[2022DSE CHEM化學］問答討論區

我嘅理解係喺esterification especially 呢題佢根本唔係dehydrating agent, 你見我啱啱上面嗰段解釋都係當佢catalyst咁解

plus, 你落H2SO4(l)落得幾滴, 但支野個volume大佢咁多, 就算有我都覺得個個dehyrating嘅effect應該好有限

herman yeung ?

不了

我成個實驗解釋一次比你聽啦
(c) (i)
Concentrated sulphuric acid acts as a catalyst, which can speed up the esterification reaction.
但同時conc. sul 都會吸水, 係會shift eqm to the right

(c) (ii)
因為一加左conc sul, 個reaction 會行得好快好快。所以要即刻titrate, 廢事佢react .

(d)
首先, 從stage 2, 可以計到
no. of mole of NaOH
亦即
no. of mole of CH3COOH in the beginning
亦即可以計到 CH3COOH 的concentration
亦即可以計到 CH3CH(OH)CH3 的concentration
呢2個就係個reaction 既initial concentration

stage 1 同stage 2既分別就係
NaOH 係要neutralise d conc. sul
睇下要用幾多NaOH 先夠eutralise d conc. sul

唔該巴打
但仲未明ci 佢ans 講既to prevent disturbance of equilibrium position due to removal of reactant/ to prevent the equilibrium state of reaction shifts to the left due to removal of reactants
佢其實講邊個reaction eqm shift to left?

真係如樓上巴打講下面第1條?
1.CH3COOH⇔CH3COO- + H+
2.CH3COOH + CH3OH ⇔ CH3COOCH3 + H2O


stage 1 同stage 2既分別明了
我都buy你咁講

唔太知點解你份答案咁寫

一加conc. sul 即刻titrate
你問我
只係希望未react 前搵到個initial concentration

巴打有料唔該晒
咁我呢題明白了

你可以睇返我以前d post ...

原來係阿sir

支持啊

其實係dse syl裏面你的確可以當fd係任何時候都可以用
佢嘅壞處就係個過程會比sd慢

唔該晒

唔識分嘅話就係咪都用fd就無死

想問separate mixture of organic compounds e.g hexane and hexanoic acid, 佢地既b.p其實差距都大 係咪其實直接用simple distillation都得?
因為我見會教用 add excess NaHCO3.

可以 sd 會更加方便添

加excess NaHCO3都係無問題嘅 不過繁複少少
因為你係先將hexanoic acid變左 sodium hexanoate
咁就可以isolate hexane去organic layer
跟住做liquid liquid extraction拎hexane
跟住仲要add H+去aqueous layer 出返隻hexanoic acid

不過都要睇下到時候題目有無要求你用啲咩方法/比啲咩apparatus你

謝謝 另外我見 有唔版本 preparation of ester 既steps
版本一係 直接加NaHCO3(aq) 令到 ester floats on water 上面,之後繼續做果啲加drying agent etc

版本二 係先做一次sd 先 收集左ester,而呢個時候既ester 仲未pure ,所以繼續做add NaHCO3 ,drying agent... etc.

想問有無話咩時候 要做一次sd 先 咩時候唔洗,直接加NaHCO3 就得

我估你呢到應該係講緊esterification之後點collect ester
首先我覺得你唔洗點知要點collect嘅
重要都係esterification個part
如果係要講collect嘅話 我見多數都係做distillation先

separation 喺DSE 係非常重要
除左應付core Section 11 之後
未來Analytical Chemistry 一樣需要
而且考得的話，其實都可以幾難攞分

整ester 主要有6個step:
1. Heat the reactants with catalyst under reflux

2. Simple distillation to obtain the organic substances
呢一刻會出現2層immiscible layers
入面會有 你想要既ester, unreacted acid, unreacted alcohol and trace amount of water

3. removal of excess acid
就係用你頭先講既加 carbonate solution

4. removal of excess alcohol
可以用calcium chloride solution remove ethanol

5. removal of trace amount of water
用drying agent e.g. anhydrous calcium chloride

6. 最後再做一次fractional distillation / 或者可以用solvent extraction (An. Chem教)