A buffer solution is preapred so that the concentrations of conjugate weak acid
ID: 812671 • Letter: A
Question
A buffer solution is preapred so that the concentrations of conjugate weak acid and conjugate weak base are the same: 0.150 mol/L. IF 0.01 moles of solid NaOH are added to this buffer solution one can say:
a.) The pH will not change at all
b.) After the reaction, the concentration of the weak acid will be greater than the concentration of the weak base
c.) After the reaction, the concentration of the weak base will be 0.16 mol/L
D.) The PH will be determined by the excess of the strong base
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Please Give a brief Explanation for both
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Which of the following solutions makes the best buffer?
a.) [HA]= 0.0010 M & [NaA] = 0.0010 M
b.) [HA] = 0.150 M & [NaA] =0.00150 M
c.) [HA] = 0.150 M & [NaA] = 0.150 M
d.) [HA] = [NaA]
e.) The buffer efficacy of all the solutions is the same
Explanation / Answer
First, let's right the overall reaction of a buffer solution when OH- is added and let's assume 1 L of solution
HA + OH- --------> A- + H2O
initital: 0.15 mol - 0.15 mol
addition 0.01
Changes: -0.01 -0.01 +0.01
Final moles: 0.14 ? 0.14
Final concentration: 0.14 M 0.16 M
For buffer solutions:
pH = pKa + log ([A-]/[HA])
Because the rate of concentrations results in (0.16/0.14) = 1.14 and log (1.14) = 0.06, we'll find that the pH variates in the second significant figure, almost nothing. We can affirm then that:
a) The pH will not change at all and
c) After the reaction, the concentration of the weak base will be 0.16 mol/L
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e) The buffer efficacy of all solutions is the same, because a buffer solution is one where the concentration of base and acid is almost the same and no significant change is made when base or acid are added.
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