问题 问答题

9.5gMgCl2固体溶于水配成500mL溶液,其浓度为______mol•L-1,从中取出100mL溶液,其中Cl-的浓度为______mol•L-1;再把取出的溶液加水稀释成500mL,则此时MgCl2溶液的浓度为______mol•L-1

答案

9.5gMgCl2的物质的量=

9.5g
95g/mol
=0.1mol,故氯化镁溶液的浓度为
0.1mol
0.5L
=0.2mol/L;

溶液是均匀的,从中取出100mL溶液,其中Cl-的浓度与原溶液相同,溶液中c(Cl-)=2c(MgCl2)=2×0.2mol/L=0.4mol/L;

根据稀释定律,稀释前后氯化镁的物质的量不变,令稀释后MgCl2溶液的浓度为cmol/L,则:

0.2mol/L×100mL=cmol/L×500mL,解得c=0.04,

故答案为:0.2;0.4;0.04.

阅读理解

阅读理解。

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