Video Transcript
If two solutions of magnesium
chloride and sodium chloride have the same concentration, which one of the following
statements is considered correct? (A) The freezing point of the
sodium chloride solution is lower than the freezing point of the magnesium chloride
solution. (B) The boiling point of the
magnesium chloride solution is equal to the boiling point of the sodium chloride
solution. (C) The boiling point of the
magnesium chloride solution is lower than the boiling point of the sodium chloride
solution. Or (D) the boiling point of the
magnesium chloride solution is higher than the boiling point of the sodium chloride
solution.
Freezing and boiling point are two
examples of colligative properties. Colligative properties are
properties of solutions that vary based on the concentration of the solute in the
solution. When more of a solute is dissolved,
the freezing point will lower and the boiling point will rise. This is because the additional
solute particles will interfere with the intermolecular forces that hold liquids
together. And they are harder to convert into
gas, so the properties change accordingly.
Concentration is the determining
factor for determining the increase of a boiling point or the decrease of a freezing
point. What really matters is the number
of particles that are dissolved. Concentration is just a measure of
this.
Ionic compounds and other strong
electrolytes usually dissociate when they are in a solvent. This means that an ionic compound
like sodium chloride will split into two particles, a sodium one plus ion and a
chloride one minus ion, when it is dissolved. Similarly, magnesium chloride will
split into three particles, one magnesium two plus ion and two chloride one minus
ions. Since magnesium chloride will split
into more particles than the sodium chloride, it will cause a greater change in
boiling and freezing point if all other factors are kept constant.
So, if two sodium chloride and
magnesium chloride solutions have the same concentration, the answer is (D). The boiling point of the magnesium
chloride solution is higher than the boiling point of the sodium chloride
solution.
