Calculate pFe2* at each of the following points in the titration of 25.00 mL of
ID: 923023 • Letter: C
Question
Calculate pFe2* at each of the following points in the titration of 25.00 mL of 0.02281 M Fe2 by 0.03655 M EDTA at a 5.00 pH: (a) 12.50 mL Number pFe2.51951 Incorrect. First, find the conditional formation constant of the Fe-EDTA complex at a 5.00 pH. Confirm in your text that for a 5.00 pH (b) The equivalence point, Ve 4-2.9× 10 7 | and | log(K)= 14.30 Number pFe2+= 116.43 e he coa y muijpyýng hese wo values (c) 19.00 mL Find the formal concentration of FeY by multiplying the dilution factor at Ve = 15.60 mL by the initial concentration of Fe2+ Number pFe 2+ 1110.34 25.00 mL 25.00 mL 15.60 mL (002281 M)Explanation / Answer
(a)
Calculating no of moles of Fe2+ :
= 0.025 L x 0.02281 M Fe +2 = 5.70x10^-4 moles Fe +2
Calculating no of moles of EDTA:
= 0.0125 L x 0.03655 M EDTA = 4.57 x10^-4 moles EDTA
Fe binds EDTA 1:1 ratio
so, 4.57 x10^-4 moles EDTA binds 4.57 x1 0^-4 moles Fe+2 leaving 1.13x10^-4 moles Fe+2 left over
1.13 x10^-4 moles Fe +2 / (0.025 + 0.0125) L = 0.00301 M
pFe +2 = -log (0.00301) = 2.521
(b)
equivalence point, [Fe +2] = [EDTA],
N1V1 = N2V2
0.025*0.02281 = 0.03655*V2
V2 = 15.6 mL
volume EDTA = 15.60 ml
[Fe-EDTA 2-] = (0.025L x 0.02281 M) / 0.0406 L = 0.01404 M
what is the KFe-EDTA?
KFe = 2.1x10^-14, KEDTA at pH5 = 4.83x10^-4
KFe-EDTA = 2.1x10^14 x 4.83x10^-4 = 1.01x10^11
[Fe +2] = (0.0315 / 1.01x10^11)^0.5 = 5.59x10^-7M
pFe +2 = 6.25
(c)
0.019 L x 0.03655 M EDTA = 6.94x10^-4 moles EDTA
0.025 L x 0.02281 M Fe +2 = 5.70x10^-4 moles Fe +2
moles EDTA left over = 1.24x10^-4 moles EDTA
M EDTA = 1.24x10^-4 moles / 0.044 L = 0.00281 M
[Fe +2] = 0.025L x 0.02281 M / 0.044 L = 0.01296 M
K = [Fe+2] / [Fe +2][EDTA]
1.01x10^11 = 0.01296 M / [Fe+2]( 0.00281 M)
[Fe +2] = 4.56 x 10^-11 M
pFe+2 = 10.34
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