Water oxidation numbers

As we have just seen the reaction of alkanes with oxygen to give carbon dioxide and water IS called combustion A more fundamental classification of reaction types places it m the oxidation—reduction category To understand why let s review some principles of oxidation-reduction beginning with the oxidation number (also known as oxidation state)... 

Hydride A compound of hydrogen, specifically one containing H ions, 503 oxidation number, 88 water reaction, 371... 

Here the change in oxidation number per atom of iron is from +2 to +3, or by 1 unit of oxidation, hence the equivalent of iron(II) sulphate is 1 mole. Another important reaction is the oxidation of oxalic acid to carbon dioxide and water ... 

Ionic compounds are named by starting with the name of the cation (with its oxidation number if more than one charge is possible), followed by the name of the anion hydrates are named by adding the word hydrate, preceded by a Greek prefix indicating the number of water molecules in the formula unit. 

Write a balanced chemical equation for (a) the hydrogenation of ethyne (acetylene, C2H2) to ethene (C2H4) by hydrogen (give the oxidation number of the carbon atoms in the reactant and product) (b) the shift reaction (sometimes called the water gas shift reaction, WGSR) (c) the reaction of barium hydride with water. 

A typical reaction of the nonmetal halides is their reaction with water to give oxoacids, without a change in oxidation number ... 

The important compounds of nitrogen with hydrogen are ammonia, Irydrazine, and hydrazoic acid, the parent of the shock-sensitive azides. Phosphine forms neutral solutions in water reaction of phosphorous halides with water produces oxoacids without change in oxidation number. 

Nitrogen dioxide, N02 (oxidation number -t-4), is a choking, poisonous, brown gas that contributes to the color and odor of smog. The molecule has an odd number of electrons, and in the gas phase it exists in equilibrium with its colorless dimer N204. Only the dimer exists in the solid, and so the brown gas condenses to a colorless solid. When it dissolves in water, NOz disproportionates into nitric acid (oxidation number +5) and nitrogen oxide (oxidation number +2) ... 

The blue gas dinitrogen trioxide, N203 (Fig. 15.6, 1), in which the oxidation number of nitrogen is +3, is the anhydride of nitrous acid, HN02, and forms that acid when it dissolves in water ... 

Step 3 Disproportionation in water nitrogen s oxidation number changes from +4 to +5 and +2 ... 

The acid strengths and oxidizing abilities of the halogen oxoacids increase with the oxidation number of the halogen. The hypohalous acids, HXO (halogen oxidation number +1), are prepared by direct reaction of the halogen with water. For example, chlorine gas disproportionates in water to produce hypochlorous acid and hydrochloric acid ... 

Like all the coinage metals, copper forms compounds with oxidation number + 1. However, in water, copper(I) salts disproportionate into metallic copper and copper(II) ions. The latter exist as pale blue [Cu(H20)6]2+ ions in water. 

Silver(I) does not disproportionate in aqueous solution and, in almost all its compounds, silver has oxidation number +1. Apart from silver nitrate, AgN03, and silver fluoride, silver salts are generally only sparingly soluble in water. Silver nitrate is the most important compound of silver and the starting point for the manufacture of silver halides for use in photography. 

The chromium atom in Cr04 has an oxidation number of +6, so it must gain three electrons to be converted into Again, water or hydronium ions must supply hydrogen atoms that combine with the... 

Cl, the oxidizing agent, is reduced to Cl. The oxidation number goes from 0 to - 1. Fe2 the reducing agent, is oxidized. Its oxidation number goes from +2 to +3. Just as the water must go somewhere in part ( ), the electrons must go somewhere in part (6). 

When an acid anhydride reacts with water, the corresponding acid is formed. There is no change in oxidation number of the elements. 

The analysis of soil for organic matter4 is straightforward, involving oxidizing it to carbon dioxide and water. Oxidation can be accomplished in a number... 

The metallic properties increase down any column and towards the left in any row on the periodic table. One important metallic property is that metal oxides are base anhydrides. A base anhydride will produce a base in water. These are not oxidation-reduction reactions. Many metal oxides are too insoluble for them to produce any significant amount of base. However, most metal oxides, even those that are not soluble in water, will behave as bases to acids. A few metal oxides, and their hydroxides, are amphoteric. Amphoteric means they may behave either as a base or as an acid. Amphoterism is important for aluminum, beryllium, and zinc. Complications occur whenever the oxidation number of the metal exceeds +4 as in the oxides that tend to be acidic. 

Chemically, nonmetals are usually the opposite of metals. The nonmetallic nature will increase towards the top of any column and toward the right in any row on the periodic table. Most nonmetal oxides are acid anhydrides. When added to water, they will form acids. A few nonmetals oxides, most notably CO and NO, do not react. Nonmetal oxides that do not react are neutral oxides. The reaction of a nonmetal oxide with water is not an oxidation-reduction reaction. The acid that forms will have the nonmetal in the same oxidation state as in the reacting oxide. The main exception to this is N02, which undergoes an oxidation-reduction (disproportionation) reaction to produce HN03 and NO. When a nonmetal can form more than one oxide, the higher the oxidation number of the nonmetal, the stronger the acid it forms. 

You have seen examples of how Lewis structures can be used to assign oxidation numbers for polar molecules such as water, non-polar molecules such as chlorine, and polar polyatomic ions such as the cyanide ion. 

You can also monitor changes in oxidation numbers in reactions that involve covalent molecules. For example, oxidation number changes occur in the reaction of hydrogen and oxygen to form water. 

Q O The combustion of ammonia in oxygen to form nitrogen dioxide and water vapour involves covalent molecules in the gas phase. The oxidation number method for balancing the equation was shown in an example in this section. Devise a half-reaction method for balancing the equation. Describe the assumptions you made in order to balance the equation. Also, describe why these assumptions did not affect the final result. 

Does the fact that you can assign oxidation numbers of +1 to hydrogen and -2 to oxygen in water mean that water is an ionic substance Explain. 

The oxides of low-valency metals (i.e., with cations in oxidation number < -i-4) are typically ionic compounds [76]. They are most frequently easily obtained in crystalline forms. In ionic metal oxides the coordination of the cations (four to eight) is generally higher than their valency (one to four) and this also occurs for the coordination of 0 oxide ions (three to six). The bulk basic nature of the ionic metal oxides is associated with the strong polarization of the metal-oxygen bond, to its tendency to be dissociated by water and to the basic nature of the products of their reaction with water (i.e., the metal hydroxides) [67]. 

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