Determination of pKa by absorbance and pH of buffer solutions
2018年2月3日 · We have to then plot a graph of $\mathrm{pH}$ versus $\log_{10}[A/(A_f-A)]$ and use that graph to calculate $\mathrm pK_\mathrm a$. $\text{A}_{f}$ is the absorbance of Solution 6 - we assume that the weak acid in the buffer is present only as its conjugate base - and A is the absorbance of the buffer solution. My two questions about this are:
Finding pKa from equivalence point on titration curve
2018年6月10日 · You've got a weak acid, since you're contemplating a positive pKa, which means when you're halfway to the end point you're in the buffer region and you can use the Henderson-Hasselbalch equation: pH = pKa + log [A-]/[HA] You've titrated half your initial HA, so half of it is still around and half got turned into A-, which means [A-] = [HA].
acid base - What do speciation curves really represent?
2020年4月16日 · So the ratio of the two species is equal to the ratio of equilibrium constant to proton concentration. Accordingly, the ratio changes with pH, and is equal to one when the pH is equal to the pKa. At each pH value in your graph, the acid/base reaction is at equilibrium (so the the equilibrium constant expression with the concentrations plugged ...
acid base - How can I find pKa from a titration curve? - Chemistry ...
2012年12月4日 · Viewed 2k times. 4. I am fully aware that the pKa is the pH at half the equivalence point, but are there some programs or methods I could use to accurately estimate the pKa without manually drawing lines on the graph? acid-base. analytical-chemistry.
Slope ≠ 1 in Henderson-Hasselbalch graph for determination of pKa
2021年2月28日 · Slope ≠ 1 in Henderson-Hasselbalch graph for determination of pKa. Ask Question Asked 3 years, ...
biochemistry - How can I properly calculate the isoelectric point …
2020年7月18日 · $\begingroup$ The first approach I'd say is the correct one. It's obvious that the isoelectric point will be between e1 and e2 because lysine is a dibasic aminoacid, therefore the two amino groups will have a bigger influence on the pI …
Is it correct to say that the pKa is the pH at equilibrium?
2020年4月16日 · 5. To say that "The pKa is the pH at equilibrium" isn't really true. Acid/Base reactions in aqueous solutions happen very rapidly and thus the solution reaches some equilibrium quickly. The pKa is a particular equilibrium where the protonated form of the acid and it unprotonated form are present in equal concentrations in the solution. –.
Why does pKa of a acid-base indicator equal to the pH when the ...
2015年5月2日 · The acid being used has a pKa value; So titrating acetic acid (pKa = 4.76) with NaOH, then phenolphthalein (pka = 10) is a good indicator to use since it will be colored after the neutralization reaction is complete. However bromophenol blue (pKa = 4.75) wouldn't work because it would turn blue before the neutralization reaction is complete.
ph - pKw, pKb, pKa and NEN6411 - Chemistry Stack Exchange
2021年1月27日 · Then for their conjugate acids, pKa = pKw −pKb p K a = p K w − p K b. For solutions of strong bases, pOH ≈ − log[OHX−] p O H ≈ − log [O H X −], pH =pKw −pOH p H = p K w − p O H. The graph you mention is for strong electrolytes, so pKa p K a is not applicable.
How to find pKa given absorbances and pH [closed]
2015年4月7日 · Using the Lambert-Beer Law, we can derive that. E1 E2 = ϵ ⋅c1 ⋅ d ϵ ⋅c2 ⋅ d = c1 c2 E 1 E 2 = ϵ ⋅ c 1 ⋅ d ϵ ⋅ c 2 ⋅ d = c 1 c 2. The ratio of absorbances is linear proportional to the ratio of concentrations. For a pH of 4.623, it seems fair to assume that an acetate puffer is used here. Taking this into account, you could ...