3. Stacy reads that a 50 : 50 mixture of methanol and water is not only best for keeping a car’s radiator from freezing, but it will also take a higher temperature to make the car’s radiator boil

Question

-over. Design an experiment to test this finding. You have a hot plate, water, methanol, graduated cylinders to measure volume, several glass beakers, and a thermometer at your disposal. Be sure to state your hypothesis, procedure, and any controls in your experiment. What are the dependent and independent variables? Explain the possible results if your hypothesis is supported.

(Note: Car antifreeze is a mixture of water and another substance, commonly methanol, ethylene glycol, or another low freezing-point liquid.)

Answer 1

Hypothesis: A 50:50 mixture of methanol and water will boil at a higher temperature than water alone.

Dependent variable: boiling point

Independent variable: % methanol

Procedure:

1. Mix 100 mls methanol with 100 mls water to produce 200 mls 50:50 methanol water solution
2. Prepare another beaker with 200 mls water only. This is the control.
3. Place beaker with water only on the hot plate and heat to boiling. Record boiling point temperature.
4. Repeat with the beaker containing 50:50 mixture. Record boiling point temperature.

Results: If the hypothesis is supported, the mixture will boil at a higher temperature than the water alone. This is because of the colligative property exhibited by adding one substance to another. The boiling point will be elevated and the freezing point will be lowered. The degree to which this occurs will vary with the amount of the added substance. Thus, a 75:25 methanol:water mixture will boil at a high temperature than a 50:50 mixture. Conversely, a 25:75 methanol:water will still boil at a higher temperature than pure water, but at a lower temperature than the 50:50 or the 75:25 mixture.