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现行中学化学教材中,专辟有“两性化合物”一节,所举简明实例为:Al(OH)_3和 Zn(OH)_2,既能溶于酸、又能溶于碱。对此,往往可能产生一种误解,以为两性氢氧化物只能存在于中性介质中。实际情况并非如此。对于不同的两性氢氧化物,其稳定存在溶液的 pH 值不仅是不同的,而且稳定存在溶液的 pH 值也不等于7。那么,究竟怎样确定某两性氢氧化物稳定存在溶液的 pH 值呢?本文拟从化学平衡的角度对此问题作简要说明。
In the current middle school chemistry textbook, there is a section devoted to amphoteric compounds. The concise examples are: Al(OH)3 and Zn(OH)2, which are both soluble in acid and soluble in alkali. In this regard, there is often a misconception that ampholytic hydroxide can only exist in neutral media. The actual situation is not the case. For different amphoteric hydroxides, the pH of their stable solution is not only different, but also the pH of the solution is not equal to 7. So, how do you determine the pH value of a stable solution of an amphoteric hydroxide? This article is intended to give a brief explanation of this problem from the perspective of chemical equilibrium.