Talk:Mass concentration (chemistry)

Units

I think this page is wrong. Every (w/v) calculation I have seen is g/100ml. g/l and kg/m^3 are used for density, but not concentration.— Preceding unsigned comment added by 132.177.115.47 (talk • contribs) 15:34, 30 March 2011

Even though it may not be used very often, kg/m^3 is the correct SI-unit! However, regarding the "commonly used" unit, it is okay for me to change it to whatever you think is most often used. It could be mentioned that g/100mL is the same as g/dL. RolfSander (talk) 15:53, 30 March 2011 (UTC)

In all the biochemistry labs I've worked in, most people say mg/ml (pronounced migs-per-mil or migs-per-em-el) for protein concentration. In the literature it is usually mg/ml or g/l. Fortunately these both turn out to be the same as kg/m^3. For detergents, bulk solution constituents like glycerol, cell culture medium constituents like tryptone, dextrose, and many other things it is usually "%", usually without specifying whether it is by mass, volume, or mass/volume. For example, the first full article in the current "journal of biological chemistry" (http://www.jbc.org/content/290/52/30736.full.pdf) uses mg/ml twice (for fibronectin and "G418") and "%" more than 10 times (Triton, saponin, trichloroacetic acid, paraformaldehyde, fetal bovine serum, CO2, and Bovine Serum Albumin (a protein!)). I believe medical labs often report results as (m)g/dL, for example in the blood test report.Eaberry (talk) 15:59, 31 December 2015 (UTC)

Symbol for mass concentration

I prefer the symbol gamma ($\gamma$) for the mass concentration of one component in a solution because rho ($\rho$) is normally used for density. I think that using rho for both creates confusion. What do others think? RolfSander (talk) 12:08, 1 April 2011 (UTC)

The symbol rho underlines that when the component is pure (mass fraction 1) the density equals mass concentration and mass concentration equals the density. Concerning the risk of confusion the symbol for density of the mixture is rho without subscript _i indicating component i unlike mass concentration of the component which is subscripted.

$\rho =\rho _{i}^{0}$

The mass concentration or density of pure component could be denoted by rho_i0, 0 indicating pure component.--MagnInd (talk) 08:31, 3 April 2011 (UTC)-

If you insist on rho instead of gamma, well, okay, fine with me. However, for consistency, then please also adjust all occurences of gamma on the Concentration page! RolfSander (talk) 21:44, 3 April 2011 (UTC)

User Tadeu changed "mass concentration" variable to C instead of rho, because rho is already used for "mass density". I undid the revision. The options that we have are rho and gamma but not C. However, I agree with Tadeu that it is confusing to use the same symbol as for density.--RolfSander (talk) 07:38, 18 August 2012 (UTC)

I've never seem this use of $\rho ^{0}$ for density of the pure component, it is always only $\rho$ or $\rho _{i}$. Why the options that we have are only $\rho$ and $\gamma$, but not uppercase $C$? I've seem $C$ being used for mass concentration in many domains, it is a straightforward abbreviation, and it does not clash with any other common variable. --Tadeu (talk) 18:56, 24 August 2012 (UTC)

It can be encountered in sources like, for instance, (by) William B Krantz.--MagnInd (talk) 21:59, 25 August 2013 (UTC)

$\rho _{i}^{0}$ or $\rho _{i}^{*}$ refers to case when the mass concentration has the same numerical value to mass density, namely for a pure component. This notation is similar to that encountered in the statement of Raoult's law $P^{0}$ or $P^{*}$.--MagnInd (talk) 21:54, 25 August 2012 (UTC)

It clashes with number concentration which also has the symbol $C$, see IUPAC page: [1]--RolfSander (talk) 20:40, 24 August 2012 (UTC)

In order to avoid confusion and also to underline the significance (the connection between the two quantities mass concentration and mass density), the best solution is to use bolded rho or $\varrho _{i}\,$ (like on nl.wp) for mass concentration while keeping the unmodified rho for mass density. This implies that any other Wikipedia requirements which might be contrary to this purpose be ignored.--MagnInd (talk) 12:38, 23 August 2012 (UTC)

Bold is very bad for distinguishing one variable from another, and it is already used for distinguishing vectors or matrices from scalars. --Tadeu (talk) 18:56, 24 August 2012 (UTC)

I agree that bold should only be used for vectors or matrices. Using rho and varrho is a nice idea but wikipedia should describe common usage and not invent new things.--RolfSander (talk) 20:40, 24 August 2012 (UTC)

There are two kinds of bold allowed by LaTex sintax: one for vectors and one for number sets notation like the set of natural or integer numbers.--MagnInd (talk) 09:28, 24 August 2013 (UTC)

The common usage is fragmented/inconsistent in various sources and doesn't cover all situations regarding relations between quantities expressing composition relating to this issue (mass concentration, mass concentration of a pure component aka mass density of that component, volume fraction and volume concentration like below) altogheter, which situations require a consistent and systematic notation to which varrho suites the best.

So this is a clear case when the greatness of Wikipedia could be seen in action, namely by applying WP:IAR because the requirement of common usage gets in the way of a systematic description or picture, that is against the improvement of Wikipedia articles.--MagnInd (talk) 21:39, 25 August 2012 (UTC)

% is Incorrect?

My university uses %w/v. How can this be incorrect? --Andrew Mackintosh 17:38, 8 April 2011 (UTC)

Think for yourself. The notation %w/v is flawed for two reasons. One: the percent notation applies to quotients of same dimension of a physical quantity and two: this percent can be greater than 100 when the concentration is greater than 100 g/100 ml or 100 mg/100 ml. The essential is that the unit g/dl or g/100 ml is improperly considered as percent. Is the incorrectness clear enough?--MagnInd (talk) 11:24, 9 April 2011 (UTC)

Thanks for the nice explanation, MagnInd! I should add that there are occasions where numbers greater than 100 % are possible, for example in "the prices increased by 200 %". Anyway, you are of course correct that one component of a solution cannot contribute more than 100 % to the total. RolfSander (talk) 13:10, 9 April 2011 (UTC)

Please cite a reasonable source which details why this is incorrect. w/v percentage in biology is a convention; it's purpose is to convey quickly relative concentrations of biochemical solutions. It is good to point out how this differs from a strict chemical definition, but bashing this convention based on how technically and mathematically accurate it is (which is what the current article does) adds nothing to the article. NingOTI (talk) 16:18, 26 February 2018 (UTC)

In my experience the simple designation of "%" is not confined to biology. In industrial chemistry, the term is very common, and is understood to normally mean w/v percentage or w/w percentage, there being very little practical difference between the two in most cases. However, for industrial processing, because it is convenient to weigh a particular quantity into a volume of liquid, the term "%" normally refers to "w/v%" or "%(w/v)".Skelta (talk) 05:21, 29 May 2018 (UTC)

Titer- another page to redir or disambig

Titer page should also be made a disambiguation page or a redirect page to mass concentration (chemistry). It seems that it mixes to aspects: the titer as (mass) concentration and the titer of a fat.--MagnInd (talk) 20:59, 14 May 2011 (UTC)

I moved titer away from the first sentence. I don't think it is important enough to be up there. It is now mentioned in the "Definition" section. Also, I don't think that titer necessarily refers to MASS concentration. I think the titer could also be expressed e.g. as a molar concentration.--RolfSander (talk) 19:25, 4 December 2011 (UTC)

Other related quantities: volume fraction and concentration

Relations to these quantities could be added.--MagnInd (talk) 23:23, 14 December 2011 (UTC)

$\rho _{i}=\rho _{i}^{*}{\frac {V_{i}}{V}}\,=\rho _{i}^{*}{\frac {n_{i}V_{i}^{*}}{V}}\,$

or

${\tilde {\rho _{i}}}=\rho _{i}{\frac {V_{i}}{V}}\,=\rho _{i}{\frac {n_{i}V_{i}^{*}}{V}}\,$--MagnInd (talk) 23:37, 14 December 2011 (UTC)

or

$\varrho _{i}=\rho _{i}{\frac {V_{i}}{V}}\,=\rho _{i}{\frac {n_{i}V_{i}^{*}}{V}}\,$--MagnInd (talk) 08:06, 5 September 2013 (UTC)

Multiplicative inverse

The inverse of this quantity is distinct from both specific volume and partial specific volume as the inverse of molar concentration is distinct from partial molar volume.--MagnInd (talk) 21:59, 21 August 2013 (UTC)

Yes, the inverse is 1/density only when the substance is pure (usually not the case, and certainly not for solutions). For solutions, I don't know what the inverse of mass concentration is called. So I've removed the paragraph. SBHarris 02:04, 22 August 2013 (UTC)

The situation is similar to the inverse of molar concentration, so the name specific dilution or specific dilution volume seems apropriate.--MagnInd (talk) 09:19, 24 August 2013 (UTC)