acid base notes (h)
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Unit 11
Acids and Bases
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Name the following Acids H2CrO4
HF H3PO4
HClO4
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Acid vs Base All aqueous solutions contain H+
and OH- ions. Relative amounts determine
whether the solution is acid, base, or neutral Acid soln – more H+ (Hydronium ion) Basic soln- more OH-
Neutral- equal amounts of each
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Basic Acidic Neutral
H+
H+
H+OH-
OH-
OH-
Solution Solution Solution
Which solution is Acidic? Basic? Neutral???
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Arrhenius Model Acid is a substance that contains
hydrogen and ionizes to produce hydrogen ions in aqueous solns
Base is a substance that contains a hydroxide group and dissociates to produce a hydroxide ion in aqueous solns
Exception-NH3
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Acids and Bases
Produce H+ ions in water
Have a sour taste Break down metals Formula starts with
H Poisonous and
corrosive to skin pH less than 7
Produce OH- ions in water
Have a bitter taste and a slippery feel
Break down fats and oils
Formula ends with OH
Poisonous and corrosive to skin
pH greater than 7
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Brønsted-Lowry Model Acid- hydrogen ion donor Base- hydrogen ion acceptor
HX (aq) + H20 (l) H30+ (aq) + X- (aq)Base Conjugate AcidAcid Conjugate Base
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Conjugates Conjugate Acid
Species produced when a base accepts a hydrogen ion from an acid
Conjugate Base Species that results when an acid donates a
hydrogen ion to a base Conjugate acid- base pair
Consists of 2 substances related to each other by donating and accepting of a single H+
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Conjugates HF + H2O H3O+ + F- (H3O+ Conjugate acid)
(F- Conjugate base)
NH3 + H20 NH4+
+ OH- (NH4+ Conjugate acid)
(OH- Conjugate base) Amphoteric- substances that can act as both
acids and bases Monoprotic- HCl, HF Polyprotic- H2SO4, H3PO4
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Warm up H3PO4 + H2O H3O+ + H2PO4
-
HClO4 + H2O -ClO4 + H3O+
H2CrO4 + NH3 +NH4 + HCrO4-
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Acid Strength Strong acids – ionize completely Weak acids- do not ionize
completely
Ka =
HCN + H2O H3O+ + CN-
Ka =
][.]..][.[
AcidBCAC
][]][[ 3
HCNCNOH
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Practice Problems Write an ionization equation and
acid ionization constant expression for Nitrous Acid.
HNO2
HNO2 + H2O H3O+ + NO2-
Ka = ][
]][[2
23
HNONOOH
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One More Practice Problem Write an ionization equation and
acid ionization constant expression for Chlorous Acid.
HClO2
HClO2 + H2O H3O+ + ClO2-
Ka = ][]][[
2
23
HClOClOOH
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Base Strength Strong Bases- completely
dissociate into metal ions and hydroxide ions
Weak bases- partially dissociateBase ionization constant
Kb = ][.]..][.[
BaseBCAC
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Write ionization equations and base ionization constant expressions for the carbonate ion.
CO32-
CO32- + H2O HCO3
- + OH-
Kb =
Practice Problems
][
]][[2
3
3
CO
OHHCO
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One More Practice Problem Write ionization equations and base
ionization constant expressions for the hydrogen sulfite ion.
HSO3-
HSO3- + H2O H2SO3 + OH-
Kb = ][
]][[
3
32
HSO
OHSOH
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Warm up Write a Disassociation equation to
describe the following reactions. CO3
2- + H2O HCO3- + OH-
HClO2 + H2O H3O+ + ClO2-
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pH Measure of H+ ions in soln pH = -log[H+] Acidic solutions have a pH below 7 Basic solutions have a pH above 7 pH 7 is neutral Change of 1 pH unit represents a
tenfold change. (exponential)
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pOH Measures concentration of OH- ion
pOH = - log [OH-]
pH + pOH = 14.00
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Practice Problems Calculate the pH and pOH of
aqueous solutions having the following ion concentrations.
[OH-] = 6.5 x 10-6
pOH = -log[OH-] pH = 14.00 – pOHpOH = -log[6.5 x 10-6] pH = 14.00 –
5.19pOH = -[log 6.5 + log 10-6] pH = 8.81pOH = -[0.81 + (-6)]pOH = 5.19
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One more, one more time! Calculate the pH and pOH of aqueous
solutions having the following ion concentrations.
[H+] = 3.6 x 10-9
pH = -log[H+] pOH=14.00 – pHpH = -log[3.6 x 10-9] pOH=14.00-8.44pH = -[log 3.6 + log 10-9] pOH=5.56pH = -[0.56 + (-9)]pH = 8.44
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What is the pH of the following concentrations?
1.0 E -9 2.4 E -3 6.7 E -7 4.4 E -5
Classify each as Acid or Base
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Buffers A buffer is a mixture of a weak acid
and its conjugate base OR, a weak base and its conjugate acid.
This mixture resists changes in pH. The amount of acid or base a
buffer can absorb without significant change in pH is called the buffer capacity.
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Neutralization Reactions
When an acid is added to a base, the end products are always salt and water. (neutral)
A salt is defined as the neutral end product of an acid/base reaction.
ACID + BASE SALT + WATER H2S + Ca(OH)2 CaS + H2O What is wrong with this equation???
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Balance the final equation!
H2S + Ca(OH)2 CaS + H2O
1 Ca 11 S 14 H 22 O 1
H2S + Ca(OH)2 CaS + 2 H2O
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Neutralization Reactions
Try another example:Acid + Base Salt + Water
H2SO4 + NaOH Na2SO4 + H2O1 Na 21 SO4 13 H 21 O 1
H2SO4 + 2 NaOH Na2SO4 + 2 H2O
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Take it one step further…
Sulfurous acid and sodium hydroxide yields sodium sulfite and water.
H2SO3 + NaOH Na2SO3 + H2O
1 Na 21 SO3 1
3 H 21 O 1
H2SO3 + 2NaOH Na2SO3 + 2H2O
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One Last Step
Hydrosulfuric acid and calcium hydroxide yields what???
H2S + Ca(OH)2
1) One product will always be water. H2S + Ca(OH)2 H2O +
2) The other product will be the + ion of the base bonded with the – ion of the acid.
H2S + Ca(OH)2 2H2O + CaS
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pH Indicators A chemical substance that changes color in
the presence of an acid and/or a base.1) pH paper – Dip the paper, match color to
scale on vial to determine numeric pH.pH<7 = acid, pH>7 = base, pH = 7 neutral
2) Litmus – Dip one red and one blue paper.Red stays red, blue turns red AcidBlue stays blue, red turns blue BaseRed stays red, blue stays blue Neutral
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pH Indicators
3) Bromthymol Blue – Add a few drops of bromthymol blue to the substance.
If the blue color turns to yellow AcidIf the blue color stays blue Base
4) Phenolphthalein – Add a few drops of phenolphthalein to the substance.
If the clear liquid turns to pink BaseIf the clear liquid remains clear Acid
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Concentration
Strength of an acid or base is determined by the amount of ionization. Concentration is determined by the amount of water added to the substance.
Molarity (M)
The number of moles of solute dissolved in each liter of solution.
Molarity = moles of solute
liters of solution
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Example Problem #1
If 1.00 liter of sugar water contains exactly 1.00 mole of sugar, what is its molarity?Molarity = 1.00 mol
1.00 LMolarity = 1.00 M
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Example Problem #2
If 1.00 liter of sugar water contains exactly 2.00 mole of sugar, what is its molarity?Molarity = 2.00 mol
1.00 LMolarity = 2.00 M or 2.00 mol/L
(Twice as concentrated…)
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Example Problem #3
What is the molarity when 0.75 mol is dissolved in 2.50 L of solution?
Molarity = 0.75 mol = 0.30 mol/L or 0.30M
2.50 L
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In Lab, grams are typically used in place of moles.
If you wanted to make 2.00L of a 6M HCl solution, how much HCl would you need?
First, calculate the molar mass of the acid.H 1 x 1.00795 = 1.00795Cl 1 x 35.453 = 35.453
36.46095 = 36.461
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If you wanted to make 2.00L of a 6M HCl solution, how much HCl would you need?
First, calculate the molar mass of the acid.
HCl contains 36.461 g/mol
It would take 36.461 g of HCl to make 1 liter of a 1M HCl solution. How many grams would it take to make 2L of a 1M solution?
2 x 36.461g = 72.922g
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If you wanted to make 2.00L of a 6M HCl solution, how much HCl would you need?
It takes 72.922g of HCl to make 2 liters of a 1M solution. How much would it take to make 2 liters of a 6M solution?
6 x 72.922g = 437.532 g
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Try One More Suppose you wanted to make 2 liters of
a 0.5 M solution of HCl. How much HCl would you need?
Each mole of HCl is equal to 36.461g For a 0.5 M solution, you would need
half that much. 36.461 x 0.5 = 18.2305g.
However, you want to make 2 liters, so double that amount. 18.2305 x 2 = 36.461g.