Tris (hydroxymethyl) aminomethane, commonly known as Tris, is a weak base that i

Question

Tris (hydroxymethyl) aminomethane, commonly known as Tris, is a weak base that is often used as a buffer in biochemistry. Tris-H+ + H2O ?Tris+ H_3 O^+ pK_a=8.1,MW=121.14 g/mol i) For each of the following, calculate the concentration of Tris, Tris-H+ and the pH of the solution in each of the following solutions. 12.1 g of Tris is added to water of total volume of 1 L. 4 mL of 10 M HCl added to solution in a). 1 mL of 10 M HCl added to solution in b) 1.7 mL of 10 M HCl added to solution in c) 7 mL of 10 M HCl added to solution in d) ii) For the series of HCl added condition, draw a titration curve of pH with respect to the molar equivalents of HCl added.

Explanation / Answer

two type of solutions are there.... 1). a.pH =pKa ( = log(Ka) = 14 - log(Kb) ). b.pH = pKa + log( [A-] / [HA] ), so 6.61 = 8.076 + log( [Tris] / [Tris.H+] ), and 8.79 = 8.076 + log( [Tris] / [Tris.H+] ) c.V = 2 L [Tris] = nTris / V [Tris.H+] = nTris.H+ / V pH = pKa + log( [Tris] / [Tris.H+] ) = 8.076 + log( (nTris / V) / (nTris.HCl / V) ) = 8.076 ... 2). a) Buffer capacity is greatest at pH =pKa ( = log(Ka) = 14 - log(Kb) ). b) You're close enough to the pKa to use Henderson-Hasselbalch: pH = pKa + log( [A-] / [HA] ), so 6.61 = 8.076 + log( [Tris] / [Tris.H+] ), and 8.79 = 8.076 + log( [Tris] / [Tris.H+] ) c) Calculate n = m / MW of Tris and Tris.HCl (ak...

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