引用第8樓danhon於2006-11-03 20:41發表的“”:
現階段覺得CHEM最難....=.="
成日做titration....
有時唔知點find個end point 先準<----big problem!!
.......
titration 算係易做架喇~
個lab report 講黎講去都係個d嘢,d數又係差唔多咁計~
當你遲d做得多其他類型既實驗之後,你見倒有titration就會好開心添~
end point準唔準...都係睇你d技巧....同埋唔好心急!
首先你當然要知道你用緊咩indicator,end point會有咩colour change...
最煩/慢都係做trial個次,你真係唔知大概要落幾多...
跟後你都可以計一計,落定一定既份量,然後再慢慢落...
做到接近end-point,當你唔肯定個個係咪end-point個陣,
eg. phenolphalein.....from red to pink(end-point)
你唔肯定個個係咪pink,
你可以先take reading(r1)
然後再落多少少,如果即刻無色,你就用r1
如果仲係有色(pink/red)....你再take reading(r2)
.......如此類推,做到佢無色,你就用你最後take 個個
當然e個reading都唔係最準,e個係titration本身一個不可避免既error(intrinsic error)
For example Ａ+ + Ｂ-(titra) --> AB
when the reaction near it's end point, the A+ in the solution is in very small amount that a drop of B- is in excess to react with all A+. Thus, B- is slightly in excess(unavoidable)
仲有....通常d titration 既 reaction 既rate都係好快(當然你都係要搖個conical flask架啦 ).....
但係有時有d都會幾慢下...你以為已經做倒個end point,但過一陣佢可能又會變色....原來佢一早就已經過左end point......要留意下(thus why u need to pre-lab!) |
