THE CHEMISTRY OF SOLUTIONS,
DIFFUSION AND OSMOSIS
When salt (NaCt) or sugar (C12H 220 u)dissolves in water, the water remains
clear andcolorless, but tastes salty or sweet. Whencoppersulfate(CuS0 4 )
dissolves in water, the water remains clear but it turns blue. A fewdropsof
ink in a glass of water have a similar effect on the water. A liquidcontaining
anothersubstancedissolved in it is asolution,regardlessofhow much of the
othersubstanceor how many different substances are dissolved in it. Asolution,
therefore,is a clear liquid mixture of two or more substances, the amounts
ofwhich may vary. Asolutionis never lumpy. The liquid in which the sub-
stances dissolve is called thesolvent,and the dissolved substances themselves are
solutes.A cupoftea then is asolution,in which the solvent ishotwater or a
mixtureofhotwater with lemon or milk. The solutes are the sugarandthe
chemicals from the tea leaves.
Wateris sometimes called the"universalsolvent"becausealmosteverything
dissolves in it, at least a little. Here are some curious factsaboutsolutions.
The higher thetemperatureof the solvent, the more easilysolutionsform,
andalso thegreateris the proportionof solute thatactually dissolves. This
is why sugar dissolvesbetterin hot teathanin iced tea.
Gases are the exception to this rule. They dissolve more easily in cold liquids
thanin hot ones. This is why soda gets"flat"when you allow it tostandun-
cappedoutsidetherefrigerator.As the liquid gets warmer, the gas(carbon
dioxide)containedin thesolutionescapes.
The smaller the particles ofthe solute, the more easily a solutionforms.
This is why finelygroundsugar is used in iced tea.
When one liquid dissolves inanother,thecombinationinsolutionoccupies
less spacethaneither liquid occupied separately. ThecombinationofI quartof
waterandI quartofalcoholmakes lessthan2 quartsinsolution.
Some of the most vital processesoflivingcreatures depend on the ability
ofsolutionsto passthrougha very thin typeofskin called amembrane.This
is the process ofosmosis.Withoutosmosis, minerals and water from the soil
wouldn'tget intoplants;oxygenwouldn'tget into our blood, andneitherwould