20分急~化學題 - Ans.fyi 參考答案

20分急~化學題

[匿名]

2011-11-22 6:17 am

The formula for an ore, carnallite,can be represented by KCI.MgCI2.6H2O.when some caranallite is heated with concentrated sulphuric acid,a gas X is produced,
which forms an acidic solution Y when dissolved in distilled water.25cm^3 of solution Y requires 45cm^3
of 1M sodium hydroxide solution for complrtr neutralization.
a)what is gas X?
b)write the equation(s) for the reaction(s) between carnallite and concentrated sulphuric acid.
c)name an indicator which could be used for the titration between solution Y and sodium hydroxide solution,describe its colourchange at the end point.
d)Calculate the molarity of solution Y.

回答 (1)

fooks

2011-11-22 6:31 am

✔ 最佳答案

a)
hydrogen chloride

b)
3H2SO4 + KCl•MgCl2•6H2O → KHSO4 + Mg(HSO4)2+ 3HCl + 6H2O
(Breaking down to two equations are also accepted :)
(H2SO4 + KCl → KHSO4 + HCl)
(2H2SO4 + MgCl2 → Mg(HSO4)2+ HCl)

c)
methyl orange, from red to orange
(or phenolphthalein, from colourless to pale pink)

d)
HCl + NaOH → NaCl + H2O
No. of moles of NaOH = 1 x (45/1000) = 0.045 mol
No. of moles of HCl = 0.045 mol
Molarity of HCl = 0.045 / (25/1000) = 1.8 M

參考: Tsui

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