1. Iterates through a range of volumes (incrementally add small volumes of NaOH)-this should be done by adding 6 ml of NAOH . Document Preview: ENG3103 Engineering Problem Solving Computations Semester 2, 2013 Page 1 of 3 Assessment: Assignment 1 Due: 12 August 2013 Marks: 100 Value: 10 % Introduction Acetic acid is contained in a 100 mL aqueous solution with concentration [CH3CO2H] = 0.5 M (where 1 M = 1 mole/L). The (reversible) chemical reaction for acetic acid is: 3 2 3 2 CH CO H CH CO H ? ? ? (1) and the equilibrium conditions are: ? ? 3 2 3 2 CH CO H CH CO H p log aa a KK K ? ? ?? ?? ?? ?? ?? ? (2) where pKa = 4.756 for acetic acid in water. The pH pH log H? ? ? ?? ?? (3) and concentrations of all species can be determined for the acetic acid solution from Eq. (2) by noting that initially: ? ? 3 2 3 2 3 2 CH CO H CH CO 0.5M H CH CO ?? ? ? ?? ?? ? ?? ?? ? ?? ?? The titrant sodium hydroxide (with concentration [NaOH] = 0.1 M) is slowly added to the acetic acid solution. Every mole of NaOH that is added produces one mole of Na+ and one mole of OH and each mole of OH consumes one mole of H+. This equation is blank for consistency with the original document (4) The concentration of any species is given by (V is volume): ? ? X X added initial N V V ? ? (5) The effect of H+ being consumed by OH is that the equilibrium of Eq. (2) is disturbed and a new equilibrium must be formed. Let dC be the change in concentration caused by addition of dV litres of titrant, then the new concentrations that satisfy Eq. (2) can be obtained by solving for dC: ? ?? ? ?? ? ? 3 2 3 2 3 2 CH CO H NaOH 3 2 CH CO H CH CO H CH CO H a dC dC dC K dC ? ? ? ? ?? ?? ? ?? ?? ? ? ? ? (6) Note that Eq. (1) defines a relationship between the dC values: 3 2 3 2 CH CO H CH CO H dC dC dC ? ? ? ? ? (7) and because the reaction is forward, then dCH+ should be positive. The equivalence point is where the number of moles of base is equal to the number of moles of acid. Above the equivalence point, a different chemical reaction occurs because all of the H+ has been consumed: ENG3103 Engineering Problem Solving Computations Semester 2, 2013 Page Attachments: assignment-1.pdf