ANALYTICAL CHEMISTRY TUTORIAL 3

Kusniar Deny Permana

kusniardenypermana@gmail.com

01115639556

At the maximum absorption band, the transmittance is only 5.00%. What is the corresponding absorbance?

2

1

3

1

TA %log2

699.0A5log2A

a. What value of absorbance corresponds to 45 % T?

b. If a 0.01 M solution exhibits 45 % T at some wavelength, what will be the % T for a 0.02 M solution of the same substance?

4

2

What value of absorbance corresponds to 45 % T?

5

2a

TA %log2

45log2A

437.0A

6

2b

bcA

c

Ab

Same substance & cuvet

bbb 2211

2

2

1

1

c

A

c

A

1

1

22 A

c

cA

347.001.0

02.02 A

694.02 A

TA %log2

AT 2%log

694.02%log T

306.1%log T

%23.20% T

Chloroaniline in a sample is determined as the amine picrate. A 0.0265 g sample is reacted with picric acid and diluted to 1.00 L. The solution exhibits an absorbance of 0.368 in a 1.00 cm cell. What is the % chloroaniline in the sample? (Given: MW of Chloroaniline = 127.6 g/mol, = 1.25 x 104cm-1mol-1L)

7

3

8

3

bcA

b

Ac

11025.1

368.04 xx

c

Mxc 510944.2

The reaction is 1:1:1

TEAMINEPICRAmolinechloroanilmol

LxLmolxinechloroanilmol 1/10944.2 5

molxinechloroanilmol 510944.2

MWxmolxinechloroanilmass 510944.2 molgxmolxinechloroanilmass /6.12710944.2 5

gxinechloroanilmass 3108.3

%1000265.0

108.3%

3

xgx

inechloroanil

%34.14% inechloroanil

a. A 3.96 x 10-4 M solution of compound A exhibited an absorbance of 0.624 at 238 nm in a 1.00 cm cuvet; a blank solution containing only solvent has an absorbance of 0.0290 at the same wavelength. Find the molar absorbtivity of compound A.

b. The absorbance of an unknown solution of compound A in the same solvent and cuvet was 0.375 at 238 nm. Find the concentration of A in the unknown.

c. A concentrated solution of compound A in the same solvent was diluted form an initial volume of 2.00 mL to a final volume of 25.0 mL and then had an absorbance of 0.733. What is the concentration of A in the concentrated solution?

9

4

10

4a

A

c

y=mx+C

A=(b)c+C

The slope is b

01096.3

0290.0624.04

12

12

xxx

yyb

1

453.1502

1096.3

595.0 M

xb

111

53.15021

53.1502

cmMcm

M

b

b

Lcmmolx 113105.1

(x2,y2)

(x1,y1)

x1=0; x2=3.6x10-4;

y1=0.0290; y2=0.624

The equation for calibration curve

11

4b

Cmxy

029.0)105.1( 3 Xxy

375.0, yunknown

029.0)105.1(375.0 3 Xx

MxX 41031.2

The equation for calibration curve

12

4c

029.0)105.1( 3 Xxy

733.0, ysample

029.0)105.1(733.0 3 Xx

MxX 410693.4

LxmL

mLxMxmLAmol 11000

2510693.4)25( 4

molxmLAmol 510173.1)25(

LxmL

mL

molxmLAionconcentrat

11000

2

10173.1)5(

5

MxmLAionconcentrat 310865.5)5(