The Big Problem!! There has been a major accident at the Hairum Scairum Costume
ID: 931851 • Letter: T
Question
The Big Problem!! There has been a major accident at the Hairum Scairum Costume Hair Company. Due to an explosion in the hair dye line, several tanks were overturned, spilling their solutions which seep out into the soil and into the pond (with a nice fountain and plastic flamingos in it) that is in front of the headquarters building. The Fire department puts out the fire and now it’s time for the clean up to begin. The company calls in the world-famous consulting chemists, Cornelius and Cordelia, to help them figure out what to do. You are part of their consulting company and are assigned the following problems to solve. Warning! Cornelius and Cordelia are sticklers for good use of sig figs and always expect you to define your assumptions. 1) One of the major problems is the large amount of phthalic acid (see your text for Ka's) managed to make its way into the pond. The Company wants to know the pH of the pond. Cornelius makes some quick measurements and finds the pond is perfectly circular and has a radius of 1.000 meter and a depth of 1.000 meter. (Remember that 1 mL = 1 cm3). The tank that held the phthalic acid was a 3.00 L tank. The concentration in the tank was 3.000M. A) What is the formal concentration, (HA)0 , in the pond if all of the phthalic acid solution is added? B) What would the pH of the pond be, assuming there are no other acid/base species present except the phthalic acid? C) What would the fraction of the three different acid species (HA, HA- and A2-) be in solution at that pH? 2) Another problem is the large amount of Titanium and Cobalt in the vats that spilled. A) Calculate the Kf' values for titanium and cobalt with EDTA at the pH of the pond calculated in question #1. You may round the value of the pH to make life easier. B) You are instructed to find out how much of each metal is in the pond (concentration). Describe, based on your knowledge of EDTA titrations, how you would go about analyzing for these two metals. Note that they both exist in the solution at the same time.
Explanation / Answer
A ) Calculations for For [HA]0 -
Apply the relation M1 V1 = M2 V2
M (unknown ) x 3..1428 x !0^9 = 3.000 x 3
M ( unknown ) = 2.86 x 10^--9 M
note volume of tank = 3.1428 x 1000 x1000x 1000 = 3.1428 x 10^9 m^ 3
_For B) Given pKa of phthalic acid = pKa1 = 2.89 & pKa2 = 5.59
hence calculate Ka1 & Ka2 separately - using relation - pk = -log Ka
Ka1 = 1.29 x 10^-3
Ka2 = 2.57 x 10^-6
Calculate [H^+ ] using Ka1, as Ka1 is much larger than Ka2
Since phthalic acid is a weak acid its degree of dissociation can be given using Odtwald's dilution law-
alpha = SQRT (Ka1 /c) where c represents concentration of the acid solution
substituting we get , alpha = SQRT (1.29 x 10 ^-3 / 2.86 x 10^-9)
alpha = 0.67 x 10^3
alpha represents the degree of dissociation of the acid and also its {H^+] as the acid ionizes according to eqn.
H2 Phth -----------> H^+ + HPhth ^- -----------------------------------------------------------( Ka1 = 1.86 x 10^-3 )
HPhth ^- ------------> H^+ + Phth^- ---------------------------------------------------------( Ka2 = 2.57 x 10^-6 )
Now, find out pH using the [H^+] pH = -log [H^+ ]
pH = - log ( 1.86 x 10^-3 )
= 2.73
C) [ HA ] = 2.86 x 10^-9 (1 - 0.67 X10^-3 ) M
[ H^+] = 1.86 x !0^-6 M = [ HA^- ] = [ A^- ]
It is noteworthy that phthalic acid is a weak dibasic acid where Ka1 is much larger than Ka2 , hence the second ionization of HA^- would not contribute significantly to [H^+ ] or [ A^2- ] & can be ignored.
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*Please note that the other question refers to concentrations of titanium &cobalt which is not available in this posted question. Please post the question separately as a fresh question with desired details. Happy to help.
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