Q19.151 CP - Chemistry: Molecular Nature Of Matter And Change

Question

Buffers that are based on 3-morpholinopropanesulfonic acid (MOPS) are often used in RNA analysis. The useful pH range of a MOPS buffer is $\mathbf{6}\mathbf{.}\mathbf{5}$ to $\mathbf{7}\mathbf{.}\mathbf{9}$. Estimate the ${\mathbf{K}}_{\mathbf{a}}$of MOPS.

Step-by-Step Solution

Answer

The value of MOPS is $6\times {10}^{-8}$.

Step 1: Definition of Concept.

Capacity: The amount of heat energy required to raise the temperature of a body by a certain amount is known as heat capacity. The amount of heat in joules required to raise the temperature 1 Kelvin is known as heat capacity (symbol: C) in SI units.

 

Step 2: Calculate the K a of MOPS.

Considering the given information:

The pH range of 3-morpholinepropanesulfonic acid (MOPS) is $6.5$ to$7.9$.

From the given pH range, calculate the average ${\text{pK}}_a$.

Average ${\text{pK}}_a$(center of range)

$$\begin{gathered} =(7.9+6.5)/2 \\ =7.2 \end{gathered}$$

                                                                   

Calculate the ${\text{K}}_a$ value from ${\text{pK}}_a$value,

Average ${\text{pK}}_a\text{=7.2}$ 

$\begin{array}{c}{\mathrm{K}}_{\mathrm{a}}={10}^{-7.2}\\ =6.3095734\times {10}^{-8}\\ =6\times {10}^{-8}.\end{array}$

Therefore, the ${\mathrm{K}}_a$ value of MOPS is $6\times {10}^{-8}$.