June 24, 2019, 10:18:42 AM
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Topic: how to prepare an acetic acid-sodium acetate buffer of the same pH and I=0.1?  (Read 456 times)

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Offline AussieKenDoll

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how to prepare an acetic acid-sodium acetate buffer of pH=5 but whose ionic strength is 0.1 from 0.1M acetic acid-sodium acetate buffer of pH=5?

Offline Borek

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You have to show you attempts at solving the problem to receive help, this is a forum policy.

http://www.chembuddy.com/?left=buffers&right=toc
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline Babcock_Hall

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What do you know about ionic strength and pKa values?

Offline AussieKenDoll

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On acetic acid-sodium acetate, there are CH3COO-,CH3+, Na+,H+ ions

0.1=1/2 [(C(+1)^2+C(-1)^2+C(+1)^2+C(-1)^2 )]
0.1=2C
C=0.05 mol dm^(-3)
CV=K
0.1mol dm^(-3)×V1=0.05 mol dm^(-3)×V2
V2/V1 =2
Make 0.05M Acetic acid/Sodium acetate buffer by taking a specific volume of the buffer and diluting buffer 2 times to achieve 0.05M.
Is this correct way of preparing an acetic acid-sodium acetate buffer of the same pH and I=0.1?
« Last Edit: March 15, 2019, 03:47:48 PM by AussieKenDoll »

Offline AWK

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For electrolyte of type 1:1 (sodium acetate) good approximation for I is c(sodium acetate). The acetic acid in this solution dissociates much less than 1 %.
What does mean CH3 ?
AWK

Offline Babcock_Hall

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There is no such thing as a CH33 ion in an acetate buffer.

Offline AussieKenDoll

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OMG sorry there is no CH3 lol
only CH3COO-, Na+,H+ ions exists

Offline AussieKenDoll

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0.1=1/2 [(C(+1)^2+C(-1)^2+C(+1)^2]
0.1=3C
C=0.034 mol dm^(-3)
CV=K
0.1mol dm^(-3)×V1=0.034 mol dm^(-3)×V2
V2/V1 =2.94
Make 0.05M Acetic acid/Sodium acetate buffer by taking a specific volume of the buffer and diluting buffer 2.94 times to achieve 0.034M.
Is this correct way of preparing an acetic acid-sodium acetate buffer of the same pH and I=0.1?

Offline AWK

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how to prepare an acetic acid-sodium acetate buffer of pH=5 but whose ionic strength is 0.1 from 0.1M acetic acid-sodium acetate buffer of pH=5?
There is something wrong with this statement. Buffer with I=0.1 will contain ~0.1 M sodium acetate.
0.1M acetic acid-sodium acetate buffer of pH=5 shows ionic strength ~0.06 to 0.07. To change its ionic strength to 0.1 not changing pH you should add both sodium acetate and acetic and calculations will be quite difficult.
AWK

Offline Babcock_Hall

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Sometimes an electrolyte is added to increase the ionic strength.  Sodium chloride would be one possibility.

Offline AWK

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Sometimes an electrolyte is added to increase the ionic strength.  Sodium chloride would be one possibility.
0
But then pH will change slightly (~0.02 ?)
AWK

Offline Babcock_Hall

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AWK,

Are you referring to the change in pKa due to change in ionic strength?  If so, then I agree that pH will change.

Offline AussieKenDoll

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Can someone please show me how do calculate it? I never done it! At least give me a link to how to solve this problem!

Offline AWK

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In the second post of this thread Borek gave you link to his lecture on buffers.
Read this chapter carefully.
AWK

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