CHAPTER 8: ACID – BASE EQUILIBRIUM 4 U CHEMISTRY
P 526 – SEE KEY IDEAS
examples f acids and bases.
8.1: The Nature of Acid – Base Equilibria:
Arrhenius acids – H ions in water, bases – hydroxide ions in water -
acids – sour, turn blue litmus to red (pink), conduct electricity -
bases – bitter, soapy taste, slippery, conduct electricity, turn red litmus to blue
Bronsted – Lowry Theory:
acids – donate proton, bases accept proton
ex: HCl donates proton to water ( not reversible )
ex: water donates proton to ammonia – reversible
Amphoteric substances: ____________________________________________________________ -
Advantage of B-L definition:
1. reactions can be identified as acid-base neutralization reactions without water -
2. salts that form acidic or basic solutions when dissolved can be explained
Reversible Acid – Base Reactions
many B-L acid-base reactions are reversible
Conjugate acid – base pair – differ only by one H
ex: H2O and H3O +
A Competition for Protons
stronger c-acid succeeds in donating the most protons, has a weaker c-base -
stronger c-base succeeds in accepting the most protons, has a weaker c-acid -
the strong acid and strong base are always on the same side of the reaction arrow -
99 % ionized = strong acid, ex: HCl
SUMMARY p 531
p 532 practice # 1, 2, 3.
The Autoionization of Water
2 molecules may collide and one molecule accepts a proton from the other – see p 532 -
equilibrium of the reversible reaction – can write the constant -
Kw = [H +] [OH –1 ] = (1.0 x 10 –7 )2 = 1.0 x 10 –14 -
Kw changes at different temp ( remember concept from ch 7 ) -
so pH of pure water changes with diff temp
but pure water always neutral since # protons = # hydroxide ions
ionize more than 99 % in water ex: HCl
monoprotic acids – have only one ionizable H ex: HNO3
p 537 practice # 4, 5, 6.
ionic substances, dissociate 100 % in water, but not all are very soluble -
ex: NaOH and other gp 1 hydroxides (soluble), Mg(OH)2 and other gp 2 hydroxides (slightly soluble) -
DON’T drink NaOH ! it will react with the tissues of your mouth ant throat and destroy them!! -
but people regularly eat Mg(OH)2 - as an antacid – it doesn’t dissolve on the way to the stomach, and then only dissolves enough to react with stomach acid to neutralize it -
[OH –1]= concentration of strong base x # OH –1 groups per formula unit. Ignore OH –1 from water p 540 practice # 8, 9, 10, 11.
Hydrogen Ion Concentration: pH = – log [H +]
used to express conc that are smaller than 1 because neg exponents can sometimes be confusing -
SIG DIG’s count ONLY for the decimal numbers of a pH value -
pOH = – log[OH –1]
pKw = – log Kw = 14 at SATP
pOH + pH = 14 at SATP
indicators – weak acids or weak bases that change colour with the addition or removal of the ionizable hydrogen ex: bromthymol blue ( BTT ) that we used in an investigation -
pH meters – change of electrical conductivity is converted into pH
pH of Strong Acids and Bases:
conc of hydrogen ion = conc of the strong acid if the acid is monoprotic, H+ from water is negligible -
OMIT calculations of acids that are diprotic or higher.
[OH –1] = concentration of strong base x # OH –1 groups per formula unit. Ignore OH –1 from water
SUMMARY p 549
p 546 practice # 12, 13, 14, 15ab, 16a.
p 549 practice # 17, 18, 19.
p 549 – 550 section 8.1 practice # 1, 2, 3, 4.
8.2: Weak Acids and Weak Bases
ex: _________________________________________________________________________________ -
form equilibrium solutions between ionized and molecular forms
Weak Acids: _________________________________________________________________________
react with water to ionize the water so OH –1 ions exist in the solution -
weak bases are proton...
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