REPORT SHEET Determination of the Solubility-Product Constant for a Sparingly So
ID: 1043580 • Letter: R
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REPORT SHEET Determination of the Solubility-Product Constant for a Sparingly Soluble Salt A. Preparation of a Calibration Curve Initial [CrO Volume of 0.0024 M K2CrO Total volume 160 ?12X 3. Molar absorption coefficient for [Cro, .0267 Average molar absorption coefficient Standard deviation (show calculations) 512 B. Determination of the Solubility-Product Constant co, L4g1 K,p of Ag CrOs Absorbance 1. 43 2. 42. 2. 42. .3 Copyright C 2012 Pearson Education, Inc. axis should be label(Cro2) x 104 notExplanation / Answer
The callibration curve is plotted between Absorbance of standard solutions of known concentrations(C)
Using Beer's law ,
Absorbance=e*l*C
where e=absorptivity of species(CrO42-)
l=path length of light(1 cm)
A callibration curve between Abs and concentration is linear of the form y=mx+c,
y=Abs ,x=concentration ,m=slope=el
given: slope=el=0.0207
for l=1 cm
e=0.0207 M^-1
or e can be calculated using equation,e=Abs/(concentration of known standard)*l
1) std 1) C=0.0024M*(1ml/100ml)=2.4*10^-5M
e=93.3/(2.4*10^-5M) (1cm)=3887500 cm^-1M^-1
2)std 2) C=0.0024M*(10ml/100ml)=2.4*10^-4M
e=92.8/(2.4*10^-4M) (1cm)=386666.7cm^-1M^-1
3)std 3) C=0.0024M*(15ml/100ml)=3.6*10^-4M
e=83.0/(3.6*10^-4M) (1cm)=230555.5 cm^-1M^-1
4)std 4) C=0.0024M*(20ml/100ml)=4.8*10^-4M
e=89.3/(4.8*10^-4M) (1cm)=186041.7 cm^-1M^-1
Average e=(3887500+386666.7+230555.5+186041.7 )/4=1172691.0 cm^-1M^-1
Std dev=(summation(x-x(average))^2/N)^0.5 ,N=number of data=4
So, std dev=((3887500-1172691.0)^2+(386666.7-1172691.0)^2+(230555.5-1172691.0)^2+(186041.7-1172691.0)^2 )/4)^0.5=1569165.243
Now ,for unknown solutions C=[CrO42-] can be calculated using equation ,
C=Absorbance/e
1)C=[CrO42-]=93.0/1172691.0 M^-1=7.930*10^-4M
Ksp(Ag2CrO4)=[Ag+]^2 [CrO42-]
Also [Ag+]=2[CrO42-]=2*(7.930*10^-4M)=1.586*10^-3M
Ksp=(1.586*10^-3M)^2(7.930*10^-4M)=1.995*10^-9
2)C=[CrO42-]=92.1/1172691.0 M^-1=7.854*10^-4M
[Ag+]=2[CrO42-]=2*(7.854*10^-4M)
Ksp=(2*7.854*10^-4M)^2 (7.854*10^-4M)=1.937*10^-9
3)C=[CrO42-]=89.3/1172691.0 M^-1=7.614*10^-4M
[Ag+]=2[CrO42-]=2*(7.614*10^-4M)
Ksp=(2*7.614*10^-4M)^2 (7.614*10^-4M)=1.766*10^-9
Average Ksp=((1.766*10^-9)+(1.937*10^-9)+(1.995*10^-9))/3=1.899*10^-9
Std dev=(((1.766*10^-9)-(1.899*10^-9))^2+((1.937*10^-9)-(1.899*10^-9)^2+((1.995*10^-9)-(1.899*10^-9)^2)/3)^0.5=9.721*10^-11
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