Turn on thread page Beta
    • Thread Starter
    Offline

    1
    ReputationRep:
    A scientist wished to prepare a pH 4.94 buffer solution using solutions of 0.1M acetic acid and 0.1M sodium acetate. How much sodium acetate solution should she add to 200mL 0.1M acetic acid to make the buffer solution?. The pKa of acetic acid = 4.76.

    Could some one guide me through this please? Thank you
    Offline

    0
    ReputationRep:
    Just wondering did the question specifically say 0.1M of sodium acetate? If it did then idk but if it didn't this makes the question more like the ones I've done in chem class
    • Community Assistant
    • Study Helper
    Offline

    17
    ReputationRep:
    Community Assistant
    Study Helper
    (Original post by j582)
    A scientist wished to prepare a pH 4.94 buffer solution using solutions of 0.1M acetic acid and 0.1M sodium acetate. How much sodium acetate solution should she add to 200mL 0.1M acetic acid to make the buffer solution?. The pKa of acetic acid = 4.76.

    Could some one guide me through this please? Thank you
    The first thing you need to calculate is the target concentration ratio of acid and salt.

    You do this using the acid dissociation equation and the pH

    pH 4.94 corresponds to [H+] = 1.148 x 10-5

    ka = [H+][A-]/[HA]

    1.738 x 10-5 = 1.148 x 10-5[A-]/[HA]

    Hence the ratio of salt to acid must be [A-]/[HA] = 1.514

    You now that the volume of acertic acid is 200ml and the molarity = 0.1 so the total moles of acid = 0.2 x 0.1 = 0.02

    As both the acid and salt are in the same final volume you can now deal directly in moles.

    To get the moles of salt use the relationship [A-]/[HA] = 1.514

    Hence [A-] = 1.514 x 0.02 = 0.03028 moles of salt required.

    You are told that the molarity of the salt = 0.1, therefore you need to use:

    moles = molarity x volume

    volume needed = 0.03028/0.1 = 0.3028

    303 ml (3 sig figs)
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: March 27, 2016

1,154

students online now

800,000+

Exam discussions

Find your exam discussion here

Poll
Should universities take a stronger line on drugs?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.