Hydroxides 1. Mix about 2 ml of 1 M NaOH with about 1 ml of FeSO4. What precipit
ID: 977221 • Letter: H
Question
Hydroxides
1. Mix about 2 ml of 1 M NaOH with about 1 ml of FeSO4. What precipitate forms initially? Write a chemical equation for the reaction. Pour the solution and precipitate into a watch glass. Let sit for about 1/2 hour to react with O2 from the air. This generates the more darkly colored Fe(OH)3(s). Write a balanced equation for this reaction.
Iron and ferri/ferrocyanide:
2. (step 1) In one test tube place several mL flute Fe(II), and in another dilute Fe(III). To each test tube add several mL of 0.1 M ferrocyanide K4Fe(CN)6.
(step 2) Repeated above step using 0.1 M ferricyanide, K3Fe(CN)6 instead of ferrocyanide.
Ferric ferrocyanide is a dark blue precipitate with the formula Fe4[Fe(CN)6]3. Ferrous ferrocyanide is a white precipitate with the formula K2Fe2(CN)6. Write balanced reactions for the mixtures in steps 1 and 2. (two reactions for each step).
Knowing that oxygen is an oxidizing agent, Why is your white precipitate slightly blue?(write reaction)
Explanation / Answer
Hydroxides,
1. FeSO4 reacts with added hydroxide to form Ferrous hydroxide,
Fe2+ + 2OH- ---> Fe(OH)2
When solution is left under air, Fe2+ gets oxidized to Fe3+ and the new hydroxide is ferric hydroxide,
Fe2+ ----> Fe3+
Fe3+ + 3OH- ---> Fe(OH)3
Iron ferri/ferrocyanide
2. reaction with Fe2+/Fe3+
Fe2+ + KCN ----> K4[Fe(CN)6] (white)
Fe3+ + KCN ---> K3[Fe(CN)6] (blue)
Fe2+ gets oxidized to Fe3+ in air. Incomplete oxidation leads to formation of K4[Fe(CN)6] contaminated with K3[Fe(CN)6], which gives a white ppt with a slight bluish coloration.
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