Talk:Concentration
My first effort at wikipedia, the last paragraph still needs work I think. Let me know what you think. Aglimme
Sorry, my english is too bad to correct the article, however I signal that molarity and normality are different and distinct concepts. Svante 23:48, 3 Jul 2004 (UTC)
Today I expanded this article significantly, adding a table, image, further examples, etc. I still feel it needs some work - in particular, the definition of "normality" is inadequate, and the whole article can be further wikified. Plus I need to double-check all the examples. I'll be revising and tidying later this week, if someone else doesn't. -- FirstPrinciples 14:48, Sep 25, 2004 (UTC)
- Further units to add: molality & formal -- FirstPrinciples 16:02, Sep 25, 2004 (UTC)
- OK I added those too. Still needs tidying up. -- FirstPrinciples 07:29, Sep 26, 2004 (UTC)
Weight-volume percentage
Removed the following from the article until clarified.
- Weight-volume percentage, (sometimes referred to as mass-volume percentage and often abbreviated as w/v) denotes the mass of a substance in a mixture as a percentage of the volume of the entire mixture. For instance: in the previous example 40 grams of ethanol was mixed with 60 grams of water. However, ethanol is less dense than water (with a specific gravity of 0.789), so the total volume of the bottle is 110.7 millilitres; this means that the bottle contains around 36% ethanol, w/v.
- Note: It is usual practise to label alcoholic beverages with weight-volume percentages, although some less scrupulous manufacturers give the proportion of alcohol as weight-for-weight, thereby making drink appear slightly stronger than it is. In many areas this practice is restricted by fair trading laws.
My reasoning
There is a problem here, volumes of alcohol and water do not add. 60g water/1.0g/mL = 60mL. 40g ethanol/0.789g/mL =50.7mL. But 60mL water plus 50.7mL ethanol does not = 110.7mL, but something less than that for a total volume.
This is a common demo in introductory chemistry. Combine 10mL water with 10mL alcohol; the expected combined volume is 20mL. Students are quite surprised to find the combined volume to be measurably less.
So, if alcohol trade laws are based on this concept they are in error.
I have not heard of this weight-volume concentration term and find it troubling even without the above mentioned glitch. It may be an odd term used in the alcohol industry, if so we need to define and explain it better before putting it back in.-Vsmith 22:11, 30 Sep 2004 (UTC)
OK, I recant:-) I have heard of weight-volume. Weight-volume percentage is often used for solutions made from solid reagents. It is the weight of the solute in grams multiplied by one hundred divided by the volume of solution in milliliters. Need to re-write this without the volume mixing problems and re-insert. More to do. -Vsmith 01:44, 1 Oct 2004 (UTC)
ppt?
Parts per thousand (ppt)
Parts per trillion (ppt)
OK we have a problem here ppt cannot mean both per thosand and per trillion. In my experience ppt means parts per trillion.
Parts per thousand is represented by the per mil symbol: (% symbol with an extra zero), don't know what the code is for it. Looks sorta like this o/oo . -Vsmith 22:57, 30 Sep 2004 (UTC)
OK, found it: parts per thousand or 'per mil' ‰.
[1]
-Vsmith 00:58, 1 Oct 2004 (UTC)