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General Chemistry Principles, Patterns, and Applications, 2011

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in Chapter 16 "Aqueous Acid–Base Equilibriums",Section 16.1 "The Autoionization of Water").<br />

Amphoteric oxides either dissolve in acid to produce water or dissolve in base to produce a soluble<br />

complex. As shown in Figure 17.9 "Chromium(III) Hydroxide [Cr(OH)", for example, mixing the<br />

amphoteric oxide Cr(OH)3 (also written as Cr2O3·3H2O) with water gives a muddy, purple-brown<br />

suspension. Adding acid causes the Cr(OH)3 to dissolve to give a bright violet solution of Cr 3+ (aq), which<br />

contains the [Cr(H2O)6] 3+ ion, whereas adding strong base gives a green solution of the [Cr(OH)4] − ion. The<br />

chemical equations for the reactions are as follows:<br />

Equation 17.28<br />

Cr( OH )3 s<br />

Equation 17.29<br />

Cr( OH )3 s<br />

( ) + 3H + ( aq) ® Cr3+ ( aq) violet + 3H2O( l)<br />

( ) +OH - ( aq) ®[Cr OH<br />

( )4]- green aq<br />

Figure 17.8 Classification of the Oxides of the Main Group Elements According to Their Acidic or<br />

Basic Character<br />

( )<br />

There is a gradual transition from basic oxides to acidic oxides from the lower left to the upper<br />

right in the periodic table. Oxides of metallic elements are generally basic oxides, which either react<br />

with water to form a basic solution or dissolve in aqueous acid. In contrast, oxides of nonmetallic<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

1601

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