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Chapter 19: Q19.108P (page 876)

Tris (hydroxymethyl)aminomethane [(HOCH2)3CNH2,known as TRIS] is a weak base used in biochemical experiments to make buffer solutions in the pHrange of 7 to 9. A certain TRIS buffer has a pHof8.10at25掳Cand a pHof7.8at37掳C.Why does the pH pH change with temperature?

Short Answer

Expert verified

In order to solve this problem, we have to remember that every chemical reaction has its equilibrium constant K, which changes as the temperature change.

We know that, when we have a buffer, the Ka value is included in the Henderson-Hasselbalch equation, thus, when the Ka value changes, the pH value also changes:

pH=pKa+logA-[HA]

Step by step solution

01

Concept introduction

Tris(hydroxymethyl)aminomethane, sometimes known as tromethamine or THAM in medicinal settings, is an organic molecule with the formula (HOCH2)3CNH2.

02

Explanation

In order to solve this problem, we have to remember that every chemical reaction has its equilibrium constant K, which changes as the temperature change.

If the reaction is exothermic:

- Temperature increases, K value decreases

- Temperature decreases, K value increases

If the reaction is endothermic:

- Temperature increases, K value increases

- Temperature decreases, K value decreases

We know that, when we have a buffer, the Ka value is included in the Henderson-Hasselbalch equation, thus, when the Ka value changes, the pH value also changes.

pH=-logKa+logA-[HA].

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Most popular questions from this chapter

A biochemist needs a medium for acid-producing bacteria. The pH of the medium must not change by more than 0.05pHunits for every0.0010molofH3O+generated by the organisms per litre of medium. A buffer consisting of0.10MHAand0.10MA-is included in the medium to control itspH. What volume of this buffer must be included in1.0Lof medium?

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