Synthesized answer
The author suggests that the separation of carbon dioxide from soda-water by heat indicates a compound (carbonic acid), while the separation of sugar from water by evaporation indicates a mere mixture, because the distinction is guided by "analogy" [1]. Specifically, the author states that it is "probable that the compound named carbonic acid is really contained in a solution of carbon dioxide in water, on account of the formulae and behaviour of the carbonates" [1]. This analogy relies on the chemical behavior of carbonates, which are known compounds, to infer that carbon dioxide in water forms a compound rather than a simple mixture.
The chemical principle behind this distinction is that the separation of elements from a compound typically requires chemical treatment, whereas separation of mixture constituents can be done by mechanical or physical means [1]. However, the author acknowledges this line is difficult to draw sharply, as both separations here involve heat—a physical process. The key difference is that carbonic acid (H₂CO₃) is a "very easily decomposable substance" that splits into CO₂ and water when liberated [2], and its existence is supported by the behavior of…
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Again, it is usually accepted that the separation of the constituents of a mixture may be effected by mechanical, or at least by physical means ; whereas the separation of the elements from a compound require chemical treatment. Here it is difficult to draw a sharp distinction. The VOL. II. A 2 MODERN CHEMISTRY separation of carbon dioxide from soda-water by the appli- cation of heat is similar in character to the separation of sugar from water by evaporation of the water ; yet we believe that a solution of carbon dioxide in water consti- tutes a compound, while that of sugar in…
Carbonic acid is a very easily decomposable substance ; if liberated, unless a great deal of water be present, it splits into its anhydride, CO2, and water: O=C(OH)2 = CO2 -f H0O. The anhydride is a colourless gas, which con- denses to a solid at about —80° ; it can be liquefied only under pressure. Carbon dioxide, or carbonic anhydride, is produced by heating a carbonate ; as already remarked, all carbonates, except those of the alkaline metals, are decomposed by heat, forming oxides, and evolving carbon dioxide. It is also produced when carbon or carbon monoxide is burned with…
d a limekiln ; the coal is set on fire, and its heat expels the carbon dioxide from the carbonate : CaCO3 = CaO-fCO.,. If calcium carbonate be heated in a closed vessel, however, so that the carbon dioxide does not escape, the dissociation proceeds until the amount of carbon dioxide in the vessel has reached a certain proportion, which is per- fectly definite for each temperature, or until the carbon dioxide has attained a certain " concentration." The reaction then stops. But if the carbon dioxide be removed as it is formed, the reaction goes on to the end, until all carbon
thus: KOH.Aq + HBr.Aq=KBr.Aq + H2O. It will be noticed that the water is not ionised, nor does it hydro- lyse the potassium bromide ; hence, on evaporation, as concentration increases, the number of ions of potassium and bromine becomes fewer and fewer, and after the water has been removed the pure dry salt is left. With a carbonate the action is similar. The equation is Li2CO3.Aq + zHI.Aq = 2LiL Aq + H2O + CO2. In dilute solution the acid H2CO3 would be liberated ; it is a very weak acid, i.e. it is comparatively very slightly ionised into + aH.Aq and CO3.Aq ; and, moreover, it…
called carbonic acid), and of carbon disulphide. Carbon is a tetrad, and the analogue of carbon tetrachloride would be the tetrahydroxide, C(OH)4; but this body is unstable, and its first anhydride, O=C(OH)2, is known only in aqueous solution. However, carbonyl chloride, O=CC10, exists ; it is produced by the direct union of carbonic oxide with chlorine, when a mixture of both gases is exposed to sunlight ; it was formerly known as " phosgene gas," meaning "made by light"; but it is more conveniently prepared by passing a mixture of the two gases over animal charcoal heated to…
More questions about this book
- How did the historical lack of distinction between mixtures and compounds, and John Dalton's subsequent formulation of laws, fundamentally alter the scientific approach to classifying chemical substances?
- The text states that "a mixture may be homogeneous; a compound must." Explain why homogeneity alone is not a sufficient criterion to definitively classify a substance as a compound, using examples from the text.
- Using the provided evidence for the atmosphere, explain why it is classified as a mixture rather than a compound, focusing on the properties of its gaseous constituents and how this simplifies the classification problem compared to other types of substances.
- Based on the challenges and nuances presented in the text, what are the two most crucial criteria you would use to distinguish between a mixture and a compound, and what are the primary difficulties or exceptions you would highlight when applying these criteria?