![]() | This ![]() It is of interest to the following WikiProjects: | ||||||||||
|
I don't understand this new equation which supposedly describes the relation between molality and the mass of the solvent:
The sum describes the mass of all solutes, and is probably the mass of the solvent. Then on the left hand side is the mass of the solution. There is no molality in the equation. RolfSander ( talk) 21:47, 14 April 2011 (UTC)
Mi molar mass of the component -- MagnInd ( talk) 23:00, 14 April 2011 (UTC)
The equation derived is useful especially for binary solutions where the molality of the solute can be expressed from the mass fraction of the solvent.
The conversion to and from molar concentration(s) will be derived.-- MagnInd ( talk) 12:52, 15 April 2011 (UTC)
It seems that starting with ternary solutions, there isn't an explicit algebraic relation between the molality and the mass fraction of a solute.-- MagnInd ( talk) 10:01, 17 July 2011 (UTC)
Extended content
|
---|
From the following mass balance a relation between molality and the mass of the solvent can be derived by dividing the equality by the mass of the solvent.
gives or equivalent to where ws is the mass fraction of the solvent and nj the amounts of solutes. Substuting w_i from
gives the searched relation for binary mixtures For n-ary mixtures the conversion is: where the denominator represents the reciprocal of the mass fraction of the solvent. n-ary mixtures the denominator represents the mass concentration of the solvent substituted in the rearranged definition |
This article is terrible - the definitions almost appear intentionally vague. — Preceding unsigned comment added by 67.238.101.3 ( talk) 00:32, 27 July 2011 (UTC)
It would be interesting to add some details about who defined the concept and gave the name molality.-- MagnInd ( talk) 21:58, 28 August 2011 (UTC)
Thanks, Toolnut, for all your edits here. I support your change from m to b as the symbol for molality because it avoids the confusion with m for mass. However, I would like to see a general consensus here for the change. Do others agree as well?
If we now keep the symbol b, we will also have to check and if necessary adjust all pages that may refer to molality, e.g.: Molar concentration · Mass concentration · Number concentration · Volume concentration · Normality · Percentage solution · Mole fraction · Mass fraction · Mixing ratio RolfSander ( talk) 21:27, 11 November 2011 (UTC)
Thanks again, Toolnut, for completing the derivation of relations to other compositional quantities.-- MagnInd ( talk) 12:34, 20 November 2011 (UTC)
Since we seem to have a consensus here to use the symbol b for molality, I have now adjusted the pages Molar concentration and Mass concentration.-- RolfSander ( talk) 23:04, 2 December 2011 (UTC)
The density of solvent , if appears in the conversion formulae, should have the symbol to avoid confusion with the mass concentration of solvent having the subscript zero.-- MagnInd ( talk) 20:53, 29 November 2011 (UTC)
sum symbol forgotten-- MagnInd ( talk) 23:19, 14 December 2011 (UTC)
(relation to volume concentration)
The distinction is done by the star superscript.-- MagnInd ( talk) 20:12, 9 December 2011 (UTC)
A solution to this dilemma could be the the assigning the symbol rho with say tilde above to mass concentration and leaving rho unsuperscripted to densities of components. This minimize the potential for confusion while keeping the intrinsic connection between the two.-- MagnInd ( talk) 10:23, 15 December 2011 (UTC)
The density of the solvent appears in the relation between molality and apparent molar property.-- 5.15.57.134 ( talk) 09:21, 4 September 2014 (UTC)
A mixed ratio is dimensional, unlike ratio of quantities with the same dimension such as mass, amount.-- MagnInd ( talk) 20:37, 6 December 2011 (UTC)
It seems that mass ratio or amount ratio are not covered on en.wp unlike in de.wp: [1]-- MagnInd ( talk) 20:44, 6 December 2011 (UTC)
As an industrial chemist for 35 years I virtually never encounter this in the literature. The only place I've seen this is in textbooks. I am wondering whether it is actually used, and if so where? Perhaps pharmaceutical chemistry? Some examples from the literature (NOT textbooks) would be appropriate. The concept is a lot more of a problem than is claimed here. A solution of NaCl, for instance, will solvate certain compounds that water alone will not. What is the solvent in the cases where while there may be only one liquid, but the solvent is a mixture? What if two solids when combined form a liquid mixture? In industrial chemistry it is VERY common that the appropriate combination of two (occasionally three) solvents makes a better solvent than any of the components. I *HIGHLY* question the (not clearly articulated) assertion made here that only one (liquid) chemical can be "the" solvent. Actually, this concept breaks down as you move away from ideal binary solute-solvent systems. Given any system {A,B} with interactions A-A, B-B, and A-B, the solvency can be defined as the A-B interactions. As soon as you move to a trinary system {A,B,C} determination of whether A-B, A-C, and B-C interactions are "solvent-like" (compared to some vague alternative) borders on the absurd. Seems to me that molality is more a subject of mixology than chemical science. That is, it aids the technician making up solutions, rather than having any intrinsic theoretical value. Another example of the problem how does molality fair when water is replaced with heavy water? Suddenly "b" changes by 20% ?? Is there ANY area of study that it is regularly used? Other than to waste the student's time in learning esoterica? If so, cite it, if not I suggest the article state that it has not been widely accepted and because of its limited applicability (unless it can be defined for multicomponent solutions) its use is usually depreciated.Define it or state that there is no clear definition for other than binary mixtures. 71.31.149.224 ( talk) 20:30, 1 July 2012 (UTC)
Unless I'm mistaken, it seems the conversion of molality to mass fraction as of december 1, 2014 is missing a factor of 1000 in :
due to assuming 1kg of solvent while using grams for the molar mass etc. Why is the equation not
If this is not the case, then it's confusing as to what units are used.-- 169.234.32.227 ( talk) 23:54, 30 November 2014 (UTC)
I see from the history of this article a recent edit involving the 1000 factor and its presence when some units are used. Perhaps this factor of 1000 can appear in the general formula but in paranthesis like (1000). Thoughts?-- 185.53.197.247 ( talk) 11:34, 16 April 2019 (UTC)
Please do not use a factor of 1000 in these formulas! If you use SI units, the factor is not necessary. If you use non-SI units, there are a zillion of possible units you could insert into any formula, depending whatever units you prefer. -- RolfSander ( talk) 12:01, 16 April 2019 (UTC)
The advantage mentioned is an advantage, but not at all extent. Even mass changes; which is given by ; m is rest mass. Should this to be mentioned in appropriate language, even though it doesn't affect much, and not a big difference is possible in everyday life.
aGastya
✉ Dicere Aliquid :)
02:01, 7 May 2015 (UTC)
I notice that there are some objections to the term molality fraction, recently inserted in article and used in some sources to calculate an apparent molar mass for a pseudocomponent from a ternary solution considered pseudo-binary mixture in order to define an apparent molar property for a (pseudo)component as volume just like for the case of usual binary mixtures.-- 82.137.9.23 ( talk) 20:03, 19 October 2017 (UTC)
I put here the removed formula:
which can be similar to the name ionic strength fraction encountered in other sources.-- 82.137.9.23 ( talk) 20:11, 19 October 2017 (UTC)
Therefore, when ionic strength is expressed as molality, the name molality fraction is nearby as an immediate consequence.-- 82.137.9.23 ( talk) 20:23, 19 October 2017 (UTC)
The name molality fraction has been removed on the ground of insufficient reference for it. What would be the sufficient number of references?-- 82.137.9.166 ( talk) 20:51, 23 October 2017 (UTC)
I've checked another source in another journal ( Food Science) which uses the same formula for an mean apparent molar mass of the 2 solutes and the same ratios of molalities but this time just not naming in any way the two ratios involving molalities. The ratios of molalities leads to a complex fraction which finally simplifies and gives a ratio of molar amounts.
Is this a better solution not to name the two ratios?-- 82.137.9.114 ( talk) 09:04, 24 October 2017 (UTC)
In general, topics worth mentioning are described here: [4]. For the case of "molality fraction", I think it would be notable if it is used in more than just one or a few specific articles. However, it is neither mentioned in the IUPAC gold book [5] nor in any chemistry text book, AFAIK. I think the reason why the term "molality fraction" is hardly used is because it is not really related to molality. The mass of the solvent cancels out. You could just as well define a "molarity fraction" (note the letter "r" here) and get the same value because the volume of the solution cancels out here as well. Both would be identical to a simple mole fraction. -- RolfSander ( talk) 09:11, 24 October 2017 (UTC)
Some aspects concerning this mentioned relation will be introduced in article.-- 82.137.13.190 ( talk) 14:14, 25 October 2017 (UTC)
The following block of text will be introduced which underlies the mentioned relation:-- 82.137.13.190 ( talk) 14:24, 25 October 2017 (UTC)
For concentrated ionic solutions the activity coefficient of the electrolyte is split into electric and statistical components.
The statistical part includes hydration index number h , the number of ions from the dissociation and the ratio r between the apparent molar volume of the electrolyte and the molar volume of water and molality b of the electrolyte.
Concentrated solution statistical part of the activity coefficient is:
[1],
[2]
[3]
I think the relation to apparent molar volume would need further details about intermediate steps in derivation.-- 5.2.200.163 ( talk) 13:41, 3 August 2018 (UTC)
See the talk:Apparent molar property#Relation to molality for comparison of equations.-- 5.2.200.163 ( talk) 14:23, 3 August 2018 (UTC)
I think that this article needs a section with multiples and submultiples for the main molality unit, in connection to the factor of 1000, mentioned above. Amy suggestions?-- 109.166.129.142 ( talk) 00:29, 20 July 2019 (UTC)
By IUPAC definition a concentration is defined exclusively with respect to volume. Accordingly, "molal concentration" is not even listed among the possibilities and the definition of molality does not use the term "concentration". -- Geon79 ( talk) 23:37, 23 September 2019 (UTC)
The above discused factor of 1000 enters the unit for molar mass when not present explicitly.-- 178.138.99.40 ( talk) 18:59, 24 May 2021 (UTC)
![]() | This ![]() It is of interest to the following WikiProjects: | ||||||||||
|
I don't understand this new equation which supposedly describes the relation between molality and the mass of the solvent:
The sum describes the mass of all solutes, and is probably the mass of the solvent. Then on the left hand side is the mass of the solution. There is no molality in the equation. RolfSander ( talk) 21:47, 14 April 2011 (UTC)
Mi molar mass of the component -- MagnInd ( talk) 23:00, 14 April 2011 (UTC)
The equation derived is useful especially for binary solutions where the molality of the solute can be expressed from the mass fraction of the solvent.
The conversion to and from molar concentration(s) will be derived.-- MagnInd ( talk) 12:52, 15 April 2011 (UTC)
It seems that starting with ternary solutions, there isn't an explicit algebraic relation between the molality and the mass fraction of a solute.-- MagnInd ( talk) 10:01, 17 July 2011 (UTC)
Extended content
|
---|
From the following mass balance a relation between molality and the mass of the solvent can be derived by dividing the equality by the mass of the solvent.
gives or equivalent to where ws is the mass fraction of the solvent and nj the amounts of solutes. Substuting w_i from
gives the searched relation for binary mixtures For n-ary mixtures the conversion is: where the denominator represents the reciprocal of the mass fraction of the solvent. n-ary mixtures the denominator represents the mass concentration of the solvent substituted in the rearranged definition |
This article is terrible - the definitions almost appear intentionally vague. — Preceding unsigned comment added by 67.238.101.3 ( talk) 00:32, 27 July 2011 (UTC)
It would be interesting to add some details about who defined the concept and gave the name molality.-- MagnInd ( talk) 21:58, 28 August 2011 (UTC)
Thanks, Toolnut, for all your edits here. I support your change from m to b as the symbol for molality because it avoids the confusion with m for mass. However, I would like to see a general consensus here for the change. Do others agree as well?
If we now keep the symbol b, we will also have to check and if necessary adjust all pages that may refer to molality, e.g.: Molar concentration · Mass concentration · Number concentration · Volume concentration · Normality · Percentage solution · Mole fraction · Mass fraction · Mixing ratio RolfSander ( talk) 21:27, 11 November 2011 (UTC)
Thanks again, Toolnut, for completing the derivation of relations to other compositional quantities.-- MagnInd ( talk) 12:34, 20 November 2011 (UTC)
Since we seem to have a consensus here to use the symbol b for molality, I have now adjusted the pages Molar concentration and Mass concentration.-- RolfSander ( talk) 23:04, 2 December 2011 (UTC)
The density of solvent , if appears in the conversion formulae, should have the symbol to avoid confusion with the mass concentration of solvent having the subscript zero.-- MagnInd ( talk) 20:53, 29 November 2011 (UTC)
sum symbol forgotten-- MagnInd ( talk) 23:19, 14 December 2011 (UTC)
(relation to volume concentration)
The distinction is done by the star superscript.-- MagnInd ( talk) 20:12, 9 December 2011 (UTC)
A solution to this dilemma could be the the assigning the symbol rho with say tilde above to mass concentration and leaving rho unsuperscripted to densities of components. This minimize the potential for confusion while keeping the intrinsic connection between the two.-- MagnInd ( talk) 10:23, 15 December 2011 (UTC)
The density of the solvent appears in the relation between molality and apparent molar property.-- 5.15.57.134 ( talk) 09:21, 4 September 2014 (UTC)
A mixed ratio is dimensional, unlike ratio of quantities with the same dimension such as mass, amount.-- MagnInd ( talk) 20:37, 6 December 2011 (UTC)
It seems that mass ratio or amount ratio are not covered on en.wp unlike in de.wp: [1]-- MagnInd ( talk) 20:44, 6 December 2011 (UTC)
As an industrial chemist for 35 years I virtually never encounter this in the literature. The only place I've seen this is in textbooks. I am wondering whether it is actually used, and if so where? Perhaps pharmaceutical chemistry? Some examples from the literature (NOT textbooks) would be appropriate. The concept is a lot more of a problem than is claimed here. A solution of NaCl, for instance, will solvate certain compounds that water alone will not. What is the solvent in the cases where while there may be only one liquid, but the solvent is a mixture? What if two solids when combined form a liquid mixture? In industrial chemistry it is VERY common that the appropriate combination of two (occasionally three) solvents makes a better solvent than any of the components. I *HIGHLY* question the (not clearly articulated) assertion made here that only one (liquid) chemical can be "the" solvent. Actually, this concept breaks down as you move away from ideal binary solute-solvent systems. Given any system {A,B} with interactions A-A, B-B, and A-B, the solvency can be defined as the A-B interactions. As soon as you move to a trinary system {A,B,C} determination of whether A-B, A-C, and B-C interactions are "solvent-like" (compared to some vague alternative) borders on the absurd. Seems to me that molality is more a subject of mixology than chemical science. That is, it aids the technician making up solutions, rather than having any intrinsic theoretical value. Another example of the problem how does molality fair when water is replaced with heavy water? Suddenly "b" changes by 20% ?? Is there ANY area of study that it is regularly used? Other than to waste the student's time in learning esoterica? If so, cite it, if not I suggest the article state that it has not been widely accepted and because of its limited applicability (unless it can be defined for multicomponent solutions) its use is usually depreciated.Define it or state that there is no clear definition for other than binary mixtures. 71.31.149.224 ( talk) 20:30, 1 July 2012 (UTC)
Unless I'm mistaken, it seems the conversion of molality to mass fraction as of december 1, 2014 is missing a factor of 1000 in :
due to assuming 1kg of solvent while using grams for the molar mass etc. Why is the equation not
If this is not the case, then it's confusing as to what units are used.-- 169.234.32.227 ( talk) 23:54, 30 November 2014 (UTC)
I see from the history of this article a recent edit involving the 1000 factor and its presence when some units are used. Perhaps this factor of 1000 can appear in the general formula but in paranthesis like (1000). Thoughts?-- 185.53.197.247 ( talk) 11:34, 16 April 2019 (UTC)
Please do not use a factor of 1000 in these formulas! If you use SI units, the factor is not necessary. If you use non-SI units, there are a zillion of possible units you could insert into any formula, depending whatever units you prefer. -- RolfSander ( talk) 12:01, 16 April 2019 (UTC)
The advantage mentioned is an advantage, but not at all extent. Even mass changes; which is given by ; m is rest mass. Should this to be mentioned in appropriate language, even though it doesn't affect much, and not a big difference is possible in everyday life.
aGastya
✉ Dicere Aliquid :)
02:01, 7 May 2015 (UTC)
I notice that there are some objections to the term molality fraction, recently inserted in article and used in some sources to calculate an apparent molar mass for a pseudocomponent from a ternary solution considered pseudo-binary mixture in order to define an apparent molar property for a (pseudo)component as volume just like for the case of usual binary mixtures.-- 82.137.9.23 ( talk) 20:03, 19 October 2017 (UTC)
I put here the removed formula:
which can be similar to the name ionic strength fraction encountered in other sources.-- 82.137.9.23 ( talk) 20:11, 19 October 2017 (UTC)
Therefore, when ionic strength is expressed as molality, the name molality fraction is nearby as an immediate consequence.-- 82.137.9.23 ( talk) 20:23, 19 October 2017 (UTC)
The name molality fraction has been removed on the ground of insufficient reference for it. What would be the sufficient number of references?-- 82.137.9.166 ( talk) 20:51, 23 October 2017 (UTC)
I've checked another source in another journal ( Food Science) which uses the same formula for an mean apparent molar mass of the 2 solutes and the same ratios of molalities but this time just not naming in any way the two ratios involving molalities. The ratios of molalities leads to a complex fraction which finally simplifies and gives a ratio of molar amounts.
Is this a better solution not to name the two ratios?-- 82.137.9.114 ( talk) 09:04, 24 October 2017 (UTC)
In general, topics worth mentioning are described here: [4]. For the case of "molality fraction", I think it would be notable if it is used in more than just one or a few specific articles. However, it is neither mentioned in the IUPAC gold book [5] nor in any chemistry text book, AFAIK. I think the reason why the term "molality fraction" is hardly used is because it is not really related to molality. The mass of the solvent cancels out. You could just as well define a "molarity fraction" (note the letter "r" here) and get the same value because the volume of the solution cancels out here as well. Both would be identical to a simple mole fraction. -- RolfSander ( talk) 09:11, 24 October 2017 (UTC)
Some aspects concerning this mentioned relation will be introduced in article.-- 82.137.13.190 ( talk) 14:14, 25 October 2017 (UTC)
The following block of text will be introduced which underlies the mentioned relation:-- 82.137.13.190 ( talk) 14:24, 25 October 2017 (UTC)
For concentrated ionic solutions the activity coefficient of the electrolyte is split into electric and statistical components.
The statistical part includes hydration index number h , the number of ions from the dissociation and the ratio r between the apparent molar volume of the electrolyte and the molar volume of water and molality b of the electrolyte.
Concentrated solution statistical part of the activity coefficient is:
[1],
[2]
[3]
I think the relation to apparent molar volume would need further details about intermediate steps in derivation.-- 5.2.200.163 ( talk) 13:41, 3 August 2018 (UTC)
See the talk:Apparent molar property#Relation to molality for comparison of equations.-- 5.2.200.163 ( talk) 14:23, 3 August 2018 (UTC)
I think that this article needs a section with multiples and submultiples for the main molality unit, in connection to the factor of 1000, mentioned above. Amy suggestions?-- 109.166.129.142 ( talk) 00:29, 20 July 2019 (UTC)
By IUPAC definition a concentration is defined exclusively with respect to volume. Accordingly, "molal concentration" is not even listed among the possibilities and the definition of molality does not use the term "concentration". -- Geon79 ( talk) 23:37, 23 September 2019 (UTC)
The above discused factor of 1000 enters the unit for molar mass when not present explicitly.-- 178.138.99.40 ( talk) 18:59, 24 May 2021 (UTC)