SPETROPHOTOMETRIC DETERMINATION OF pH **PLEASE CORRECT IF ANY INFORMATION IS WRO

Question

SPETROPHOTOMETRIC DETERMINATION OF pH

**PLEASE CORRECT IF ANY INFORMATION IS WRONG**

Table 1:

Bromocresol Green standard

BCG mass, g

0.0408

mol weight

720.00

volume of stock solution, mL

500.0

stock conc., mol/L

1.13 x 10-4

Report wavelengths for the maximum absorbance of the acidic form (a) and the maximum absorbance of the basic form (b):

a = 440

b = 620

Complete the following table by reporting the absorbance’s of the two forms for each of these wavelengths.

Table 2: Maximum Absorbance’s

absorbance, A.U.

wavelength a

wavelength b

HIn

0.605

0.117

In-

0.007

1.325

Complete the following table. Insert units in the column headers where appropriate. Report molar absorptivity’s of acid and base forms at the selected wavelengths a and b.

Table 3: Molar absorptivity of HIn and In- and the absorbance’s of the unknown sample

Wavelength

acid form,      

base form,      

Absorbance of unknown,      

a (440nm)

21378

4134

0.215

b (620 nm)

247

46820

0.673

1. Report the [In-]/[HIn] ratio of your unknown solution:

Use Equation Editor to show how you calculated the [In-]/[HIn] ratio.

2. Report the pH of your unknown solution:

Use Equation Editor to show how you calculated the pH.

Table 1:

Bromocresol Green standard

BCG mass, g

0.0408

mol weight

720.00

volume of stock solution, mL

500.0

stock conc., mol/L

1.13 x 10-4

Explanation / Answer

nestly, I'm not quite that handy with this method to calculate the pH. However, I do have a link for you to solve this problem with calculations in every aspect. In that way, you can actually check if you are wrong with a data (So far, all data providen is correct). So here it is, check it and you will solve the questions:

http://www.drcarman.info/9111BC99-0F2F-47DF-A9E4-B516D39373AD/FinalDownload/DownloadId-3209BBE99988BF9A170362FA41AA00D1/9111BC99-0F2F-47DF-A9E4-B516D39373AD/qcalabbk/chap5.pdf

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