Transcript 2002 AP

2002 AP
Calculate the value [H+] in
an HOBr solution that has a
pH of 4.95
Calculate [H+]
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Given the pH is 4.95
Use the exponent 10 raised the –pH
This will yield the [H+]
Write the equilibrium
constant expression for the
ionization of HOBr in an
HOBr solution with a [H+]=
1.8 x 10^(-5)
Equilibrium constant expression
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Given the chemical
equilibrium reaction and
the concentration of
[H+]
[H+] = [OBr-]: This is
true because as HOBr
dissociates the products
form in same
proportions
Exclude x because it is
negligible.
Use the Law of Mass
action Products over
Reactants raised to their
stoichiometric
coefficients.
Equilibrium constant expression
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Use the
equilibrium
constant.
The product of
the
concentration
divided by the
Ka yields the
concentration of
HOBr.
Calculate the volume of
0.115M Ba(OH)2 needed to
reach equivalence when
titrated into 65mL sample of
0.146M of HOBr
Calculate Volume Needed to
Reach Equivalent Point
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Convert the Volume of
HOBr to liters
Multiply the volume in
Liters by the Molarity of
HOBr in Solution
This will give you the
moles of the HOBr in
solution
The titrant used is
Ba(OH)2 (Strong Base) so
the concentration of OHmust be doubled therefore
you must multiply the
concentration of Ba(OH)2
to get the concentration of
OH-
Calculate Volume Needed to
Reach Equivalent Point
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Take the Moles of
HOBr (HOBr = OH) that was
calculated and
divide it by the
molarity of OH([Ba(OH)2] x 2).
This will give you
the volume in liters
necessary to added
to reach eq point
Indicate whether the pH at
equivalence point is less
than 7, 7, or greater than
seven. Explain
What will the pH at the eq point be?
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You can go through the calculations
to determine the pH specifically at
the eq point.
The basic rule of thumb is that if you
are titrating a weak acid with a
strong base then the pH at the end
point will be greater than 7.
Calculate the number of the
moles of NaOBr(s) that
would have to be added to
125mL of 0.160M HOBr to
produce a buffer solution
with a [H+] of 5.00 x 10^(-9)
Number of Moles needed to
produce certain Concentration
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The HendersonHasselbauch
equation can be
used for this
scenario (See
equation Below)
Given the [H+]
take the –
log([H+]) and
determine the pH
for the equation
Number of Moles needed to
produce certain Concentration
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You have already been given the Ka
so plug that in the equation as well
Separate the ratio of concentrations
into log(B) – log (A) (Refer to Log
Rules)
Number of Moles needed to
produce certain Concentration
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Solve for the Log
(Base) and then
eliminate the log
function by raising
the solution using
the base of 10.
This will yield your
concentration of
Base
Number of Moles needed to
produce certain Concentration
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Multiply the concentration by the
volume of solution in liters
This will yield the number of NaOBr
moles