[DSE化學2019]同學準備好DSE CHEM未?

呢個我相信佢之後既年份放寬左
你可以睇埋2016 Q6(c)
佢accept H+ + NaHCO3 -> Na+ + CO2 + H2O或H+ + HCO3- -> CO2 + H2O
如果見到佢講明ionic equation既話建議成條full ionc

印象中無記錯的話，係因為你用CaCl2(s) dry NH3(g)既時候，有complexation reaction form咗Ca(NH3)2Cl2(s)，咁你會remove咗NH3，唔係淨係remove water。

巴打而家全職自己教chem 係咪好搵過係補習社好多？

其實冇乜分別

睇你搵唔搵到多學生既補習社姐

概念上NH4NO3係完全water soluble
而且佢個實驗係會add excess KOH to consume all NH4NO3
亦即係話all NH4NO3 in fertilizer會溶曬變aq
咁要寫ionic equation時 只約走個K+而唔約走埋個NO3-喺度就變得不太合理
簡單講 溶水拆得開既就應該拆埋
不過往後既年分都有例外
例如我上面講2016 Q6 (c) (ii)
講lemon juice add to NaHCO3
可以接受NaHCO3 + H+ -> Na+ + CO2 + H2O 或HCO3- + H+ -> CO2 + H2O
不過佢係few drops off lemon juice only 即係未必react曬NaHCO3

當然呢個都係我個人見解 睇下有無老師巴打一齊探討下

唔關事 吸熱唔代表non spontaneous
1dm3水可以溶2kg NH4NO3

Rusting 要記 equation ?

ideal case要closed system
因為vapor pressure會影響liquid既volatility
不過一般實驗(特別中學)廢事煩 無gas species involve就唔密封

最好啦
最低限度要知過程中Fe既變化

yes perfect equilibrium黎講must be closed system(no substances in or out)
但我好懷疑佢會唔會咁問
因為一般中學生做lab d老師為左簡化setup
通常都唔會整到完全closed system
變左大部分學生既認知未必會咁嚴謹

考試同實際始終無可避免有差別 又要考慮埋大眾考生既認知範圍
d日成日屌出題出得差
輪到比你出題時 其實好多要素考慮
要有效評級而又fair 有時我覺得無可厚非

Presence of Mobile ion increase rate of corrosion is due to both increase in electrical conductivity of metal and increase in electrical conductivity of water ?

點解 zinc planting 當 coating 未被 damaged 果陣 Zn 係唔會 lose e to Fe?

同樣地點解 tin plant 當 coating 未被 damaged , Fe 唔會 lose e to Ti?

好亂

2樣都無oxidized到所以唔會donate到e-過去?

類似anodization 都有層protective oxide layer
阻隔air contact with Fe

solution only
metal本身已係conductive