Magnesium ribbon was added to each of the following aqueous solution in turn: H2SO4, AgNO3, HNO3, HCl, NH3, HCl, NH3. In which case does the magnesium become covered with a dark precipitate?
a
H2SO4
b
AgNO3
c
HNO3
d
NH3
e
HCl
Explanation
Correct Option
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joanj
2 years ago
The correct answer is C. HNO3.
When magnesium ribbon is added to nitric acid (HNO3), it reacts to form magnesium nitrate and nitrogen dioxide gas. The presence of nitrogen dioxide gas can give the appearance of a dark precipitate on the surface of the magnesium ribbon, leading to the perception of a dark coating. The reaction is as follows:
3Mg(s) + 8HNO3(aq) -> 3Mg(NO3)2(aq) + 2NO2(g) + 4H2O(l)
The nitrogen dioxide gas formed in this reaction is brown in color, which may give the impression of a dark precipitate covering the magnesium ribbon.
