Dilution process in spectrophometer

[Serenie]

When using spectrophotometer, to use Rambert-beer's law, we often go through dilution process. Then when measuring neutralization reaction and using week acid or base, then because of water's autoionizaition, i think the results have error.
Is it right?

 

[symbolipoint]

The law relies on the idea that absorbance is a linear relationship to concentration. Ideally, linear, and (I believe) the line crosses the concentration-absorbance plot at the origin.

 

[Borek]

when measuring neutralization reaction

Please elaborate, it is not clear to what you refer here. End point detection of titration, or something else?

 

[symbolipoint]

When using spectrophotometer, to use Rambert-beer's law, we often go through dilution process. Then when measuring neutralization reaction and using week acid or base, then because of water's autoionizaition, i think the results have error.
Is it right?

After reread and thinking about this again, the description is of two usually very separate things: Spectrophotometer to help measure concentration of some dissolved item which absorbs a specified wavelength of visible light; and neutralization titration between acid and base for which endpoint detection would be either by pH-meter, or acid-base indicator compound. These two ideas are usually not related. Maybe you tell what item is being measured?

 

[Serenie]

What i mean is that when doing neutralization titration, we need to measure the concentration. And i want to measure it by spectrophotometer. But when using spectrophotometer, i often need to go through dilution process. Then, while doing the dilution process in the acid solutiton, the concentration may change because of water's autoionizaition.
So what I'm wondering is whether by doing dilution process, the change in concentration (because of autoionization) is trivial enough to ignore.

i'm sorry about my bad english.

 

[Borek]

What i mean is that when doing neutralization titration, we need to measure the concentration.

No, we don't need to detect the concentration, we need to detect the endpoint of the titration. These are two different things.

In general the discussion behind is not very different from the discussion of the end point detection when using one- and two- color indicators. Compare http://www.titrations.info/acid-base-titration-end-point-detection