I’m having a very hard time with this section, mainly the questions about the ca

Question

I’m having a very hard time with this section, mainly the questions about the cations in the filtrate and precipitate. CHEM 1212L Lab Manual-Page 44 Post Lab Questions Answering these questions wil help you develop a flow chart and a strategy for the Qualitative Analysis of an Unknown Lab 1. You have a solution that contains the following cations: Ag', K' and Fe"3. You first add a few drops of 1 M HCI to the mixture. a. What will you observe? Include colors and appearance. b. What cations, if any, will be present in the filtrate? c. What cations, if any, will be present in the precipitate? drops of 3 M H2SO4 to the liquid obtained above. 2. After centrifuging and separation of the layers obtained above, you add a few a. What will you observe? Include colors and appearance. b. What cations, if any, will be present in the solution? c. What cations, if any, will be present in the precipitate? 3. Again, after centrifuging and separation of the layers obtained in step two above, you add 2 M NaOH to the liquid obtained above until the solution is slightly basic. a. What will you observe? Include colors and appearance. b. What cations, if any, will be present in the solution? c. What cations, if any, will be present in the precipitate?

Explanation / Answer

1a) Ag+, K+ and Fe3+ all react with HCl. The solution will be yellow due to the formation of FeCl3 with a cloudy white precipitate of AgCl. KCl is a colorless salt and dissolves in the solution. The reactions taking place are:

Ag+ (aq) + HCl (aq) --------> AgCl (s, white) + H+ (aq)

K+ (aq) + HCl (aq) --------> KCl (aq) + H+ (aq)

Fe3+ (aq) + 3 HCl (aq) -------> FeCl3 (aq, yellow) + 3 H+ (aq)

b) The filtrate will contain the soluble salts. KCl and FeCl3 are the soluble salts and hence, the filtrate will contain K+ and Fe3+ ions.

c) The precipitate will contain white AgCl and hence, Ag+ ions are present in the precipitate.

2a) When H2SO4 is added to the filtrate, the solution remains yellow; at best, the yellow color of the solution fades slightly due to dilution effect.

b) H2SO4 forms soluble Fe2(SO4)3 and K2SO4 and hence, the solution will contain K+ and Fe3+ ions.

c) No precipitation is observed with the addition of H2SO4.

3a) The solution turns brown due to the formation of brown colored Fe(OH)3. KOH is also formed; but KOH is colorless. The reactions taking place are:

Fe2(SO4)3 (aq) + 6 NaOH (aq) ---------> 2 Fe(OH)3 (s, reddish brown) + 3 Na2SO4 (aq)

K2SO4 (aq) + 2 NaOH (aq) --------> 2 KOH (aq) + Na2SO4 (aq)

b) KOH is soluble in the reaction medium and hence, the solution contains K+.

c) Fe3+ is precipitated in the form of Fe(OH)3.

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