[VP_JQ]

Hi,

I have the information that a solution 0.06 % w/v of citric acid monohydrate has a pH more or less between 4 and 5. I know this acid has 3 pKa values... How can I know, with calculus, that 0.06 % gives that pH?

Thank you!

[AWK]

For citric acid, K1 and K2 are quite distant from each other, so you can try the approximate calculations like in this link. https://socratic.org/questions/how-do-you-determine-the-ph-of-citric-acid
The actual pH will be around 0.1-0.2 pH unit smaller which is a great accuracy compared to your information.

[VP_JQ]

For citric acid, K1 and K2 are quite distant from each other, so you can try the approximate calculations like in this link. https://socratic.org/questions/how-do-you-determine-the-ph-of-citric-acid
The actual pH will be around 0.1-0.2 pH unit smaller which is a great accuracy compared to your information.

Hi, AWK! Thank you very much for your answer.

I have read the link you've posted. It is exactly what I did yesterday, but if I want adjust pH to 5.5 for example, through the formula pH=-log[H+], I know [H]=3.2exp-6 M, and if I solve in the way that is explain in that page, my % w/v = 6.2exp-5 %. What is the error in my argument? Because you told me that a solution  0.06% in citric acid monohydrate is more or less in the range 4-5.

Greetings!

[AWK]

A pH 5.5 citrate buffer solution is usually made up of citric acid and sodium citrate in an approximate molar ratio of 1:4, or the citric acid is neutralized with sodium hydroxide under pH meter control.

[Babcock_Hall]

In my experience citrate buffers in this range are a challenge to calculate, owing to the effect of ionic strength on the apparent value of the third pK_a.

[VP_JQ]

A pH 5.5 citrate buffer solution is usually made up of citric acid and sodium citrate in an approximate molar ratio of 1:4, or the citric acid is neutralized with sodium hydroxide under pH meter control.

The invention I read utilices 0.06 % of citric acid monohydrate in a formulation for an oral suspension, to adjust pH between 4 and 5. They don't use citric acetate. I made the calculus and I've got a %=6.2x10^-5 % w/v.