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极值法也叫极端法.一般适用于有关混和物或决定取值范围的计算.把题设中几种物质的总量假设成只含某一物或某二物的质量再按题意求解,然后据求出的数值作出正确的判断.例1.在50克含有1.17克氯化钠和0.84克氟化钠的溶液中滴入过量的AgNO_3溶液,充分搅拌,静置,过滤,洗涤,干燥,称量得到2.87克固体.由此可以得出的正确结论是(A)氯离子只有一部分参加反应(B)氟离子只有一部分参加反应(C)氟化银难溶于水(D)氟化钠与硝酸银在溶液中无沉淀生成分析:此题的目的在于用定量实验推断物质(AgF)的性质(溶解性).当加入足量AgNO_3时Cl~-肯定全部沉淀,至于F~-能不能转化成AgF沉淀则应视题日中2.87克沉淀量与Cl~-完全沉淀的沉淀量的关系确定.如果Cl~-完全沉淀生成的沉淀量小于2.87克,则F~-也变为AgF沉淀了.如Cl~-完全沉淀生成的沉淀量等于2.87克,则AgF溶于水.故Cl~-完全沉淀就是一种极端情况,生成AgCl的质量也为一极值.
The extremum method is also called the extreme method. It is generally applied to the calculation of the mixture or the determination of the range of values. The total amount of several substances in a question is assumed to contain the mass of only one thing or two and then to solve the problem. , And then make a correct judgment based on the calculated value. Example 1. Into a solution of 50g containing 1.17g of sodium chloride and 0.84g of sodium fluoride, add an excessive amount of AgNO 3 solution, stir well, let stand, filter and wash. It was dried and weighed to give 2.87 g of solid. The correct conclusions that can be drawn from this are (A) only part of the chloride ions participate in the reaction (B) only part of the fluoride ions participate in the reaction (C) silver fluoride is hardly soluble in water (D) fluoride Sodium and silver nitrate in the solution without precipitation analysis: The purpose of this question is to use quantitative experiments to infer material (AgF) properties (solubility). When adding sufficient amount of AgNO_3 Cl~- sure all precipitate, as for F~- The ability to convert to AgF precipitation should be determined by the relationship between the 2.87 g precipitation and the amount of Cl~-precipitated sedimentation, assuming that the total amount of Cl~-precipitation is less than 2.87 g, then F~- becomes AgF precipitated. If Cl~-precipitate is equal to 2.87 grams, AgF dissolves in water. So Cl~-complete precipitation is Kind of extreme, generate AgCl quality is also an extreme value.