[istrydummy]

1)How do you determine the concentration of (say) ammonia or Uric acid in an experimental sample if the colour produced during analysis is:

a) darker than that produced by the strongest standard solution?

My answer: Do you Dilute the sample appropriately?

b)lighter than than that from the weakest standard solution?

My answer: Do you make up more concentrated  standards?

2) Why do you insert a blue filter in the colorimeter when using Nessler's reagent but a red filter when using benedict's (uric acid) reagent?

My answer: Does it have something to do with the wavelnegths of the reagents?

Would appreciated if you can explain these problems to me... Thank you for your time.

[aHerraez]

1a) Yes, you must dilute the sample and repeat the assay (diluting the product of the assay is not correct).

1b) makes no sense: if you use more concentrated standards, you will get yet darker products. You need less concentrated standards (aasuming your sample cannot be less diluted).

2) Yes, it has to do with the spectra of the products, not the reagents. I don't know these reactions, but the filter should be adequate to let pass just the color of the product. A red filter will let pass wavelengths in the red, so it's good for blue-violet products, and so on.
If the colorimeter needs to use filter is because it emits too much light in the nonuseful wavelengths. Otherwise, you could measure without any filters.