ACIDS, BASES, AND pH. 2 The solutions conduct electricity! They are called ELECTROLYTES HCl, MgCl 2,...
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Transcript of ACIDS, BASES, AND pH. 2 The solutions conduct electricity! They are called ELECTROLYTES HCl, MgCl 2,...
2
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 and Weak Strong and Weak Acids/BasesAcids/Bases
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• Weak acids are much less than 100% ionized in
water.
One of the best known is acetic acid = CH3CO2H
Strong and Weak Strong and Weak Acids/BasesAcids/Bases
Strong and Weak Strong and Weak Acids/BasesAcids/Bases
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• Strong Base: 100% dissociated in water.
NaOH(aq) ---> Na+(aq) + OH-(aq)
Strong and Weak Strong and Weak Acids/BasesAcids/Bases
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)
Strong and Weak Strong and Weak Acids/BasesAcids/Bases
Strong and Weak Strong and Weak Acids/BasesAcids/Bases
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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.
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
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-]
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++]]