lab 3: buffering agents & titration curves

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22 Terms

1
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what is a buffer?
an aqueous solution composed of weak acid or base to maintain a nearly constant pH in an environment
2
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what is an example of buffer?
blood, pH range must be within 7.35-7.45; above 7.8 or below 6.8 = death
3
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how will we determine the formula weight and pKa and identity of the unknown buffing agent?
acid and base titration curves
4
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what is the main characteristic of a buffering agent?
pKa
5
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what is an acid?
a molecule that can dissociate, releasing a hydrogen ion
6
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what is a base?
a molecule that can accept a hydrogen ion
7
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what is the dissociation of a weak acid formula?
CH3COOH < - > CH3COO- + H+
8
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how is dissociation constant expressed?
Ka
9
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what is the formula for Ka for a weak acid?
Ka = (\[CH3COO-\]\[H+\])/\[CH3COOH\]
10
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what is an example of a weak acid?
acetic acid
11
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how is the Henderson-Hasselbalch equation used?
to describe the action of a buffer when a strong acid or strong base is added to a weak acid or weak base
12
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what is the Henderson-Hasselbalch equation?
pH = pKa + log10(\[A-\]/\[HA\])
13
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what are buffering agents?
molecules that prevent a system from changing too much; in this experiment
14
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what are the most common buffering agents?
HEPES and Tris
15
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when do buffers have their highest buffering capacity?
near their pKa value
16
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how can we define pKa under the circumstance \[A-\] = \[HA\]?
the pH at which the concentrations of the protonated and unprotonated forms are equal; also occurs when titratable (ionizable) group is at its best buffering capacity
17
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what is the rule with ionizable groups and pKa?
the ionization of each titratable group follows the Henderson-Hasselbalch equation
18
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what is a pH indicator?
a reagent that indicates the degree of acidity or basicity of a solution through color change often served as a visual control of pH solutions
19
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what is the equivalence point?
the point at which the pH rises (or falls) sharply with addition of base or acid; the point the moles of added strong base or acid is equal to the moles of your unknown compound
20
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how much is allowed between the pH range to still reach its capacity?
\+/- 1 pH around its pKa
21
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what is the blood buffering equation?
H2O + CO2 < - > H2CO3 < - > H+ + HCO3-
22
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what is the inflection point?
when protonated and unprotonated forms of the acid or base are equal