The following results, were obtainted through a series of two experiments: Exper
ID: 796036 • Letter: T
Question
The following results, were obtainted through a series of two experiments:
Experiment 1: Reactions with acids
Cr (S)
Ag (S)
HCl
Metal dissolves, bubbles, green solution
No apparent reaction
H2SO4
Metal dissolves, bubbles, bluish purple solution
No apparent reaction
Experiment 2: Replacement reactions
Cr2+ + Ag metal: no apparent reaction, silver metal did not change, solution stayed green
Ag+Cr metal: silvery solid formed on piece of Cr metal. Solution went from colorless to bluish-green.
a) Write the total net ionic equations that desbribe all of the results noted form Experiment 1 and Experiment 2.
b) Explain the color changed observed in Experiment 2 (replacement reactions)
c) Discuss the relative activites of silver and chromium.
Cr (S)
Ag (S)
HCl
Metal dissolves, bubbles, green solution
No apparent reaction
H2SO4
Metal dissolves, bubbles, bluish purple solution
No apparent reaction
Explanation / Answer
These reactions are complicated, because you form hydrates of the chromium ions. In HCl, you form a complex of the chromium ions with both water and chloride, making the solution green, whereas in sulphuric acid, the complex is with water only, making the solution purple.
Full equation: 2Cr(s) + 6HCl(aq) + 8H2O(l) ? 2[CrCl2(H2O)4]Cl(aq) + 3H2(g)
Net ionic: 2Cr(s) + 6H^+ + 4Cl^-(aq) + 8H2O(l) ? 2[CrCl2(H2O)4]^+(aq) + 3H2(g)
Full equation: 2Cr(s) + 3H2SO4(aq) + 12H2O(l) ? [Cr(H2O)6]2(SO4)3(aq) + 3H2(g)
Net ionic: 2Cr(s) + 6H^+ + 12H2O(l) ? 2[Cr(H2O)6]^3+ + 3H2(g)
Silver does not react with acids unless they are powerful oxidising acids (such as concentrated nitric acid).
In the replacement reaction, silver ion is a more powerful oxidising agent than chromium ion. Therefore, when chromium wire is dipped in a silver ion solution, the chromium will displace the silver, forming green Cr^3+ ions and silver metal.
3Ag^+(aq) + Cr(s) ? Cr^3+(aq) + 3Ag(s)
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