CHEMISTRY

29 An iron nail is heated with concentrated sulphuric acid. Which of the following combinations is correct?

Gas given off

Color of solution formed

A.

hydrogen

Pale green

B.

hydrogen

Yellow

C.

Sulphur dioxide

Pale green

D.

Sulphur dioxide

yellow

why is D but not C

SO4^2-+4H++2e--->SO2+2H2O

Fe--->Fe2++2e-

fe2+ PALE GREEN= =

1 個解答

評分
  • N70
    Lv 7
    1 十年前
    最愛解答

    Because hot concentrated sulphuric acid is an OXIDIZING AGENT. Thus Iron will be oxidized to Fe3+ ions while sulphuric acid will be reduced to SO2:

    .

    2Fe (s) + 6H2SO4 (aq) → Fe2(SO4)3 (aq) + 6H2O (l) + 3SO2 (g)

    Hence D is correct.

    Pale green solution would be formed when Iron reacts with acids to give Fe2+ ions, e.g. when reacting with DILUTE H2SO4:

    Fe (s) + H2SO4 (aq) → Fe2SO4 (aq) + H2 (g)

    But in such case, Hydrogen, instead of SO2 would be given out. So C cannot be correct.

    Please remember that reactions between H2SO4 & metal will give out:

    - SO2 when H2SO4 acts as an oxidizing agent

    - H2 when H2SO4 acts as an acid

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