回應(AL)

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Or:
i want to know why to use P2O5for drying a moist sample of C2H5COOH?THX~

化學友:
Or,化學友覺得你條問題同 AL 2003 Paper I 8 一樣o架:

The following compounds can be used as drying agents:

Na2SO4(s), NaOH(s), CaCl2(s) and P2O5(s)

Choose, from the above, one compound which is most suitable and effective

for drying a moist solid sample of C6H5CO2H.

NaOH 就一定唔得啦，因為acid (C6H5CO2H)同alkali(NaOH)有reaction。化學友都check過書，P2O5真係standard嘅drying agent for C6H5CO2H，但係就冇講why Na2SO4 and CaCl2 cannot。至於街外嘅solution guide嘅解釋又似乎有好多漏洞。(化學友有時唸會唔會Na2SO4 同CaCl2 用於C6H5CO2H嘅drying power唔係太好呢?)

街賣嘅pastpaper嘅answer係話P2O5，但據化學友所知當時嘅AL exam係接受下面三個答案:
P2O5(s) / Na2SO4(s) / CaCl2(s)

各位如果知explanation嘅話，留言比我丫。