ACIDS, BASES, AND pH

ACIDS, BASES, AND pHACIDS, BASES, AND pH

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The solutions conduct electricity!They are called

ELECTROLYTES

HCl, MgCl2, and NaCl are strong

electrolytes. They dissociate completely (or

nearly so) into ions.

Aqueous SolutionsAqueous SolutionsHow do we know ions are present?

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Aqueous SolutionsAqueous Solutions

weak electrolyte,like Acetic acid, ionizes only

to a small extent,

CHCH33COCO22H(aq) H(aq)

CHCH33COCO22--(aq) + H(aq) + H++(aq)(aq)

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Aqueous SolutionsAqueous SolutionsSome compounds dissolve

in water but do not conduct electricity. They

are called

nonelectrolytes..

Examples include:Examples include:sugarsugar

ethanolethanolethylene glycolethylene glycol

Examples include:Examples include:sugarsugar

ethanolethanolethylene glycolethylene glycol

Acid PropertiesAcid Properties Sour taste (grape fruit)Sour taste (grape fruit) Found in many fruits Found in many fruits VinegarVinegar Will burn if not dilutedWill burn if not diluted Made up of NonmetalsMade up of Nonmetals Acid formulas usually start Acid formulas usually start

with hydrogen- ex HCl, Hwith hydrogen- ex HCl, H22SOSO44

Base PropertiesBase Properties Bitter taste Slippery feel Most household cleaners Also dangerous if not diluted Made up of a metal and

nonmetals in formulas Arrhenius bases start with metals

in their formulas and end with a OH- ex NaOH, KOH, Ba(OH)2

Arrhenius Arrhenius TheoryTheory Substances ionize in Substances ionize in

waterwaterAcids, bases, and salts Acids, bases, and salts when dissolved in water, when dissolved in water, will will conduct electricityconduct electricity..

Called ElectrolytesCalled Electrolytes

Arrhenius TheoryArrhenius Theory AcidsAcids release hydrogen release hydrogen

ions ions (H(H++)) HCl → HCl → HH++ + Cl + Cl--

BasesBases release hydroxide release hydroxide ions ions (OH(OH--))

NaOH → NaNaOH → Na++ + + OHOH--

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Strong and Weak Strong and Weak Acids/BasesAcids/Bases

• Generally divide acids and bases into STRONG or WEAK ones.

STRONG ACID: HNO3(aq) + H2O(liq) --->

H3O+(aq) + NO3-(aq)

HNO3 is about 100% dissociated in water.

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HNO3, HCl, H2SO4 and HClO4 are among the only known strong acids.


Strong Acids will completely ionize

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• Weak acids are much less than 100% ionized in

water.

One of the best known is acetic acid = CH3CO2H



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• Strong Base: 100% dissociated in water.

NaOH(aq) ---> Na+(aq) + OH-(aq)


Other common strong bases include KOH and

Ca(OH)2.

CaO (lime) + H2O -->

Ca(OH)2 (slaked lime)CaOCaO

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• Weak base: less than 100% ionized in water

One of the best known weak bases is ammonia

NH3(aq) + H2O(liq) e NH4+(aq) + OH-(aq)



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ACID-BASE THEORIESACID-BASE THEORIESACID-BASE THEORIESACID-BASE THEORIES

• The most general theory for common aqueous acids and bases

is the BRØNSTED - LOWRY theory

•ACIDS DONATE H+ IONS

•BASES ACCEPT H+ IONS

Bronsted Bronsted BaseBase: adds : adds one one hydrogen ionhydrogen ion

Bronsted Bronsted AcidAcid: removes : removes oneone hydrogen ion hydrogen ion

Reactants Products

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ACID-BASE THEORIESACID-BASE THEORIESACID-BASE THEORIESACID-BASE THEORIES

NH3 is a BASE in water — and water is itself an ACID

NH3 / NH4+ is a conjugate pair —

related by the gain or loss of H+

Every acid has a conjugate base - and vice-versa.

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Conjugate PairsConjugate Pairs

You PracticeYou PracticeNHNH33 + H + H22O → NHO → NH44

++ + OH + OH--

HNOHNO33 + NaOH → H + NaOH → H22O + NaNOO + NaNO33

NaHCONaHCO33 + HCl → NaCl + H + HCl → NaCl + H22COCO33

Amphoteric Amphoteric A substance having A substance having the ability to act as the ability to act as an acid or a basean acid or a base

or AmphoPROTICor AmphoPROTICHydrogen ion = protonHydrogen ion = proton

Water is an Water is an exampleexample

Water is amphoproticWater is amphoprotic

It can gain and It can gain and lose a H+lose a H+

Hydronium ion Hydronium ion – An ion – An ion formed when a free Hformed when a free H++

forms with water to form forms with water to form an Han H33OO++

Why is Water Neutral?Why is Water Neutral?

When one water gains, When one water gains, another loses a H+another loses a H+

[H[H33O+ ] = [OH-]O+ ] = [OH-]

The pH scale only for water

solutionsBasic = more OH-

Acidic = more H3O+

Neutral H3O+ = OH-

Relative ion Relative ion concentrationsconcentrations

ppHH is a relative measure of is a relative measure of the the hydrogen ionhydrogen ion concentrationconcentration

ppHH is a is a ratingrating; ; ranges fromranges from 0 – 14 0 – 14

0 = most0 = most,, 7 equal, 7 equal, 14 = least14 = least

Why at a pH = 7 ?Why at a pH = 7 ?

Determined by concentration [ X ] of Determined by concentration [ X ] of each ioneach ion

[H+ ]= [OH-] = 10[H+ ]= [OH-] = 10--77MM

The concentration of hydrogen ion The concentration of hydrogen ion equals the concentration of hydroxide equals the concentration of hydroxide

ion equals ten to the negative ion equals ten to the negative seventh molar concentrationseventh molar concentration

Need to remember molarity and concentrationNeed to remember molarity and concentration

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[H[H33OO++], [OH], [OH--] and pH] and pH

A common way to express acidity and basicity is with pH

pH = - log [HpH = - log [H33OO++]]

In a neutral solution, [H3O+] = [OH-] =

1.00 x 10-7 at 25 oC

pH = -log (1.00 x 10-7) = - (-7) = 7

Relative ion Relative ion concentrationsconcentrations

ppOHOH is a relative measure is a relative measure of the of the hydroxide ionhydroxide ion concentrationconcentration

ppOHOH is a is a ratingrating; ; ranges fromranges from 0 – 14 0 – 14

0 = most,0 = most, 7 equal, 7 equal, 14 = least14 = least

Any pAny pXX Scales ScalesAny pAny pXX Scales Scales

In generalIn general pX = -log XpX = -log X

pOH = - log pOH = - log [OH[OH--]]

pH = - log [HpH = - log [H++]]

Determining pOHDetermining pOH

pH + pOH = 14If know one can determine the other.

If pH = 13, what is the pOH?13 + pOH = 14

pOH = 14 – 13 = 1

ACIDS, BASES, AND pH

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