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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: hjjou on July 08, 2004, 01:41:36 PM

Title: pH for binary acid soultion
Post by: hjjou on July 08, 2004, 01:41:36 PM

Hi,
I would like to know what euation I should use when I am try to calculating the pH of a binary acid soultion (e.g. a mixture solution with acetic and lactic).  For a simple acid solution, I can use the equation pH=pKa+log[A-]/[HA], what I don't quite clear is how can I calculate the pH or concentration of a more complicated solution like binary acids system with known pkas for the acids.  Thanks for any input.

Title: Re:pH for binary acid soultion
Post by: Donaldson Tan on July 08, 2004, 01:51:28 PM

Simultaneous Equations.

Title: Re:pH for binary acid soultion
Post by: hjjou on July 08, 2004, 01:57:42 PM

To Geodome:

Thanks for replying.  What are Simultaneous Equations?  I am not a Chemistry student, this is work related.  Can you explain a little more or refer me to any literature?  Thanks.

Title: Re:pH for binary acid soultion
Post by: AWK on July 09, 2004, 04:38:32 AM

For weak acid solution
pH= -log(SQRT(Ka x c))
For mixture of a few weak acids
pH=-log(SQRT(K₁ x c₁ + K₂ x c₂ + ...))

Your equation is used for buffer solutions.

Title: Re:pH for binary acid soultion
Post by: hjjou on July 09, 2004, 09:17:22 AM

To AWK:

Thanks so much.

So I used the wrong equation?

Is there a textbook or literature I can read?

Title: Re:pH for binary acid soultion
Post by: AWK on July 12, 2004, 04:11:11 AM

Your eqaution is true but useless for pH calculation of weak acid because it contains two unknown variables.

read on weak acids in university textbooks on general or physical chemistry