Keith Walters's Library tagged → View Popular
08 May 07
Chromic Acid Cleaning Procedure
-
The traditional glassware cleaning solution is "chromic acid", and many
analytical chemistry texts detail the preparation [15,16]. Chromium (VI) is
highly toxic ( mutagenic, carcinogenic ), and disposal is expensive, as all
solutions containing more than 5 mg/l of chromium are considered hazardous
waste in the USA. Disposal of chromic acid requires a two-stage process,
involving bisulfite addition to reduce Cr(VI) to Cr(III), followed by
neutralisation of the acid. There have also been several reports of
spontaneous explosions of chromic acid cleaning solutions [17,18,19],
consequently the use of chromic acid for cleaning glassware is declining,
and several alternative glassware cleaners have recently been evaluated [20].
Sodium dichromate dihydrate is usually used to prepare chromic acid, as
potassium dichromate is less soluble in sulfuric acid. One technique is to
dissolve 140g of technical grade sodium dichromate dihydrate in approximately
100 ml of water. Add two litres of technical grade 98% sulfuric acid to a 4-5
litre glass beaker that is sitting in a cold water bath in a fume cupboard.
Carefully stir the acid gently and pour a few mls of the dichromate solution
slowly into the acid. Keep repeating the addition every few seconds - after
the previous dose has been dispersed. As long as the stirring is gentle and
continuous, little or no splattering should occur, but the solution will
become quite warm. Allow to cool before storing in a glass-stoppered reagent
bottle. Always ensure that the stopper is sufficiently loose to release any
gas pressure. Never use a screw-capped or similar types of sealed containers.
If made correctly, the chromic acid solution should have no precipitate, will
be a deep red colour, and will last for years in a glass-stoppered bottle.
Ensure the glassware to be cleaned does not have any residual organic
solvents. Chromic acid is very effective at around 80C, but an overnight soak
at ambient temperature is commonly used. If the solution develops a green
hue, it is exhausted and should be disposed of, or regenerated, using
appropriate procedures. Slowly pouring used acid down a drain with the cold
water tap fully open is no longer considered appropriate. There is a recent
report of a technique to regenerate chromic acid cleaning solution ( by
distillation of water and oleum ) that reduces disposal quantities [21].
25 Aug 06
Photoluminescence - About.com
-
contactless, nondestructive method of probing the electronic structure of materials
10 Aug 06
JCE Digital Library
- Digital clearinghouse of chemistry demos, question banks, and other material...very useful site, and part of the National Science Digital Library - kwalters00 on 2006-08-10
Anystrem Apreso Software
- Software to capture lecture material and turn into streaming flash content - kwalters00 on 2006-08-10
Chemical Hazards & MSDS
- Information and links to MSDSs and chemical toxicity data - kwalters00 on 2006-08-10
GEMs Home
- Information on green chemistry and how it can be integrated into chemical education. - kwalters00 on 2006-08-10
Chemistry is in the News Website
- Another interesting teaching tool for tying the current news and chemistry together - kwalters00 on 2006-08-10
The Science of Spectroscopy (www.scienceofspectroscopy.info)
- A wiki for all things spectroscopy. Nice articles on the different techniques... - kwalters00 on 2006-08-10
Interactive Web-Based Learning: NMR Spectroscopy
- Who wants to be a millionaire for NMR training! - kwalters00 on 2006-08-10
MERLOT - Multimedia Educational Resource for Learning and Online Teaching
- Compendium of online multimedia educational resources, not just for science! - kwalters00 on 2006-08-10
Calibrated Peer Review
- Calibrated Peer Review tools for implementing it in chemistry courses - kwalters00 on 2006-08-10
Inorganic Chemistry Videos
- Cool videos that can be used to teach inorganic chemistry - kwalters00 on 2006-08-10
03 Aug 06
YouTube - Playing With Thermite
- Caution! Definitely a don't try this at home video, but something to try and convince your science teacher to do. - kwalters00 on 2006-08-03
Selected Tags
Related Tags
Sponsored Links
Ads by Google
Top Contributors
Groups interested in chemistry
Related Lists on Diigo
-
Science Resources
A list of resources for Sci...
Items: 115 | Visits: 104
Created by: Dianne Krause
-
Chemistry
This sites are related to t...
Items: 262 | Visits: 112
Created by: Alison Hapka
-
Web Seminar: Chemistry: Water
Resources from the NSDL Web...
Items: 19 | Visits: 98
Created by: nsdl workshops
Diigo is about better ways to research, share and collaborate on information. Learn more »
Join Diigo
