Compound formula definition

It has been assumed that the cineol and phosphoric acid enter into combination in molecular proportions, forming a solid compound of definite composition. Helbing and Passmore have described a method in which the compound is weighed, and assume that the percentage of cineol in the phosphoric compound is 61 1 per cent, based on the formula CjQHjgO. H3PO4. 

The chief aim of this formula index, like that of other formula indexes, is to help in locating specific compounds, or even groups of compounds, that might not be easily found in the Subject Index, or in the case of compounds in tables or of many complex coordination compounds, not to be found at all in the Subject Index. AU specific compounds with definite formulas (or even a few less definite) are entered in this index, whether entered specifically in the Subject Index or not. As in the latter index, boldface type is used for formulas of compounds whose preparations are described in detail, in at least one of the references cited. 

The question now arises, how may we determine which one of the various formulas, in the case of the five hexanes for instance, is to be assigned to each individual compound of definite physical properties To which one of the butanes, pentanes and hexanes do we assign the straight chain formula or the name normal In the case of the butanes the answer and the reason for it are found in a new synthesis of one of the butanes. We have given one synthesis of the two butanes, viz., from propyl iodide and methyl iodide. As one propyl iodide yields one butane and the other yields the isomeric butane, we know that one of the two isomeric butanes must have the straight chain or normal formula. But we do not know whether the propyl iodide from which the butane boiling at + i is prepared, is really the one possessing the normal or the iso formula. Therefore, it will be seen that the relationship between the isomeric propyl iodides and the isomeric bu-... 

A complete specification of the structure of a glass is impossible, but for a crystal it is only necessary to give the details of one unit cell. Substances are said to have the same structure if the arrangement of atoms within a unit cell is essentially similar, although the interatomic distances and the dimensions of the cell are different. Structure types are named after a particular example, frequently naturally occurring minerals thus we talk of the rocksalt structure of NaCl or the rutile structure of Ti02. Specifying a definite mineral rather than the compound formula is important, as... 

Reference has already been made to the high melting point, boiling point and strength of transition metals, and this has been attributed to high valency electron-atom ratios. Transition metals quite readily form alloys with each other, and with non-transition metals in some of these alloys, definite intermetallic compounds appear (for example CuZn, CoZn3, Cu3,Sng, Ag5Al3) and in these the formulae correspond to certain definite electron-atom ratios. 

Bismuth trioxide may be prepared by the following methods (/) the oxidation of bismuth metal by oxygen at temperatures between 750 and 800°C (2) the thermal decomposition of compounds such as the basic carbonate, the carbonate, or the nitrate (700—800°C) (J) precipitation of hydrated bismuth trioxide upon addition of an alkah metal hydroxide to a solution of a bismuth salt and removal of the water by ignition. The gelatinous precipitate initially formed becomes crystalline on standing it has been represented by the formula Bi(OH)2 and called bismuth hydroxide [10361 -43-0]. However, no definite compound has been isolated. 

The compounds formed when a hydroxyl group (-OH) is substituted for a hydrogen are called alcohols. They have the general formula R-OH. The hydroxyl radical looks exactly like the hydroxide ion, but it is not an ion. Where the hydroxide ion fits the definition of a complex ion - a chemical combination of two or more atoms that have colleetively lost or (as in this case) gained one or more electrons - the... 

The equivalent weight of an ion (or an element) is the ratio of its formula weight to its valence. According to an alternative definition that is also suitable for compounds, an equivalent weight represents the amount of a substance which will react with one atomic weight of hydrogen or its chemical equivalent. 

Chromic hydroxide, Cr(OH)3, is a compound with low solubility in water. It is usually hydrated and does not have the definite composition represented by the formula. It is quite soluble either in strong acid or strong base. 

Ans. Choice (a). This is a useful definition of empirical formula. The molecular formula gives the ratio of moles of each element to moles of the compound, plus the information given by the empirical formula. The percent composition does not deal with moles, but is a ratio of masses. 

Urea and thiourea have formulas NH2CONH2 and NH2CSNH2. ( ) Explain why they arc considered to be organic compounds. (b) Explain why they do not fit the general definition given in Sec. 21.1. 

Hydrogen is capable of forming compounds with all elements except the noble gases. In compounds with nonmetals, hydrogen usually behaves like a metal instead of a nonmetal. Therefore, when hydrogen combines with a nonmetal, it usually has a +1 oxidation number. When hydrogen combines with a metal, it usually has a —1 oxidation number. Hydrogen compounds with the transition metals are usually nonstoichiometric. Nonstoichiometric compounds have no definite formula. 

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