Use the following steps to determine how to make 600 mL of a 0.1M acetate buffer
ID: 487835 • Letter: U
Question
Use the following steps to determine how to make 600 mL of a 0.1M acetate buffer, pH 5.0, using 0.1M acetic acid and 0.1M sodium acetate. Using the desired pH(5.0) and pKa of acetic acid, use the Henderson-Hasselbalch equation to determine a ratio of [base]/[acid] required for this buffer. Your answer should look something like [base]/[acid] = 2.3 Given the example above, we can set [acid] = x and [base] = 2.3x. Remember that the concentration of acid and base should equal the desired molarity, which 0.1. Based on this, a second equation can be obtained given the example above, the equation would be x + 2.3x = 0.1. Use this to solve for x, which represents the concentration of acid ([acid]), and also for [base]. Use M_1V_1 = M_2V_2 to solve for the volume of 0.1M acetic acid and 0.1M sodium acetate required to create the buffer. M_1 = 0.1M of acetic acid or 0.1M sodium acetate (stock solution) V_1 = what to solve for M_2 = the value for [acid] or [base] solved in 4b V_2 = the desired buffer volume (600mL)Explanation / Answer
Answer:
a) Henderson - Hasselbalch equation to find pH of buffer is,
pH = pKa + log([Base]/[Acid]
For Acetic acid - Sodium acetate buffer,
Required pH = 5.0 unit, pKa of Acetic acid = 4.76 using these values,
5.0 = 4.76 + log([Sodium acetate]/[Acetic acid]
log([Sodium acetate]/[Acetic acid] = 5.0 - 4.76
log([Sodium acetate]/[Acetic acid] = 0.24
[Sodium acetate]/[Acetic acid] = 100.24.
[Sodium acetate]/[Acetic acid] = 1.74.
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b) We have, [Sodium acetate]/[Acetic acid] = 1.74.
Let the concentration of [Acetic acid] = 'x' M then
[Sodium acetate] = '1.74 x' M
We want to prepare 0.1 M buffer and hence we write,
Molarity of Acetic acid + Molarity of Sodium acetate = 0.1
So, x + 1.47x = 0.1
2.74 x = 0.1
x = 0.1 / 2.74
x = 0.0365.
Hence,
[Acetic acid] = x = 0.0365 M and [Sodium acetate] = 1.74x = 1.74 x 0.036 = 0.0635 M
[Acetic acid] = 0.0365 M and [Sodium acetate] = 0.0635
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c)We have to take solutions as,
[Acetic acid] = 0.0365 M and [Sodium acetate] = 0.0635.
Let us calculate volume required of the each of the component,
i) For Acid componanant.
M1 = 0.1 M (Stock), V1 = ? M2 = 0.0365 M, V2 = 600.
M1V1 = M2V2
0.1 x V1 = 0.0365 x 600
V1 = 0.0365 x 600 / 0.1
V1 = 219 mL.
Note we can have volume of base componant = 600 mL - 219 mL = 381 mL
but shown calculations for trust on method used.
ii) For Basic componant,
M1 = 0.1 M (Stock), V1 = ? M2 = 0.0635 M, V2 = 600.
M1V1 = M2V2
0.1 x V1 = 0.0635 x 600
V1 = 0.0635 x 600 / 0.1
V1 = 381 mL
Answer :
On mixing 219 mL of 0.1 M Acetic acid to 381 mL of 0.1 M Sodium acetate we get 600 mL of Acetate buffer
with pH = 5.
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