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化学の教科書です。
1.6 Separating a solid which sublimes from a solid which does not sublime
E.g. separating ammonium chloride (which sublimes) from sodium chloride (which does not sublime)
A substance is said to sublime if, on cooling, its vapour changes directly from gas to solid without going through an intermediate liquid state.Usually a substance which sublimes also changes from solid to vapour without melting to a liquid.
If a mixture of ammonium chloride and sodium chloride is heated, the ammonium chloride turns directly to a vapour but the sodium chloride remains unchanged. When the vapour is cooled, solid ammonium chloride collects free from sodium chloride.
1.7 Recognizing a pure substance
A pure substance has a definite melting point. The presence of an impurity lowers the melting point but also causes the substance to melt over a range of temperature. Calcium chloride is used to lower the melting point of sodium chloride in the extraction of sodium.
The boiling point of a substance depends on pressure. At atmospheric pressure, the boiling point of a pure substance takes place at a particular temperature called the boiling point. The presence of dissolved impurities increases the boiling point slightly.
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