outof its molecules. Examplesofacids are hydrochloricacid (HCl), sulfuric
acid (H2S0 4 ) ,andcarbonicacid (H2C0^3 ) .Abase(the same as an alkalifor
allpracticalpurposes)is asubstancewith an OH radical thatcan easily be
pushed outof its molecules. Examples of bases are ammoniumhydroxide
(NH40H),calcium hydroxide(Ca(OH)2)' and potassium hydroxide (KOH).
Saltsform when an acidandbase react with oneanother.The salt is a com-
poundconsistingof thecombinationof atoms left over after the freeH'shave
detachedthemselves from the acid and the free OH'sfrom the base. The
detachedH'sandOH'sjointo become water. Examplesofsalts aresodium
chloride (NaCI), magnesium sulfate (MgS0^4 ) , and copper sulfate (CuS0^4 ).
When a salt is formed, water is also formed.
Let us take as atheoreticalexample thereactionbetween the base, calcium
hydroxide(Ca(OH)2) and the acid,carbonicacid (H2C0^3 ) .Calciumhydroxide
has two OH radicals andcarbonicacid has two H's. When youputthis acid
andbasetogether, you knowthattheH'sandOH'swilldetachthemselves
from the acid and base, respectively, and willcombineto form water. You
know alsothatthe atoms leftover-theCa, C, andO's-willcombineto form a
salt. See then if you can figureouttheequationfor thisreaction:
H2C0 3 +Ca(OH)2-+2H^20 +CaC0^3
Naturally,it is veryimportantto be able to tell if a molecule has a free H
atomor OH radicalto give up, inotherwords, if it is an acid or a base.
Chemists have foundcertainsubstances,calledindicators,which change color
when they are close to substancescontainingfree H atoms or OH radicals. In
the following experiments, you will learn how to use someoftheseindicators.HOWYOU CANTELLANACID FROMABASE
Gather thesematerials:Carbonicacid (H2C0^3 ) ;a solutionofsodiumchloride
(NaCl);a dilutesolutionofammoniumhydroxide(NH40H);a dilutesolution
ofsodiumhydroxide(NaOH);hypochlorousacid(HClO);magnesiumsulfate
(MgS0 4 ) ; boric acid (H3B0^3 ) ; acetylsalicylic acid (CH3COOC6H4COOH);
ethanol(C2HsOH); salad or mineral oil (basically (CH2)16C02H);sodiumbi-
carbonate(NaHC0 3 ) ;^11 testtubes;some testtuberacks;blueandred litmus
paper;andpaperand pencil.
Follow this procedure:Set up the test tubes in the racks and label each one
with one of the chemical names listed above.Put-tteaspoonfulof each chemical
into the correcttube. Add enough water to fill the tubes toapproximately
1/3 their height.Makea datasheet similar to the one here, and as youproceed,
fill in the spaces.