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Q: Chemistry: Spectophotometric analysis ( No Answer,   1 Comment )
Question  
Subject: Chemistry: Spectophotometric analysis
Category: Science > Chemistry
Asked by: uncross-ga
List Price: $30.00
Posted: 04 Sep 2004 14:18 PDT
Expires: 04 Oct 2004 14:18 PDT
Question ID: 396874
Show me how to calculate these? And the answers?:

What are the bromophenol blue concentrations in a mixture of the
following reagents measurements?

0.10M Citrate Buffer pH = 2.4 (5.00mL) and 1.5E-04M Bromophenol Blue (0.00mL)
0.10M Citrate Buffer pH = 2.4 (4.50mL) and 1.5E-04M Bromophenol Blue (0.50mL)
0.10M Citrate Buffer pH = 2.4 (4.00mL) and 1.5E-04M Bromophenol Blue (1.00mL)
0.10M Citrate Buffer pH = 2.4 (3.00mL) and 1.5E-04M Bromophenol Blue (2.00mL)
0.10M Citrate Buffer pH = 2.4 (2.00mL) and 1.5E-04M Bromophenol Blue (3.00mL) 
0.10M Citrate Buffer pH = 2.4 (1.00mL) and 1.5E-04M Bromophenol Blue (4.00mL)
0.10M Citrate Buffer pH = 2.4 (0.00mL) and 1.5E-04M Bromophenol Blue (5.00mL)
Answer  
There is no answer at this time.

Comments  
Subject: Re: Chemistry: Spectophotometric analysis
From: nanoalchemist-ga on 07 Sep 2004 10:08 PDT
 
Looks like you're doing a standard addition/ calibration curve. The
easy way to calculate this, since you're already in M is to use

M1V1 = M2V2

where the Ms are Molarities, and V volumes

Rearange to get M2

M2= M1V1 / V2 

The volume units will cancel leaving you units of M, which you want.

Fortunatly for you, V2 is a constant 5 ml, and M1 is also constant
(1.5 E-4 M), you then have

M2 = (1.4 E-4 M)*V1  / 5 ml

Thus, for your examples

1)  M2 = (1.4 E-4 M)*0 ml  / 5 ml  = 0 M
2) M2 =  (1.4 E-4 M)*0.5 ml  / 5 ml = 1.4 E-5 M 
.
.  (etc)
.
7) M2 =  (1.4 E-4 M)*5 ml  / 5 ml = 1.4 E-4 M

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