Table 12-1 Activity coefficients for aqueous solutions at 25°C\" Ion size Ionic
ID: 557920 • Letter: T
Question
Table 12-1 Activity coefficients for aqueous solutions at 25°C" Ion size Ionic strength ( M) Ion (, pm) 0.001 0.005 0.01 0.05 0.1 Activity coefficient () 9000.967 0.933 0.914 0.86 0.83 8000.966 0.931 0.912 0.85 0.82 7000.965 0.930 0.909 0.845 0.81 Charge (z) = ±1 CH-CHCH2C0%, (CHJ2CHCH2C0%, (CH,CHJ4N+, (C3H7)2NH3 600 0.965 0.929 0.907 0.835 0.80 500 0.964 0.928 0.904 0.83 0.79 Co(NH3)4(NO2):, CH3C0%, CICH2C0%, (CH3)4N (CH3CH2)2NH2, H2NCH2CO2 H3NCH CO,H, (CH3)3NH+, CH3CH2NH3 OH , F , SCN", OCN , HS , ClO3, CIO4, BrO3, IO4, MnO4, HCO7, H2citrate, CHzNHj, (CH32NHz K, Cl, Br , I, CN, NO2, NO3 Rbf, Cs*, NH, TI, Ag 450 0.964 0.928 0.902 0.82 0.775 400 0.964 0.927 0.901 0.815 0.77 350 0.964 0.926 0.900 0.81 0.76 300 0.964 0.925 0.899 0.805 0.755 250 0.964 0.924 0.898 0.80 0.75 Activity coefficient (Y) 800 0.872 0.755 0.69 0.52 0.45 7000.872 0.755 0.685 0.50 0.425 Charge (z) = ±2 Mg2*, Be2+ Ca2+, Cu2+, Zn2+, Sn2+, Mn2+, Fe2+, Ni2+, Co2+, c,H(CO22 6000.870 0.749 0.675 0.485 0.40:5 Sr*, Ba2+, Cd2+, Hg2+, S2-, S,O2 , woi, H,C(CO2)2 (CH2CO22, (CHOHCO2)2 500 0.868 0.744 0.67 0.465 0.38 Hcitrate 450 0.867 0.742 0.665 0.455 0.37 400 0.867 0.740 0.660 0.445 0.355Explanation / Answer
Determine the activity coefficient for Fe2+ ions in a solution with an ionic strength of 0.020 M.
First
IS = 0.02 M is not found in the table; therefore apply Debye Huckel equation
Activity of X = x * [X]
Where:
Activity coefficient () of “x”
[X] = molar concentration concentration of X
Note that Activity coefficient () depends on
Recall that:
-log() = 0.51*(Zi^2)*sqrt(I.S.) / ( 1 + ( * sqrt(I.S)/305))
Where
i = activity coefficient for species “i”
i = theoretical diameter in pm (10^-12 m)
Zi = Charge of ion
I.S. = ionic Strength (usually used as as well)
alpha for Fe+2 =600 pm, Z = +2; IS = 0.02
-log(-Fe+2) = 0.51*(2^2)*sqrt(0.02) / ( 1 + (600 * sqrt(0.02)/305))
-Fe+2 exp(-0.2257) = 0.79795
-Fe+2 = 0.79795
which makes sense since it is btween 0.87 and 0.749 ( table)
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