Buffers containing the weak base trishydroxymethylaminomethane, abbreviated Tris

Question

Buffers containing the weak base trishydroxymethylaminomethane, abbreviated Tris, are often used in biological experiments. Tris has the formula (HOCH2)3CNH2 and has a pKb of 5.91. A Tris buffer of pH 7.49 is prepared using 250.0 mL of a 0.10 M solution of Tris.. Use this information to answer the following questions.

25. To prepare the Tris buffer, what acid would be used? A) (HOCH2)3CNHCl B) (HOCH2)3CNH2Cl C) (HOCH2)3CNH3Cl D) (HOCH2)3CNH4Cl

26. What is the value of pKa of the acid? Exam 3 Version 02 Page 6 A) 2.96 B) 8.09 C) 11.82 D) 1.09

27. What must be the concentration of the acid? A) 0.40 M B) 0.10 M C) 0.25 M D) 0.025 M

28. The acid is a solid. What approximate mass of acid must be used? A) 250 g B) 16 g C) 4.0 g D) 0.10 g

With an explanation for each of the answers

Explanation / Answer

25. C) (HOCH2)3CNH3Cl tris in presence of acid amine group is protonated and turns acid from base showing buffer

26. B) 8.09 is pka value

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