Determining the Highest pH for Acid Solutions

[sp3sp2sp]

Homework Statement

I am just a little confused about how the question is worded. It asks:
Which of the following solutions would have the highest pH? Assume that they are all
0.10 M in acid at 25 C. The acid is followed by its Ka value.
the bolded is what I don't understand. I don't know what they mean by "in acid" ? thanks for any help

Homework Equations

The Attempt at a Solution

 

[mjc123]

That means the analytical cocentration of the acid is 0.10M. That is, the solution is the result of dissolving 0.1 moles of the acid in 1L of water. Actually, the acid will be partly dissociated, so the true concentration of the acid form will be less than 0.1 M. So if you had 0.1 moles of acetic acid (AcOH) in water, you would have some undissociated AcOH and some dissociated H⁺ and AcO^-. The total concentration of AcOH and AcO^- would be 0.1 M, and that is what the question refers to.

 

[symbolipoint]

The values for pK_a come from the acids' K_a values. The "p" part of the constant means, "negative logarithm of...".

Two specific examples:
Acetic Acid, K_a=1.8*10^(-5), pK_a=4.756, weak monoprotic acid
Oxalic Acid, K_a1=5.37*10^(-2), pK_a1=1.27, diprotic acid, not so weak compared to Acetic

Each if dissolved to the same molarity will show less acidic for Acetic than for Oxalic; Meaning LOWER pH for Acetic than for the stronger Oxalic.
The Acetic Acid solution will have the higher pH, of the two solutions. You can make your predictions using the pK_a values or using the K_a values. Higher pKa, higher pH of the acid in solution, lower acidity in solution