmitri Mendeleev proposed the periodic law based on atomic mass. However, anomalies arose. In 1913, Henry Moseley discovered that the atomic number (number of protons) is the fundamental property. He proposed the modern periodic law: the properties of elements are periodic functions of their atomic numbers.
Explanation:
Calcium (Ca) has a valency of +2, and the phosphate ion (PO₄) has a valency of -3. To balance the charges, we need three calcium ions and two phosphate ions, giving the formula Ca₃(PO₄)₂. This is determined by criss-crossing the valencies of the constituent ions.
Explanation:
Froth flotation is used to concentrate sulfide ores. Galena (PbS) is a sulfide ore; it is wetted by oil (pine oil) and comes to the surface with froth, while gangue particles wetted by water settle down. Bauxite (Al₂O₃·2H₂O) is an oxide ore concentrated by leaching (Bayer's process). Magnetite (Fe₃O₄) is magnetic ore separated by magnetic separation. Carnallite (KCl·MgCl₂·6H₂O) is a halide ore.
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