论文部分内容阅读
化学题中的隐蔽条件,常以各种形式匿伏在文字叙述中,本文以初中化学习题为例,谈谈挖掘习题中隐蔽条件的几种途径。1 从化学概念的内涵挖掘隐蔽条件 例1 t°时,将A溶液在温度不变的条件下蒸去50克水,有12克A晶体析出(晶体中无结晶水);再蒸去20克水,又有8克A晶体析出。如果再蒸去50克水,又有多少克晶体析出? 解析:有的同学可能会脱口而出:“又有12克A晶体析出。”实际上,他忽略了蒸发水时原溶液是否饱和的问题。此题的隐蔽条件是“析晶后的溶液是饱和溶液”,抓住这一点,便可列式求解,设第三次蒸发时有x克A晶体析出,则有
The hidden conditions in chemistry questions often hide in textual narratives in various forms. This article takes the junior middle school chemistry problem as an example to discuss several ways of mining hidden conditions in the exercises. 1 When digging out the concealed conditions in the connotation of the chemical concept 1 t°, dissolve the A solution with 50 g of water under the same temperature, and precipitate 12 g of crystals (no crystalline water in the crystals); In water, another 8 grams of A crystals precipitated. If we evaporate 50 grams of water again, how many grams of crystals will precipitate? Analysis: Some students may blurt out: “Another 12 grams of A crystals precipitated.” In fact, he ignored the problem of whether the original solution was saturated when water was evaporated. The hidden condition of this question is “the solution after devitrification is a saturated solution”. If this is the case, the solution can be solved. If the third evaporation occurs, there are x grams of A crystals precipitated.