Chemistry Labs

Problem 1

A damaged label on an acid bottle. The label on a bottle containing a dilute aqueous solution of an acid became damaged so that only its concentration was readable. A pH meter showed that the hydrogen-ion concentration was equal to the value on the label ([HX+]=c[\ce{H+}] = c). (1.1) Give the formulae of four acids that could have been in the solution if the pH changed by one unit after a tenfold dilution. (1.2) Could it be possible that the dilute solution contained sulfuric acid (pKa2=1.99pK_{a2} = 1.99)? Answer Yes or No; if yes, calculate or estimate the pH. (1.3) Could it be possible that the solution contained acetic acid (pKa=4.76pK_a = 4.76)? Answer Yes or No; if yes, calculate or estimate the pH. (1.4) Could it be possible that the solution contained EDTA (ethylenediaminetetraacetic acid; pKa1=1.70pK_{a1} = 1.70, pKa2=2.60pK_{a2} = 2.60, pKa3=6.30pK_{a3} = 6.30, pKa4=10.60pK_{a4} = 10.60)? Answer Yes or No; if yes, calculate the concentration.
Step 2 of 4: Sulfuric acid check
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[HX+]=c+[SOX4X2−]>c  ⇒  Sulfuric acid: No[\ce{H+}] = c + [\ce{SO4^{2-}}] > c \;\Rightarrow\; \text{Sulfuric acid: No}
Analysis

Sulfuric acid dissociates completely in its first step, yielding cc mol L−1^{-1} of HX+\ce{H+}; the second dissociation HSOX4X−⇌HX++SOX4X2−\ce{HSO4- <=> H+ + SO4^{2-}} necessarily produces additional HX+\ce{H+}, so [HX+]=c+[SOX4X2−]>c[\ce{H+}] = c + [\ce{SO4^{2-}}] > c always. Answer: No.