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巧用逆向思维解化学题
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  3. [发布时间:2021-06-19 10:11]

  逆向思维是一种与习惯性和常规性思维方向背道而驰的思维活动。属于创造性思维。在很多情况下 倒过来思考问题,在思考过程中“做相反的事情”。可以使人们获得许多通常无法通过思考获得的思考结果。一位年轻的司马光(Sima Guang)打破战车救了他的同伴的故事,这是巧妙运用逆向思维的典型例子。现在,我将讨论在化学问题解决过程中如何巧妙地运用逆向思维。

  1。 使用逆向思维做出明智的判断

  逆向思维是一种思维方法,可以训练学生善于从对问题的积极思考转变为对立或相反。它可以帮助我们理解和判断这个概念。

  E.G,了解价后,经常遇到这样的概念上的判断:

  元素显示化合物中的化合价。()

  [分析]目前, 只是反过来考虑一下:化合物中是否有一种元素可以显示多个化合价?例如, 想到硝酸铵中的氮元素分别显示为-3和+5价,我们很容易做出正确的判断,这句话是错的。

  这种反向思维方法通常用于研究其他基本概念。例如判断以下陈述是对还是错:

  (1)如果两种化合物反应形成另外两种化合物, 化学反应必须是易位反应。()

  只要从逆向思维的角度来看,查找示例2NaOH + CO2 == Na2CO3 + H2O,这也是化合物与化合物之间产生另外两种化合物的反应,但是在反应过程中没有成分的交换,您可以做出判断。

  (2)质子数相同的粒子必须是相同的元素。()

  只要质子数相同的粒子不是同一元素,就可以反驳这一主张。例如, 具有10个质子的粒子是H2O, NH3, 娜, 等等。,它们是不同的元素。

  第二, 明智地选择逆向思维

  化学中存在一些问题,需要根据给定条件通过逆向思考找到解决问题的关键。确定解决问题的计划。善于运用逆向思维解决问题,解决问题的速度不仅很快,而且方法很好。

  例如:4克的锌粉混合物, 铁粉 镁粉与一定质量的25%稀硫酸反应完全。水蒸发后取100克固体物质,则产生的氢的质量为()

  一种, 2克B, 3克 4 g D, 5克

  [分析]如果这个问题采用积极思考, 锌的质量 铁, 将镁和镁分别设置为未知数以进行分析和计算。这个过程很复杂,还有更多线索。使用逆向思维, 该分析基于以下思路:反应前后每个元素的质量均保持不变。从问题的意义来看, 我们可以看到所有三种金属:锌, 铁, 和镁参与反应。硫酸锌 硫酸铁 和硫酸镁分别形成,在100克固体物质(硫酸锌的混合物中, 硫酸铁 and magnesium sulfate) obtained after evaporating the water,Containing three elements of zinc, iron, and magnesium, the total mass is 4 g,The other 96 g is the mass of SO4,Then according to the relationship between H2 and SO4 in the reaction,The mass of hydrogen produced is calculated to be 2 g.

  This shows that reverse thinking is very useful for cultivating flexibility and sensitivity of thinking.

  3. Fill in the blanks with reverse thinking

  Reverse thinking is an important way of thinking in logical thinking.It is to understand the problem from the opposite direction of conventional thinking,Think about the problem from the opposite perspective,To achieve the effect of making it easier to achieve, and getting twice the result with half the effort.Students are often used to positive thinking from the known to the unknown,Over time,It is easy to form a positive mindset,For a kind of multiple-choice questions that are difficult to solve from positive thinking,Can convert an angle,Assuming that a certain conclusion is correct,Reversely infer whether the dry conditions of the question hold,So as to determine whether the null hypothesis is true.

  For example: two metals of equal mass, M and N, react with sufficient dilute sulfuric acid respectively,Both produce + divalent metal sulfate and hydrogen.The relationship between the mass of hydrogen generated m (ordinate) and the reaction time t (abscissa) is shown on the right ()

  (1) Compare the activity of M and N metals

  (2) The conclusions that can be drawn from the two straight lines in the figure are

  [Analysis]This question gives the curve of the mass and time of hydrogen generated when the metal reacts with acid.Many students will feel unable to start,If you think in the opposite direction: the faster the curve rises,It shows that the more violent the metal reacts with dilute hydrochloric acid,The greater the mobility of the metal.At the same time, it can be seen from the figure that the mass of hydrogen produced by M is more than that of N,It takes less time to complete the reaction.

  Third, 用逆向思维巧妙地推断

  涉及物质相互转化为初中化学主要内容的推论,使用逆向思维来推断是非常有效的,解决问题的想法:把握突破点→加强层次→得出结论

  例如:从下图推断(假设所有可能发生的反应均已完成)

  (1)如果B是水,那么A是; (填写化学式)

  (2)如果B是酸性溶液,那么A是; (填写化学式)

  (3)写下C和BaCl2溶液之间反应的化学方程式:

  [分析]如果这个问题难以沿着变化的方向解决,如果是逆向思维,那是, 从更改结束解决问题要容易得多。解决元素复合推理问题,有必要抓住物质的特征反应作为解决问题的突破,红褐色沉淀物F F为Fe(OH)3。 复分解反应的特征性黄色溶液为FeCl3。 有色溶液C与BaCl2溶液反应生成白色沉淀物D和FeCl3溶液, 白色沉淀物D不溶于稀硝酸。 白色沉淀物D是BaSO 4。有色溶液C为Fe 2(SO 4)3。因此,该问题可以容易地解决。

  四 用逆向思维巧妙地计算

  为了解决这个问题, 必须首先检查问题,在复习问题时, 我们使用逆向思维的方法,开始思考问题,找到问题需要什么条件,有条件吗?可以根据问题的条件获得不符合条件的条件, 等等。,这样, 解决问题的方法和方法可以顺利找到。

  例如:在CO和CO2的混合气体中,氧元素的质量分数为64%,使混合气体5㎏通过足够量的热氧化铜,充分反应后,然后将所有气体通入足量的澄清石灰水中,What is the mass of the white precipitate obtained?

  [Analysis]If this question is done step by step,There are many reactions involved,More data,Cumbersome calculations,Error-prone.And if you grasp that the final reaction product is calcium carbonate,Adopt reverse thinking,Find out the C-CaCO3 conservation relationship between calcium carbonate and the starting reactant CO and CO2 mixed gas,It's very easy to get out of "heavy mountains and rivers",Usher in the "willows and flowers".

  5. Use reverse thinking to read life skillfully

  Life is full of scientific knowledge,Some phenomena in life often prompt us to think.Such as: Why can soap decontaminate?Why does gas poisoning occur?Why do rotten apples (potatoes, sweet potatoes, etc.) smell of alcohol?How many anti-rust measures does your bike have?Why are the festival fireworks colorful?Why do words written in blue and black ink appear blue first and then turn black?As long as we are a caring person in life,Observe and think carefully,Can always lead the problem to the "reverse",Improve the ability of reverse thinking,Let us gallop in the kingdom of reverse thinking.

  Reverse thinking is relative to habitual thinking,That is, the thinking method of thinking about problems from the opposite direction,It often has surprising effects.Reflects that when the positive thinking is in the dilemma of "there is no way out of the mountains and rivers",Through reverse thinking, the beauty of "a village with bright flowers and bright flowers" will often appear.

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