F.4 Chemistry~

2010-06-13 10:37 pm

o岩o岩o係考試入面... 有題9分essay題目係話...
Prepare barium sulphate by barium carbonate...
類似咁啦...

所以我寫左用sulphuric acid...
BaCO3(s) + H2SO4(aq) -> BaSO4(s) + H2O(l) + CO2(g)
之後寫左類似話add excess H2SO4 until no colourless gas bubbles come up...
同埋filtrate... crystallization o個o的...

考完之後... 有同學同我講話BaCO3(s) 加 H2SO4(aq) o既話...
因為BaCO3 同BaSO4 都係insoluable... 所以reaction 會stop eventually...
d人話要加dilute nitric或者hydrochloric acid去整到佢soluable... 再加返H2SO4...

不過有d人就講.... "soluability rule都係for water o既姐... 唔關事o既"

咁即係... 我寫話直接用sulphuric acid 會唔會冇分@@!!?

回答 (2)

～

2010-06-17 7:09 pm

✔ 最佳答案

通常呢類 salt preparation essay
都會俾一種insoluble salt 你再去整第2種salt
而通常都係冇可能直接1步過就整到
如果唔係又點樣有6個pt.(ce卷黎講)
而barium carbonate 加sulphuic acid 出黎既個種salt
係barium sulphate 亦都唔溶係水所以層barium sulphate 會form左層protective layer 係barium carbonate 既surface 個reaction 會好快就停左唔能夠好effective地整barium sulphate
如果你直接用sulphuric acid我覺得就應該唔會俾分你.....(請恕我直言)

用excess既 barium carbonate加落dilute nitric acid 出 barium nitrate(to ensure there are no any nitric acid in the solution)
跟住再fillter off the remains
再filtrate mixed with sulphuric acid 錦樣就有d solid form(barium sulphate )
跟住再做多次filitration 分番開佢地再用少少distilled water 沖下d barium sulphate個面再整番乾

參考: my experience

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[匿名]

2010-06-13 11:33 pm

會唔會無分就睇你老師點樣俾你GE JEI
但係你GE答案就係錯GE

因為如果直接加sulphuric acid,
form出黎GE BaSO4 都只係會係表面到形成,
直至到佢完全包實BaCO3之後,
個reaction就會停

所以你個答案係錯ge~

其實一條essay又點會咁簡單問你一個step呢~

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收錄日期: 2021-04-13 17:18:37
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