When two ormoreliquidsform atruesolution,they take up less space in
solutionthanthey wouldseparately.Two pintsequalIquart-butnot if one
is waterand the other alcohol. When one liquid dissolves in another, the
molecules of thesoluteoccupy the empty spaces between the molecules of the
solvent. Ina liquid the molecules are fairly far apart. Thusthe solutionis
denserthan eithersubstanceseparately and has less volume thanthe total
volumeofthe solute andsolventseparately.
HOW YOU CAN SEE THE EFFECT OF HEAT ON SOLUTIONS
Gather these materials: Crystallinesodiumthiosulfate(Na2S 203 ) ; 3 pyrex
jars;a teaspoon;andanalcoholburner.
Follow this procedure: Fill onejar2/3 full ofwater at roomtemperature.
Slowlyaddsodiumthiosulfatewith the teaspoonuntil you reach the point
where no more will dissolve. Stir the liquidconstantly,andkeeptrackof the
amountyouaddso you will knowjusthow muchofthe chemical dissolved at
roomtemperature.Recordthis amount.Put the samequantityofwaterin a
second jarand addthe same amountofsodiumthiosulfate. Now heatthe
solutionuntil small bubbles begin to form, but don'tallow it to boilbeyond
thatpoint.Afterheating,add moresodiumthiosulfate,stirringconstantlyand
keepingtrackof how much you add. Allow thejarto coolgradually.In the
thirdjar,putthe sameamountof waterandthe sametotalamountofsodium
thiosulfatethatyouaddedto the secondjar.Bring thisthirdsolutionto a full
boil and while it is boiling,addstill moresodiumthiosulfate.Allow thisjarto