基准物的称量范围是怎么确定的?为什么?就拿氢氧化钠标准溶液的滴点来说,基准物为邻苯二甲酸氢钾,它的称量范围怎么确定?为何氢氧化钠溶液的体积是20到30mL？

氢氧化钠标准溶液:20~30mL
m=(0.02~0.03)*c(NaOH)*M(邻苯二甲酸氢钾)

Assume concentration of the NaOH solution is close to 0.1 M, and normally you would like to see the second reading on buret somewhere at 35 to 40 mL. Say 40 mL.
Then the mol of NaOH will be 0.1 x 40/1000=0.004 mol
because the reaction is 1:1, so you need same mol of 基准物邻苯二甲酸氢钾.
weight of 邻苯二甲酸氢钾 for each titration will be 0.004 x MW(邻苯二甲酸氢钾.)
You don't want run out the scale of the buret, so you pick some volume safe, say 30 mL.

从你要求的误差来确定范围.假设是要求小于0.1%的误差,那么在称量及滴定时的随机误差不应该大于0.1%.首先是称样的天平,如果是0.1mg的精度,都要求称样量超过0.2g.其次是滴定管,如果精度是0.01ml,要求使用的滴定液体积...