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在初中化学第六章《铁》中常出现这么一类选择题:某不纯金属与稀酸反应生成一定质量的氢气。求不纯物质中可能是由哪些金属组成的。面对这类习题,不少同学不知从何入手。下面针对一些习题探讨一下这类题的解法。 一、假设估算法 例1 5.6g不纯的铁粉与足量稀硫酸反应生成0.2g氢气。下列情况可能是( )。 (A)铁中含有碳和锌 (B)铁表面有铁锈 (C)铁中含有碳和铝 (D)铁中含有碳 解析:先假设5.6g不纯铁粉是纯铁粉,则完全反应生成0.2g氢气。恰好与5.6g不纯铁粉生成的氢气相等,从而我们估算不纯的5.6g铁粉中所含的杂质金属一定比等质量的铁放出的氢气多。观察选项中提供的金属混合物一定含有铝,但要使等质量的铝和铁放
This type of multiple-choice question often appears in the sixth chapter of the junior high school chemistry “iron”: an impure metal reacts with dilute acid to produce a certain amount of hydrogen. What metal may be involved in the impure substance? In the face of such exercises, many students do not know where to start. The following is a discussion of some solutions to these problems. I. Hypothetical estimation method Example 1 5.6 g of impure iron powder reacts with sufficient amount of dilute sulfuric acid to produce 0.2 g of hydrogen gas. The following may be (). (A) Iron contains carbon and zinc (B) Iron has rust on the surface (C) Iron contains carbon and aluminum (D) Iron contains carbon Analytical: Assume that 5.6 g of impure iron is pure iron and reacts completely. Generate 0.2g hydrogen. It is exactly equal to the hydrogen produced by 5.6 g of impure iron powder, so we estimate that the impure metal contained in the impure 5.6 g iron powder must be more than the equivalent mass of iron. The metal mixture provided in the observation option must contain aluminum, but the same quality of aluminum and iron