#### What is the acid base behavior of element oxides? Information and examples about acid base behavior of some common oxides

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Acid Base Behavior Of Element Oxides; Metals are also distinguished from nonmetals by the acid-base behavior of their oxides in water:

• Most main-group metals transfer electrons to oxygen, so their oxides are ionic. In water, these oxides act as bases, producing OH ions and reacting with acids. Calcium oxide is an example.

• Nonmetals share electrons with oxygen, so non-metal oxides are covalent. In water, they act as acids, producing H+ ions and reacting with bases. Tetraphosphorus decaoxide is an example.

Figure on the right classifies the acid-base behavior of some common oxides, focusing once again on the elements in Group 5A, dinitrogen pentaoxide, N2O5, forms nitric acid:

$\displaystyle {{N}_{2}}{{O}_{5(s)}}+{{H}_{2}}{{O}_{\left( l \right)}}\to 2HN{{O}_{3\left( aq \right)}}$

Tetraphosphorus decaoxide, P4O10, forms the weaker acid H3PO4:

$\displaystyle {{P}_{4}}{{O}_{10(s)}}+6{{H}_{2}}{{O}_{\left( l \right)}}\to 4{{H}_{3}}P{{O}_{4(aq)}}$

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The oxide of the metalloid arsenic is weakly acidic, whereas that of the metalloid antimony is weakly basic. Bismuth, the most metallic of the group, forms a basic oxide that is insoluble in water but that forms a salt and water with acid:

$\displaystyle B{{i}_{2}}{{O}_{3(s)}}+6HN{{O}_{3(aq)}}\to 2Bi{{\left( N{{O}_{3}} \right)}_{3(aq)}}+3{{H}_{2}}{{O}_{(l)}}$

Note that as the elements become less metallic across a period, their oxides become more acidic. In Period 3, sodium and magnesium form the strongly basic oxides Na2O and MgO.

Some metals and many metalloids form oxides that are amphoteric: they can act as acids or as bases in water. Metallic aluminum forms amphoteric aluminum oxide (Al2O3), which reacts with acid or with base:

$\displaystyle A{{l}_{2}}{{O}_{3(s)}}+6HC{{l}_{(aq)}}\to 2AlC{{l}_{3(aq)}}+3{{H}_{2}}{{O}_{(l)}}$

$\displaystyle A{{l}_{2}}{{O}_{3(s)}}+2NaO{{H}_{(aq)}}+3{{H}_{2}}{{O}_{(l)}}\to 2NaAl{{(OH)}_{4(aq)}}$

Silicon dioxide is weakly acidic, forming a salt and water with base:

$\displaystyle Si{{O}_{2(s)}}+2NaO{{H}_{(aq)}}\to N{{a}_{2}}Si{{O}_{3(aq)}}+{{H}_{2}}{{O}_{(l)}}$

The common oxides of phosphorus, sulfur, and chlorine form acids of increasing strength: H3PO4, H2SO4, and HClO4.