# Tag Info

## New answers tagged analytical-chemistry

1

These are the absorbance spectra of copper sulfate in water (open markers) and heavy water (filled markers) (1): The absorbance in water is maximum at 780 nm, as stated in the reference. From the spectrum, the molal absorption coefficient, at 780 nm, appears to be approximately 12.5 $\mathrm{(mol/55.51 mol \ of \ water)^{-1} cm^{-1}}$ with aquamolality ...

2

Answering this question requires a preliminary discussion of the solubility product constants of three silver halides and the formation constants of three silver complexes. First, note that $\ce{AgCl}$, $\ce{AgBr}$, and $\ce{AgI}$ are all insoluble in water, but insoluble is a relative term in the end. Their respective solubility equilibria and solubility ...

2

The last time I calibrated an absorbance spectrometer, it was one I made from parts (for an undergraduate Instrumental Analysis teaching laboratory) and I used a 0.0509 M holmium chloride solution I prepared. The visible region spectrum I obtained is here: Holmium solutions are well known as UV-Vis calibration standards and you can purchase from, e.g., www....

3

Your dilution approach can be heavily improved. Rule no. 1: 2+2 $\neq$4 in solution preparation from an analytical chemist's perspective. An extreme example is that you add 50 mL of water+50 mL of ethanol $\neq$ 100 mL solution. If you add a solid NaCl to 1 L of water, the volume may not remain 1 L. It may decrease! Analytical dilutions are always ...

2

I did the experiment. My buffer was a commercial product a simple packet of salts probably phthalate based. I made it up in deionised water to the right volume then measured its pH with a simple all-in-one probe-meter I measured the buffer neat and then again after 1/5 serial dilutions. I rinsed the probe with deionised water between readings. The pH fell ...

2

Since you have identified your unknown as salicylic acid (2-hydroxybenzoic acid), I'd help you understand how easily understand the substituents of aromatic nucleus induce shielding-deshielding effects. The following diagram illustrate the $\mathrm{^1H}$-$\mathrm{NMR}$ assignments of salicylic aromatic protons: A lot of experts do not like explaining ...

4

The statement is not 100% correct. Ordinary mass spectrometry will not give you exact masses to 5 or 6 decimal places, say, m/z 415.14 for a singly charged molecular ion. Now there will be hundreds of compounds with this mass. On the other hand HRMS gives you a accurate and precise mass say 415.14509. This detailed number drastically reduces the number of ...

1

Fluorescin(left), a non-fluorescent compound, reacts with iron in residual blood samples to produce highly fluorescent fluorescein(right). The reference$\ce{^{[2]}}$ from which the following excerpt is taken describes the chemistry, preparation of reagents, and application to forensics. Fluorescin is the oxidized colorless form of fluorescein. Fluorescin ...

Top 50 recent answers are included