Re: Roy et al.: Densities and Viscosities of Citric Acid in Aqueous Cetrimonium Bromide Solutions with Reference to the Manifestation of Solvation.(4) In the article cited above, the limiting (standard) molar volumes for citric acid in water, at various temperatures, are given in Table 2 as 203.55; 213.29; and 223.41 cm³ mol^–1 at 25, 35, and 45 °C, respectively, and in aqueous solutions of cetrimonium bromide (CB) as follows: in 0.001 M CB, 230.91, 236.46, and 242.32 cm³ mol^–1; in 0.003 M CB, 233.36, 243.04, and 253.20 cm³ mol^–1; and in 0.005 M CB, 238.95, 247.97, and 257.39 cm³ mol^–1 at 25, 35, and 45 °C, respectively. Given that the molecular weight of citric acid is 192.12 g mol^–1 (210.14 g mol^–1 for the monohydrate) and that the specific volume of analogous compounds tends to be around 0.6–0.7 cm³ g^–1, the standard molar volumes reported by Roy et al. are certainly high. To illustrate the point, here are some values reported in the literature for citric acid in pure water (this is by no means an exhaustive list): 112.44 cm³ mol^–1 at 25 °C (ref (1)); 115.2, 116.7, and 118.9 cm³ mol^–1 at 25, 35 and 45 °C, respectively (ref (2)); 115.20 cm³ mol^–1 at 20 °C (ref (3)). The values reported in refs (2and3) are not strictly standard molar volumes. They are, rather,the results obtained at the lowest concentration reported (0.03 m) (ref (2)) and at 20 °C and m = 0.161 (ref (3)), in that order. These minor variations are not enough to account for the differences observed between the volumes reported by Roy et al. and references (1−3). Additional evidence which shows that the temperature dependence of the standard molar volumes is also in error, can be provided. In going from 25 to 45 °C, the standard values for citric acid (in pure water) reported by Roy et al. increase by about 20 cm³ mol^–1 (∼203–223) which is a change of about 1.0 cm³ mol^–1 K^–1. That expansion is much higher than anything previously reported. The values in ref (2) increase by 3.7 cm³ mol^–1 over the same temperature range, which leads to an expansion, assuming linearity, of about 0.18 cm³ mol^–1 K^–1, a number consistent with results reported for similar compounds. The expansion reported by Roy et al. is about five times higher. The fact that Roy et al. worked with the monohydrate will change the numbers a bit but not enough to account for the observed differences. The author declares no competing financial interest. This article references 4 other publications.

中文翻译：

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对发表在《化学杂志》上的柠檬酸标准摩尔容量的评论。。数据，2011，56，3285-3290

Re：Roy et al .:溴化十六烷基三溴甲烷水溶液中柠檬酸的密度和粘度（参考溶剂化方法）。（4）在以上引用的文章中，各种条件下水中柠檬酸的极限（标准）摩尔体积温度在表2中给出为203.55; 213.29; 和223.41厘米³摩尔^-1，在25，35和45℃下，分别和在西曲溴铵（CB）如下的水溶液：在0.001M的CB，230.91，236.46，和242.32厘米³摩尔^-1 ; 在0.003 M CB，233.36、243.04和253.20 cm ³ mol ^–1中；并且在0.005 M CB，238.95、247.97和257.39 cm ³ mol ^–1中分别在25、35和45°C下进行。假设柠檬酸的分子量为192.12 g mol ^–1（一水合物为210.14 g mol ^–1），并且类似化合物的比容往往在0.6–0.7 cm ³ g ^–1左右，因此报告的标准摩尔量为由Roy等人撰写。肯定很高。为了说明这一点，以下是文献中报道的纯水中柠檬酸的一些值（绝不是详尽的清单）：在25°C下为112.44 cm ³ mol ^–1（参考文献（1））；在25、35和45°C下分别为115.2、116.7和118.9 cm ³ mol ^–1（参考文献（2））；115.20 cm ³摩尔^–1在20°C（参考（3））。参考文献（2和3）中报道的值并非严格为标准摩尔体积。相反，它们是在最低浓度（0.03 m）（参考文献（2））和20°C且m = 0.161（参考文献（3））下获得的结果。这些微小的变化不足以解决Roy等人报道的体积之间的差异。和参考文献（1-3）。可以提供其他证据，表明标准摩尔体积的温度依赖性也是错误的。在25至45°C的温度下，Roy等人报道的柠檬酸标准值（在纯水中）。增加约20 cm ³ mol ^–1（〜203–223），大约是1.0 cm ³ mol ^–1 K ^–1。这种扩张远高于先前报道的任何扩张。ref（2）中的值在相同温度范围内增加3.7 cm ³ mol ^–1，假定线性度，结果将导致约0.18 cm ³ mol ^–1 K ^–1的膨胀，该数字与类似结果的报道一致化合物。罗伊等人报道的扩展。大约高五倍。罗伊等人的事实。一水合物的作用会稍微改变数字，但不足以解决观察到的差异。作者声明没有竞争性的经济利益。本文引用了其他4个出版物。