Chapter 8 Laboratory: Colligative Properties of Solutions 155RQEWEvI UESTIOnS
q 1 : Did all of the solutions that you tested freeze? If not, propose and quantify an explanation for this observation.
q: 2 In the early days of automobiles, methanol was used universally as antifreeze. In 1937, antifreeze solutions based on ethylene
glycol were introduced, and quickly gained almost 100% market share, despite the fact that they cost much more than methanol.
Propose an explanation for this rapid adoption of ethylene glycol antifreeze solutions. (Hint: look up the physical properties of
methanol and ethylene glycol.)
q: 3 The Kfp for H 2 O is 1.858°C/molal. Applying this value and the van’t Hoff factors for sodium chloride (2) and sucrose (1) to the
freezing point depression values that you recorded in Table 8-2, calculate the formula weights of sodium chloride and sucrose. Record
these calculated values in Table 8-2.
q: 4 What effect on freezing point would you expect if you dissolved sufficient ethanol in water to produce a 1 molal solution?
oALIpToN ACTIvITIES
If you have time and the required materials, consider performing these optional activities:- Repeat the experiment, using solutions of ethanol or isopropanol in water. (Try solutions of 1 mL alcohol in
9 mL water, 2 mL alcohol in 8 mL water, and 3 mL alcohol in 7 mL water.) Assume a van’t Hoff factor for either
alcohol of 1, and use the freezing point depression values that you observe to calculate the formula weight of
the alcohol. (Note that ethanol is typically available as a 70% to 95% aqueous solution and isopropanol as a
70% to 91% aqueous solution, and take that into account when you make your calculations.) - Repeat the experiment, using an unknown solute provided by a parent, teacher, or lab partner. (In order to
maximize the freezing point depression, the unknown solute should be of as low a formula weight as possible,
and as high a solubility as possible. Solutions of low molality are difficult to test with a standard thermometer,
because the accordingly small value for freezing point depression is subsumed by measurement error. )
Record the value for freezing point depression, and calculate the formula weight of the solute assuming a van’t
Hoff factor of 1.