Chapter21.3LearningGoals
•  Differen7atebetweenacidsandbases.
•  DefinepH.
•  Explainthesignificanceofacids,bases,andpHto
livingorganismsandtheenvironment.
21.3Whatareacids?
•  Anacidisacompoundthatdissolvesinwatertomake
apar7cularkindofsolu7on.
•  Chemically,anacidisanysubstancethatproduces
hydroniumions(H3O+)whendissolvedinwater.
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21.3Whatareacids?
Someproper7esofacidsare:
1.  Acidscreatethesourtasteinfood,
likelemons.
2.  Acidsreactwithmetalstoproduce
hydrogen(H2)gas.
3.  Acidschangethecolorofblue
litmuspapertored.
4.  Acidscanbeverycorrosive,
destroyingmetalsandburningskin
throughchemicalac7on.
21.3Bases
•  Abaseisanysubstancethatdissolvesinwater
andproduceshydroxideions(OH-).
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21.3Whatarebases?
Someproper7esofbasesare:
1.  BasescreateabiSertaste.
2.  Baseshaveaslipperyfeel,likesoap.
3.  Baseschangethecolorofredlitmus
papertoblue.
4.  Basescanbeverycorrosive,destroying
metalsandburningskinthrough
chemicalac7on.
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21.3Acidsandbases
•  Oneofthemostimportantproper7esofwaterisits
abilitytoactasbothaweakacidorasaweakbase.
•  Inthepresenceofanacid,wateractsasabase.
•  Inthepresenceofabase,wateractsasanacid.
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21.3ThepHscale
•  ThepHscalerangesfrom0to14.
–  AcidshaveapHlessthan7.
–  AbasehasapHgreaterthan7.
–  PurewaterhasapHequalto7.
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21.3ThepHscale
•  RedandbluelitmuspaperarepHindicators
thattestforacidsorbases.
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21.3pHintheenvironment
•  ThepHofsoildirectlyaffectstheavailability
ofnutrientsforplants.
Blueberries
grow best in
what pH soil?
21.3pHintheenvironment
•  ThepHofwaterdirectlyaffectsaqua7clife.
How are frogs
and amphibians
sensitive to pH
changes?
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21.3Acidsandbasesinyourbody
•  Manyreac7ons,suchastheonesthatoccurin
yourbody,workbestatspecificpHvalues.
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21.3pHandblood
•  ThepHofyourbloodis
normallywithintherange
of7.3–7.5.
•  Holdingyourbreathcauses
bloodpHtodrop.
•  HighbloodpHcanbe
causedbyhyperven7la7ng.
21.3Neutraliza7onreac7ons
•  Whenacidandbasesolu7onsaremixedinthe
rightpropor7ons,theposi7veionsfromthe
basecombinewiththenega7veionsfromthe
acid.
•  Anewioniccompoundformsandwaterisone
oftheproducts.
•  Thisisaneutraliza7onreac7on.
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