Hepes

Why does the equivalence point in titration 2 occur at a pH greater than 7?

The equivalence point in the titration of NaOH with CH3COOH occurred at a pH of 8.25, a pH greater than 7. A weak acid, like ethanoic acid, has a greater pH value than any strong acid. As indicated on the graph 1, the second titration started at a higher pH of about 3.7 compared to the first titration where it started at about 1.9. This difference indicates that the equivalence point and the pH at that equivalence would start on a greater pH value too if compared to the first strong acid/base titration. The equation for the reaction of ethanoic acid that is a weak acid with sodium hydroxide, a strong base would be (1st equation):

CH3COOH (aq)+ NaOH (aq) CH3COONa(aq) +H2O (l)

CH3COOH + H2O CH3COO- + H3O+

The second equation shows that all of the weak acid was converted to its conjugate weak base (CH3COO-) after reacting with the strongly basic sodium hydroxide, giving a slightly alkaline solution. At that point, which is called the equivalence point, all ethanoic acid was neutralized until no more CH3COOH was present in the solution. All protons were removed, and a slightly basic solution of pure sodium ethanoate was formed.

Why HEPES is such a useful buffer in biological systems?

The Displayed Formula of ‘’HEPES’’ Buffer explains at a high extent its effective use as a biological buffer. 4It is as a zwitterionic molecule including both a positive and a negative charge on its molecule. Like amino acids, the zwitterionic properties that <Hepes> has, explains its high solubility properties which highlight the involvement of <Hepes> in biological systems. As a result to its zwitterionic character buffers provide a balance to the solution and when acids are added they remove them from solution by accepting them.

5 Mammalian cytosolic fluid and most biological reactions have a pH range of 6.9 to 7.4. Thus, the best buffer solution to...