1.When substance Y is treated with an aqueous solution of iron(III) nitrate, the iron(III) ions act as oxidizing agent. Y may be
A. Sodium hydroxide solution
B. Potassium iodide solution
C. Acidified potassium permanganate solution
D. Magnesium ribbon
the ans given is D, but why the answer cannot be B? KI is also a reducing agent.
2.Which of the following substance can be used to distinguish between dilute hydrochloric acid and dilute sulphuric acid?
A. Magnesium ribbon
B. Sodium hydrocarbonate solid
C. Copper(II) oxide
D. Silver nitrate solution
the ans given is D. But i think Ag+ will also form ppt with SO42-.
Why the answer cannot be A? Mg gives gas bubbles at a faster rate with H2SO4 than HCl?
2條CHEM MC(急)
2013-03-30 4:57 pm
回答 (2)
2013-04-01 6:58 pm
✔ 最佳答案
Q1:The answer cannot be B because although iodide ion in KI is reducing agent, it has not enough reducing power to reduce iron(III) ions. You can refer to electochemical series and you will find that iron(III) ion is above iodine, hence no redox reaction occur.
Q2:
In DSE syllabus, AgSO4 is considered as soluble compound in water,but in fact it is very slightly soluble(0.31 g/100 mL),yet you can regard that it is soluble in water.
Option A is incorrect because the question do not provide the information about the concentration of two acids and hence you cannot determine which acid has higher concentration of hydrogen ions in this case.
2013-04-01 16:45:40 補充：
In the first question, option B can also be the answer as iodide ions can reduce iron(III) ions into iron(II) ions.Sorry for my carelessness.:)
參考: Wiki
2013-04-02 6:55 am
According to some source,
std. reduction potential of Fe(3+) to Fe(2+) = +0.771V
std. reduction potential of I2 to I(-) = +0.554V
overall std. cell potential = 0.771 - 0.554 which is positive;
so, oxidation of iodide by iron(III) is feasible.
std. reduction potential of Fe(3+) to Fe(2+) = +0.771V
std. reduction potential of I2 to I(-) = +0.554V
overall std. cell potential = 0.771 - 0.554 which is positive;
so, oxidation of iodide by iron(III) is feasible.
收錄日期: 2021-04-16 15:40:49
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