What is the final pH of 1L of 1M solution of sodium acetate (NaOAc) after adding 0.1 moles of HCl? And what is the ratio and molecular fraction of OAc- and HOAc (acetic acid)?
Hello Fedaa, thank you for your question. The acid HCl will protonate some of the acetate ions when it is added to the NaOAc solution, forming undissociated acetic acid (The stronger acid displaces the weaker acid from its salt). The pH of this buffer solution is then approximately calculated using the Henderson-Hasselbalch equation according to: pH = pKs + lg c(Ac-)/c(HAc) = 4.75 + lg (0.90/0.10) = 5.7
For a closer look, you should note that the addition of the hydrochloric acid changes the volume of the solution and thus the concentrations (unless HCl was added as a gas). Even the amount of NaCl in your solution can have an effect on the pH, although NaCl should not have a buffering effect per se.
I wish you much success in your research.
Hello,
the assignment is not complete as the volume of HCl solution added to 1M / L sodium acetate is not given. Assume that this is a 1L of 0.1 M / L HCl solution to which 1 mol of solid sodium acetate has been added. An approximate calculation is already given by Florian Morsbach. This is an approximation, because with such a concentrated solution it is not possible to neglect the activity coefficients of the individual components. Probably a slightly more accurate estimate can be obtained by calculation in PhreeqC (PhreeqcI 3, database Minteq).
Equilibrium pH 5.472 was calculated. (Ionic strength (mol/kgw) = 8.490e-01)
More interesting than pH is the estimate of the composition of the solution (in fig.). In the solution, dissociated acetate ions still predominate over undissociated Na acetate. The proportion of undissociated acetic acid is still low.
About the pH for sodium acetate / acetic acid solutions with added hydrochloric acid; cf. my posts at:
https://www.researchgate.net/post/Can-hydrochloric-acid-be-used-to-acidify-sodium-acetate
On predicting the pH of pure sodium acetate aq. sol.; see: https://www.researchgate.net/post/Can_we_keep_the_pH_of_3M_Sodium_Acetate_around_7_instead_45-5_while_using_this_in_DNA_extraction_from_whole_blood
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