International Chemistry Olympiad · 2008

Problems

Problem 1A 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 ( $[\ce{H+}] = c$ ). (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 ( $pK_{a2} = 1.99$ )? Answer Yes or No; if yes, calculate or estimate the pH. (1.3) Could it be possible that the solution contained acetic acid ( $pK_a = 4.76$ )? Answer Yes or No; if yes, calculate or estimate the pH. (1.4) Could it be possible that the solution contained EDTA (ethylenediaminetetraacetic acid; $pK_{a1} = 1.70$ , $pK_{a2} = 2.60$ , $pK_{a3} = 6.30$ , $pK_{a4} = 10.60$ )? Answer Yes or No; if yes, calculate the concentration.Solutions: 1