Other cations in addition to Al^+3 from amphoteric hydroxides. Using the provide

Question

Other cations in addition to Al^+3 from amphoteric hydroxides. Using the provided solutions, determine experimentally if they form soluble complex ions with sodium Using 1-2 mL of each solution, first add NaOH drop wise until a precipitate appears. a Then attempt to dissolve the precipitate by adding excess NaOH. If a complex ion forms, write the probable formula for that complex and amp heretic anion formula. The aluminum ion is done for you as an example. Refer to your text or an online site (search for "complex ion formation constants') for help with the complex ion formulas. Write the colors and formulas of the hydroxide precipitates which do not dissolve in excess strong base. You will notice that the zinc hydroxide precipitate dissolves both in ammonium hydroxide and in sodium hydroxide. Now, perform the following experiment. Place 5 mL of 0.1 N Zn(NO_3)_2 in each of two small beakers. To one beaker, add NaOH drop wise with shaking until the zinc hydroxide precipitate first formed has almost, but not quite, dissolved. Avoid an excess of NaOH. To the second add NH_4OH also drop wise, until the zinc hydroxide precipitate has almost, but not quite, dissolved. Avoid excess NH_4OH. Now, using the pH meter, determine the pH in each beaker. From your results, state and explain your answer to the original problem. pH solution 1 (with NaOH): pH solution 2 (with NaOH): When Zn(OH)_2 dissolves in ammonium hydroxide, does it form a hydroxide complex or an ammonia complex? You assumed an answer to this question in part C. Explain how these data support the assumption made in part C.

Explanation / Answer

Al3+      Al(OH)3

whilte

Mn^2+ Mn(OH)2

Pink

does not dissolve

Co^2+    Co(OH)2

blue

does not dissolve

Ni^2+   Ni(OH)2

green

does not dissolve

Cr^3+      Cr(OH)3

green

does not dissolve

Pb^2+    Pb(OH)2

white

PbO2^2-

Fe^3+      Fe(OH)3

brown

does not dissolve

Zn^2+     Zn(OH)2

white

ZnO2^2-

(complex ion)

Al3+      Al(OH)3

whilte

Mn^2+ Mn(OH)2

Pink

does not dissolve

Co^2+    Co(OH)2

blue

does not dissolve

Ni^2+   Ni(OH)2

green

does not dissolve

Cr^3+      Cr(OH)3

green

does not dissolve

Pb^2+    Pb(OH)2

white

PbO2^2-

Fe^3+      Fe(OH)3

brown

does not dissolve

Zn^2+     Zn(OH)2

white

ZnO2^2-

(complex ion)

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