Video Transcript
The graph provided shows the
solubility curves of four different substances. Part (a) what is the solubility of
aluminum nitrate at 12 degrees Celsius? (A) 68 grams per 100 grams of
water, (B) 34 grams per 100 grams of water, (C) 32 grams per 100 grams of water (D)
23 grams per 100 grams of water, or (E) 60 grams per 100 grams of water.
Solubility is the maximum amount of
solute in grams which can dissolve in a given amount of solvent, usually 100 grams
or 100 milliliters at a certain temperature. The question asks about the
solubility of aluminum nitrate at 12 degrees Celsius. So, if we go to 12 degrees Celsius
and up to the aluminum nitrate curve and then across to the 𝑦-axis, we get a value
of about 68 grams of aluminum nitrate per 100 grams of water. This is the maximum mass of
aluminum nitrate that can dissolve in 100 grams of water at 12 degrees Celsius. So, the solubility of aluminum
nitrate at 12 degrees Celsius is 68 grams per 100 grams of water.
(b) At what temperature is the
solubility of ammonium chloride and potassium nitrate the same? (A) 23 degrees Celsius, (B) 44
degrees Celsius, (C) nine degrees Celsius, (D) 26 degrees Celsius, or (E) 57 degrees
Celsius.
The solubility of ammonium chloride
and potassium nitrate will be the same where their curves or graphs intersect, which
is at this point. They both have a solubility of
approximately 40 grams per 100 grams of water at 26 degrees Celsius, which is the
𝑥-axis value corresponding to where the two curves intersect. So, the temperature at which
ammonium chloride and potassium nitrate have the same solubility is 26 degrees
Celsius.
(c) A student wants to dissolve
exactly 40 grams of potassium chloride in 100 grams of water. To what temperature will they need
to heat the water? (A) 60 degrees Celsius, (B) 40
degrees Celsius, (C) 26 degrees Celsius, (D) 64 degrees Celsius, or (E) 80 degrees
Celsius.
We are told that the student wants
to dissolve exactly 40 grams of the solute potassium chloride in 100 grams of
water. If we go to 40 grams on the 𝑦-axis
across to the potassium chloride curve and down to the 𝑥-axis, we find a
temperature of 40 degrees Celsius. In fact, this is the temperature at
which the maximum mass of potassium chloride that can dissolve in 100 grams of water
is 40 grams.
So, the temperature to which the
student will need to heat the 100 grams of water to dissolve exactly 40 grams of
potassium chloride is 40 degrees Celsius. Now because 40 grams is the maximum
amount that can dissolve in 100 grams of water at 40 degrees Celsius, even if the
student added more than 40 grams of potassium chloride, only 40 grams would dissolve
in this mass of water at this temperature.
