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July 30, 2014

Homework Help: Chemistry

Posted by Felicity on Monday, September 11, 2006 at 5:52pm.

For a lab, we have to figure out how to separate a mixture of sodium chloride, sand, iron fillings, copper shot, and benzoic acid and recover all five components in their dry, solid states. Any ideas on how to accomplish this? Thanks!


Heat and condense the benzoic acid.
Use a magnet to pull out the iron filings.
Dissolve the NaCl in water, drain off the water, and evaporate it for pure NaCl
Separate the copper shot from sand with a sieve.


Copper shot can be picked out. Iron filings can be separated with a magnet. Benzoic acid is soluble in ether, NaCl in water (benzoic acid is somewhat soluble in water too so that must be considered) and sand is not soluble in ether or water. I will let you put all of this together. We shall be happy to review your work. I hope this helps.


Okay, but (sorry by the way) I forgot to put that the only materials we can use are alcohol, beakers, a hot plate, filter paper, distilled water, stirring rods, funnels, and ice. Thanks though!


I don't think I have ever seen a separation problem like this, especially with the limitations. This will give you some ideas. The benzoic acid sublimes at 100 degrees C. So the mixture heated to about 100 will produce vapors of benzoic acid. Place a watch glass with ice on the top (if you can use a watch glass--if not then use a beaker with ice in it) and the benzoic acid will condense on the bottom of the glass (either watch glass or glass beaker). You can scrape the bottom periodically with the stirring rods to collect the benzoic acid in a separate beaker. When all of the benzoic acid is removed, I would then dissolve the salt in water, pour through the filter paper/funnel set up, and evaporate the water to obtain the dry crystals of salt. That leaves copper shot, iron filings, and sand. The copper shot surely can be picked out by hand (surely you can use your hands; otherwise you could not handle the beakers and filter paper/funnel set up). That leaves sand and iron filings. The density of iron is about 7.5 g/cc, in rod form, and somewhat different depending upon how fine the filings are, but certainly the density will be greater than that of sand. The density of sand is about 2.0 to 3.0 g/cc depending upon how fine it is. After it is thorougly dry, (you may need to stir around with the stirring rods to get the big pieces broken up) shake the mixture. The two densities will separate themselves and you can "skim" off the top one. You may need some time to separate completely but I believe this will work. I would be interested in hearing of a different but better way. I hope this helps.


Wow. Thanks a lot! You're very smart!!!


There's no way.

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