Atoms and atomic theory

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Tai lieu sinh vien AV1-2017
English-for-Chemistry-1-After-lesson-1

…(3)… . At lower temperatures, the solution becomes saturated in the desired compound. The excess compound crystallizes from solution. …(4)…

7.2 Reading:
Generally, a solvent has a limited ability to dissolve a solute. …(1)…. A solution with less
than this maximum amount is an unsaturated solution. Under certain conditions a solution
can be prepared that contains more solute than a normal saturated solution; …(2)….
Solubility refers to the concentration of solute in a saturated solution and depends on
temperature.
Compounds synthesized in chemical reactions are generally impure, but the fact that the
solubilities of most solids increase with increased temperature provides the basis for one
simple method of purification. Usually, the impure solid consists of a high proportion of the
desired compound and lesser proportions of the impurities. Suppose that both the compound
and its impurities are soluble in a particular solvent and that we prepare a concentrated
solution at a high temperature.
…(3)…
. At lower temperatures, the solution becomes
saturated in the desired compound. The excess compound crystallizes from solution.
…(4)… because the temperature is still too high
for these to crystallize. This method of purifying a
solid is called fractional crystallization, or
recrystallization.
A common method of separating the volatile
components of a solution from one another is
called fractional distillation. Boiling solutions in
equilibrium with vapor can be spread out over a
long column, called a fractionating column, in
which the equilibrium temperatures range from
…(5)…. The most volatile component in the
solution emerges from the top of the column as a

English in chemistry 1 – 2017
TS. Nguyễn Tuyết Phương – TS. Trần Thu Phương

22
vapor that is condensed to a liquid and removed. The least volatile component concentrates
in the pot at the bottom of the column. Fractional distillation of a solution of many volatile
components, such as petroleum, can be carried out in such a way that …(6)…, one by one.

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