[2022DSE CHEM化學］問答討論區

有冇唔記得計埋 H2O(l) 個concentration 呀 ?

Esterification 當然計埋
但呢條好似唔係咁typical
睇完answer都唔識

send answer ok ?
好難搵 AS d marking

Specific d 咁問，17.15-（36.9 -36.8 ）其實係咩意思

因為organic acid個ionization係reversible
所以你攞啲H2SO4落去會影響到個equilibrium position
所以要用咗之後嘅數據減落之前個數據消除翻個error to obtain a more accurate result

想問下樓主使唔使識different catalyst 嘅catalytic power嘅差距
e.g. Fe(NO3)3 同 MnO2對於 H2O2嘅decomposition嘅effect
同埋想請問宜家syl 係咪多咗phenolphthalein 高過pH=14嘅時候會變透明同埋tooth paste experiment兩樣野要讀

想問d答案喺邊度搵
我去埋圖書館都搵唔到AS 答案

使唔使識different catalyst 嘅catalytic power嘅差距
唔使

係咪多咗phenolphthalein 高過pH=14嘅時候會變透明
唔係

係咪多咗tooth paste experiment
不嬲都有
係suggest 老師教rate of reaction 可以用既experiment 之一

different catalyst catalytic power嘅分別唔需要識

tooth paste experiment呢個term我未聽過
但裡面嘅化學反應係雙氧水出水同氧 我相信dse有機會出呢個reaction 但至於你話讀 我認為無野要讀 純粹佢會拎呢個reaction黎出一啲題目 例如redox

Phenolphthalein pH高過14都當係pink
唔會係透明

原則上係要認識呢個reaction
即係decomposition of hydrogen peroxide
亦即要寫得出條equation

因為其實我未特別聽過講呢個term
純粹個reaction會係題目討論
做redox/rate嘅題目都常見
不過知埋個名都無壞

佢寫錯名姐
比較common 既名係elephant toothpaste
事實上係decomposition of hydrogen peroxide
加左catalyst (MnO2) 之後, 個reaction 變得好快

做呢個實驗通常會落detergent
出勁多oxygen
比d detergent 包住就會變成好多泡泡
如果用個窄身既measuring cylinder 做就會一柱擎天了

亦因為reaction 係超級exothermic
所以d 水亦會好快變steam
實驗效果更好

你講ci 果到
加H2SO4 係抽水
Ans點解係eqm shift to left 唔係shift to right

AS 我黎緊都會開始做solution，1994-2002 所有題目

宜家有兩條
1.CH3COOH⇔CH3COO- + H+
2.CH3COOH + CH3OH ⇔ CH3COOCH3
加H2SO4唔係抽水呀,考評局已經講過H2SO4係esterification個作用係catalyst而唔係dehydating agent
你想像吓, 就算佢真係可以抽水, 啲水咪都係留喺個flask(system)入面, 其實係唔會有影響
你加acid會影響到第一條個equilibrium position, 令到[CH3COOH]多咗, 第一條式個eqm position 咪shift to the left
同埋[CH3COOH]多咗, 你用實驗數據計嘅第二條式個Kc咪唔準
所以要用落咗之後個titration result減之前

好感謝您 但唔知點解見到本書話pH≥14 佢會turns colorless slowly

好的感謝您

巴打多謝你覆先
conc. H2SO4大家都知一定係Catalyst
但我講緊catalyst 以外仲有個係dehydrating property
但唔記得左邊年PP睇到 搵唔返了..
得d網上濕鳩source:
Concentrated sulfuric acid is used as a catalyst, and has a dual role:
- Speeds up the reaction.
- Acts as a dehydrating agent, forcing the equilibrium to the right and resulting in a greater yield of ester.

https://easychem.com.au/the-acidic-environment/esterification/esterification-and-catalysis/

Ching我知呀
但18年定唔知19年之後考評局就已經唔當佢嘅function有act as a dehydrating agent了, 所以你睇之前啲PP可能仲會話佢係

又或者你真係唔肯定可以問翻老師, 我都係今年考可能都會錯

如果以前18年之前當係dehydrating agent
咁點解ASL 00果條pp又唔當係dehydrating agent

自修生冇老師