unit twelve acids and bases
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Unit Twelve Acids and Bases. Strengths. What is an electrolyte? A solution that contains ions and will conduct electrical current Acids and bases ionize (molecular) or dissociate (ionic) into ions Dissociation – when ionic compounds break apart to form ions Examples: NaCl, NaOH, Na 2 SO 4 - PowerPoint PPT PresentationTRANSCRIPT
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StrengthsWhat is an electrolyte?
A solution that contains ions and will conduct electrical current
Acids and bases ionize (molecular) or dissociate (ionic) into ions
Dissociation – when ionic compounds break apart to form ions Examples: NaCl, NaOH, Na2SO4
Ionization – when molecular compounds break apart to form ions (acids) Examples: HCl, H2SO4
Dissolving – when solute molecules are surrounded by solvent molecules and go into solution
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StrengthsStrengths depend on how much
ionization/dissociation takes place
Strong acids and bases completely ionize/dissociate in solution 100% dissociated (lots of H+ and OH-) Strong electrolytes
Weak acids and bases do not completely ionize/dissociate in solution < 100% dissociated (only a few H+ and OH-) Weak electrolytes
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Strong versus weakFor strong acids and bases we use a single
arrow to indicate the forward reaction is favored
For weak acids and bases we use a double arrow to indicate the partial ionization (forward and reverse reactions take place)
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Strong Acids and BasesThere are six strong
acids
HClO4
H2SO4
HNO3
HCl
HBr
HI
There are eight strong basesLiOHNaOHKOHRbOHCsOHCa(OH)2
Sr(OH)2
Ba(OH)2
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WaterAmphoteric – water can act as an acid or a
base
Self-ionizations – water can also act as an acid and a base with itself! (Even neutral, pure, distilled water)
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KwIn pure water at 25°C, the preceding reaction occurs
only to a very small extent, resulting in equal, small concentrations of H+ and OH–.[H+] = [OH–] = 1.0 x 10-7 M
Ion product constant for water (Kw) – the product of the concentration of H+ and OH– in aqueous solutionsKw = [H+][OH–] Kw = (1.0 x 10-7 M)(1.0 x 10-7 M)Kw = 1.0 x 10-14 M
Can be used for aqueous solutions at 25°C (↑temp, ↑ movement, ↑ dissociation)
Kw will not change when the concentrations change because strengths are based on the amount of ionization.
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KwSince Kw is constant, and Kw = [H+] [OH‾], it
follows that: If [H+] increases, then [OH‾] decreases, andIf [H+] decreases, then [OH‾] increases.
In a neutral solution: [H+] = [OH-]In an acidic solution: [H+] > [OH-]In a basic solution: [H+] < [OH-]
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pH and pOH ScaleThe pH scale relates to the strengths
pH scale measures the hydrogen ion concentration and the pOH measures the hydroxide ion concentration
Logarithmic scale – a change in 1 pH unit corresponds to a tenfold change in [H+] (lime (pH=2) versus plum(pH=3))
pH < 7 : acidic solutionpH = 7 : neutralpH > 7 : basic solution
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pOH 13 12 11 10 9 8 7 6 5 4 3 2 1
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CalculationsKw = [H+] [OH‾]
pH = -log[H+]
pOH = -log[OH‾]
14 = pH + pOH
[H+] = 10-pH
[OH‾] = 10-pOH
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Practice ProblemsWhat are the [H+] and [OH‾] concentrations in
a 0.01 M HCl solution?
What are the [H+] and [OH‾] concentrations in a 0.0001 M NaOH solution?
What are the [H+] and [OH‾] concentrations in a 0.00001 M HNO3 solution?
What is the pH of a 0.0001 M HNO3 solution?
What is the pOH of a 0.001 M KOH solution?
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Practice ProblemsCalculate the [H+] of a solution with a pH of
8.37.
What is the concentration of OH- in a solution with a pOH of 4.80?
Calculate the pH of a solution with [OH-] = 1.3 x 10-2 M. Is the solution acidic or basic? Hint: Start with KW first to find [H+].
Calculate the OH- concentration for a solution with a pH of 3.66.
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Worksheet Two will be due Thursday