   Chapter 2, Problem 40RE

Chapter
Section
Textbook Problem

MATHEMATICAL A catalog in the lab has a recipe for preparing 1 L of a TRIS buffer at 0.0500 M and with pH 8.0: dissolve 2.02 g of TRIS (free base, MW = 121.1 g/mol) and 5.25 g of TRIS hydrochloride (the acidic form, MW = 157.6 g/mol) in a total volume of 1 L. Verify that this recipe is correct.

Interpretation Introduction

Interpretation:

The given recipe is to be verified.

Concept information:

Buffers are the solutions that have the capability of resisting any kind of change.

On the other hand, buffer systems are the solutions that are capable of resisting any change in the pH if added with some amount of a strong base or a strong acid.

The Henderson–Hasselbalch equation states the relationship between the pKa value of an acid and the pH of a solution that contains an acid along with its conjugate base. The equation is as follows:

pH=pKa+log[A-HA]

Explanation

Given information: A catalog in the lab has a recipe for preparing 1 L of a TRIS buffer at 0.0500 M and with pH 8.0: dissolve 2.02 g of TRIS(free base, MW=121.1 g/mol) and 5.25 g of TRIS hydrochloride (the acidic form, MW=157.6 g/mol) in a total volume of 1 L.

Calculating the molar amount of the two forms as follows:

The molecular weight (MW) of TRIS =121.1 g/mol

Therefore, the number of moles of TRIS is calculated as follows:

Number of moles=2.02 g121.1 g/mol=0.0167 mole

The molecular weight (MW) of TRIS hydrochloride =157.6 g/mol

Therefore, the number of moles of TRIS hydrochloride is calculated as follows:

Number of moles=5.25 g157.6 g/mol=0

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