Experiment 1: Purification of Salt-Water by Distillation
Background:
Distillation consists of heating a liquid until it vaporizes, and then condensing the vapor
and collecting it in a separate container. Distillation is used to purify liquids, or to
separate mixtures of liquids that have different boiling points. There are many types of
distillation, each of which has a distinct purpose. For this experiment you will do a
simple distillation in order to obtain pure water from salt water.
Materials:
100 mL round-bottom flask, water condenser, distillation head, thermometer adapter,
vacuum adapter, thermometer, heating mantle, power supply, 50 mL graduated
cylinder, 2 beakers, 3 test tubes, small clamps for organic, blue glassware clamps,
boiling chips, salt water, silver nitrate
Safety Precautions:
Remember not to touch the glassware when it is very hot. Let it cool down before you
disassemble it.
Procedures:
1. Set the 100 mL round-bottom flask in the heating mantle and clamp it to a ringstand.
Place two boiling chips in the flask, measure out 50 mL of the salt-water solution, and
transfer it to the flask.
2. Assemble the rest of the distillation apparatus (see figure on last page), connecting
the pieces with the clips provided. Make sure the entire thermometer bulb is below the
sidearm of the distillation head. Water should go in on the lower side of the condenser
and exit on the upper side. Clamp the loose hose end over the sink so it doesn’t spray
the lab. Place a beaker below the end of the condenser to receive the condensed liquid.
3. Heat the flask with the heating mantle so that the liquid boils gently. The very first
liquid collected might be contaminated with organic material or salt from the glassware,
so you will throw out the first mL of distillate. To do this, switch to a fresh beaker after
about 1 mL has been collected. Record the temperature at this point as the beginning of
the collection phase. Throw out the liquid in the first beaker, but keep the beaker at you
work area because you will use it again.
4. Continue collecting liquid until about half of the original mixture has been distilled (it
is never safe to distill to dryness). Record the temperature as the end of the collection
phase, turn off the heating mantle. Liquid will continue to collect for a while. Switch the
beakers again, putting the original beaker in place to catch the last of the liquid – this is
just so it doesn’t end up on the counter. Remove the heating mantle. Let the apparatus
cool before taking it apart. The small clamps go back in the box on the cart. The blue
clamps for the glassware go back in their box on the cart. Dry off the thermometers and
put them back. The glassware should be rinsed with water, then placed in the dirty
glassware bin. Salt solutions can go down the drain.
5. Prepare three test tubes for chloride ion testing, one 2 mL sample (approx.) of each of
the following: deionized water from the lab, the original mixture, and the distillate.
6. Add 5 drops of silver nitrate solution to each test tube. The presence of chloride ion in
solution is indicated by formation of the white precipitate AgCl. Relative concentrations
are indicated by the amount of precipitate formed. Record your observations. Remove
any tape from your test tubes, pour the solutions into the waste beaker and rinse the
tubes in the sink before placing them in the dirty glassware bin.
Pre-Lab:
Prepare your notebook as described in the lab notebook handout. Include: name,
partner’s name, title of experiment, date, purpose, procedures (bulleted list), sketch of
glassware set-up (label all parts of your sketch), and data (make spaces to record
temperatures, make a table to record the chloride testing results). Leave spaces for
observations.
Report:
1. In your notebook, write a brief discussion of the experiment. In this section you
should summarize your results (how pure was your water compared to the others),
note any interesting observations and make any possible conclusions about the
experiment (successful vs. unsuccessful and reasons why).
2. Answer the post-lab questions.
3. Make a copy of your lab notebook pages (do not tear out the originals) and attach
your answers to the questions (or answer them in your notebook and photocopy with
the rest). Staple all pages and turn it in.
Post-Lab Questions:
1. Did the temperature change significantly during the collection phase? Explain why
or why not.
2. Why doesn’t the salt distill over with the water?
Example of Distillation Apparatus