the residue.Thenfill in the rest of thecolumnsonyourdatasheet. When you
reach the eighth tube, boil until only!ofan inchofliquid remains. Let it
cool slightly and taste it. Fill in the final entries for the alcohol. Now, for each
substance,compareall thedatapertainingtoappearanceand taste.
Results: Some of thesesubstancesdissolved more readily thanothers,but
they all dissolved when thetemperatureincreasedenough. Each solutionwas
clear and colorless, except thecoppersulfatesolution,which was clear and blue.
Afterthe first sevensolutionsevaporated,crystals remained in the tubes. It
was thewaterthatevaporated,not the crystals, because the water has a lower
boiling point. Some of the crystals were exactly the same as before, and some
assumed a slightly different formation. They all tasted the same as before,
except thealcoholsolution,which left no crystals of course. In this case, the
alcoholevaporated,not the water, becausealcoholhas a lower boilingpoint
thanwater. After thealcoholboiled off,therefore,thewaterno longer had an
alcoholtaste.
Evaporationis a quick and efficient meansofseparatingsolvents and solutes.
Itis used inextractingsugar from cane syrup and in purifyingsalt. The process,
when followed bycondensation,is calleddistillation,as you know, and is used
to purify water for specialpurposes.
HOW TO TELL IF A SOLUTION IS AN ELECTROLYTE
Gather these materials: Six smalljars;2 dry cells; three 6-inch lengthsof
insulatedcopperwire and one 4-inchlength;a small flashlightbulb;a kitchen
knife or penknife; dilute sulfuric acid (H2S0 4 ) ; acetic acid (CH3COOH);
sodiumchloride(NaCl);starch(C6H 100 S);magnesium sulfate(MgSOJ;and
saladoil.
Follow this procedure:Arrangethe 6jarsin a row and label each one with
the name of one of the chemicals listed above. Fill the first 5jarshalfway with
water. Add 1t teaspoonfulsofsulfuric acid to thejarlabeled"sulfuricacid,"
Itteaspoonfulsofacetic acid to thejarlabeled "aceticacid,"and so forth
until you get to thejarlabeled"saladoil."Fillthatjar,whichcontainsno water,
halfway withsaladoil.
Usingyourpenknife, remove-tinch ofinsulationfrom bothends of each
piece ofcopperwire. Connectoneofthe 6-inch lengths of wire to one of the
dry cells at theoutsideterminal. Make theconnection by winding the wire
1 t coilsaround the terminal.Connectthecentralterminal ofthe same dry
cell to theoutsideterminalof the second dry cell with the 4-inch length of wire.
Connectthe second 6-inch length of wire to thecentralterminalof the second