Question

To obtain the best separation of two weak acids in capillary electrophoresis, it makes sense to use the pH at which their charge difference is greatest. Prepare a spreadsheet to examine the charges of malonic and phthalic acid as a function of pH. At what pH is the difference greatest?

Short answer

The greatest value of pH = 5.55

Step-by-step solution

Define Function of  pH

PH is the measure of how acidic or basic a substance is. In humans, pH balance plays a role in keeping the body functioning optimally. The ideal pH of the body is slightly alkaline, which facilitates certain biochemical reactions like oxygenating the blood.

Malonic and phthalic acid

	A	B	C	D	E	F	G	H	I	J
1	Malonic			$\alpha$	$\alpha$	$\alpha$	$\alpha$	av.charge	av.charge	charge
2	K1 =	pH	$\left[H^{+}\right]$	$\left[H{M}^{-}\right]$	$M^{2-}$	$H{P}^{-}$	$P^{2-}$	malonate	phtalate	difference
3	1.42E - 03	5.52	3.0E - 06	0.600	0.399	0.436	0.563	-1.398	- 1.562	- 0.1639
4	K2 =	5.53	3.0E - 06	0.594	0.405	0.430	0.569	- 1.403	- 1.567	- 0.1640
5	2.01E - 06	5.54	2.9E - 06	0.589	0.410	0.425	0.574	- 1.409	- 1.573	- 0.1641
6	phthalic	5.55	2.8E - 06	0.583	0.416	0.419	0.580	- 1.415	- 1.579	- 0.1642
7	K1 =	5.56	2.8E - 06	0.577	0.421	0.413	0.585	- 1.420	- 1.584	- 0.1642
8	1.12E - 03	5.57	2.7E - 06	0.572	0.427	0.408	0.591	- 1.426	- 1.590	- 0.1641
9	K2 =	5.58	2.6E - 06	0.566	0.433	0.402	0.597	- 1.432	- 1.596	- 0.1640
10	3.90E - 06	5.59	2.6E - 06	0.561	0.438	0.397	0.602	- 1.437	- 1.601	- 0.1639

Maximum difference

From spreadsheet, the greatest value of pH = 5.55