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一、例题评析例1若以ω1和ω2分别表示浓度为amol·L-1和bmol·L-1的氨水的质量分数,且已知2a=b,则下列推断正确的是().(氨水的密度比纯水的小)A.2ω1=ω2B.2ω2<ω1C.ω2>ω1D.ω1<ω2<2ω1解析:设溶液的体积为VL,密度为ρg·cm-3,溶质的摩尔质量为Mg·mol-1,质量分数为ω,物质的量浓度为cmol·L-1.从不同的角度表示溶液的浓度,其表达式不同,但溶质守恒(包括溶质质量守恒、溶质物质的量守恒).有n=Vc=V×103ρω/M,即c=1000ρω/M.依题意有a=
I. Example Evaluation Example 1 If ω1 and ω2 represent the mass fractions of ammonia in concentrations of amol·L-1 and bmol·L-1, respectively, and 2a=b is known, the following inference is correct (). (Ammonia The density is lower than that of pure water.) A.2ω1=ω2B.2ω2<ω1C.ω2>ω1D.ω1<ω2<2ω1 Analysis: Let the volume of the solution be VL, the density be ρg·cm-3, and the molar mass of the solute be Mg. ·mol-1, the mass fraction is ω, and the concentration of the substance is cmol·L-1. The concentration of the solution is expressed from different angles, and its expression is different, but the solute is conserved (including the conservation of solute mass and the conservation of solute mass) There is n=Vc=V×103ρω/M, that is, c=1000ρω/M.