Which method, gravimetric analysis or volumetric analysis is more reliable and why?

Question

I am looking at these methods used to determine metal content in a solution.

Answer 1

The previous responder brings up excellent points, particularly about the method relying on how good the analyst is. This is highly true! However I would add, that gravimetric methods are typically more ACCURATE for the following reasons:

1. Errors associated with volume measurement (loss in transfer, parallax, spillage, over-titration, etc.) are reduced in gravimetric measurements. In most gravimetric measurements, you WEIGH a final product, which either IS the compound of interest, or is stoichiometrically related to it.

2. Gravimetric methods are less sensitive to temperature than volumetric methods.

3. While BOTH types of methods are subject to sample loss, gravimetic methods are less so. (Note: This is less true if the analyst is a clutz. Goes very well with the previous poster's comment!)

4. A mass is easier to reproducibly determine than a concentration. (Any day of the week!)

5. A mass is easier to STANDARDIZE than a concentration. Again there are errors associated with both, we concede, but mass is generally easier to deal with.

6. You will more likely encounter limits (of sensitivity) in volume measurements than you will in mass measurements, depending on how your lab is equipped.

These are a few thoughts, I'm sure there are others.

Answer 2

Frankly, in real world chemistry the water would be acified with aqua regia and then run on an analytical instrument known as an atomic spectrophotometer. It vaporizes and ionizes the sample and detects the presence of any lead plasma in the sample by comparing the spectrum of the sample plasma against a special tube which generates the spectral lines characteristic of lead plasma. The two light beams are combined, and if lead ions are present in the sample plasma, they absorb some of the energy from the lead reference tube. The decrease in energy is porportional to the concentration of lead ions. This technique is accurate to several parts per billion on a good instrument. However, this is an achedemic setting ............. I'm making the assumption "gravimetric" has to do with generating a precipitate and "volumetric" has to do with some sort of titration. If I were forced to practice 19th century chemistry, I might choose gravimetric analysis. This is because lead is a heavy metal and forms insoluable salts with very low soluabilities. The only really soluable salt is the acetate and the nitrate. Chlorides, hydroxides, carbonates, sulfates and oxides are quite insoluable. There might be some problems if the levels of lead are very low, a 12 PPM lead sample would only precipitate about 3 micrograms of PbCl2 per liter. I doubt an analytical balance could measure this. Volumetric analysis would probably be something similar to the Volkhart salt test. This is a competative reaction between silver chloride and a highly colored Iron complex. Again, this test is accurate in terms of parts per hundred and anything lower than this would probably not give accurate answers. Hence, both gravimetric and volumetric analysis of Lead are probably not possible if the concentration is less then 0.1%. This is why working chemists use the sophisticated kinds of instruments they do.

Answer 3

oh that depends! there are some very good gravimetric methods for metals...and some very good volumetric ones. In part it depends on the amount of metal you are trying to determine, in part it depends on which metal it is ....and always it depends on how good the analyst is! There are so many sources of error (each piece of glassware, the balance, side reactions or contaminants and so on) that it's difficult to answer!

Answer 4

I'D SAY VOLUMETRIC BECAUSE OF THE MOLECULAR STUCTURE OF THE SOLVANT IS MORE DENSE