5. (12 pts) A solution contains 0.0450 M Ca(NO (aq) and 0.0350 M Fe(NO (aq). You

Question

5. (12 pts) A solution contains 0.0450 M Ca(NO (aq) and 0.0350 M Fe(NO (aq). You would like to separate the iron and calcium ions, and you have access to the following solutions: Na COs (aq) HCl (aq) NaOH (aq) a) Circle the solution you should use to separate the calcium ions and the iron ions. b) Which ion will precipitate first? c) What is the formula of this precipitate? d) What concentration of your reagent is required to begin precipitation? e) What concentration of your reagent will just cause precipitation of the second on? f) How much of the first ion will remain at this concentration? (i.e. how good was your separation?) 1 43 Spring 3018

Explanation / Answer

1. Sodium Carbonate, Na2CO3 may be used to separate Ca(NO3)2 and Fe(NO3)2. The double displacement reactions are as follows:

Ca(NO3)2 (aq) + Na2CO3 (aq) -> CaCO3 (s) + 2NaNO3 (aq)  ;

Fe(NO3)2 (aq) + Na2CO3 (aq) -> FeCO3 (s) + 2NaNO3 (aq) ;

2. Since, Ca has higher reactivity than Fe in the reactivity series, Ca displaces Na from Na2CO3, first and forms CaCO3 (s) precipitate.

3. Formula of the precipitate is CaCO3 (s).

4. Any concentration of Na2CO3 upto a maximum of 0.045 M may be used for precipiation of the first ion (Ca2+) to occur. However, for complete precipitation of the first ion, the concentration of Na2CO3 required is 0.045 M i.e the concentration of Ca(NO3)2 .

5. Any concentration just greater than 0.045 M will begin precipitation of the second ion, Fe2+ of which 0.035M is present.

6. At concentrations greater than 0.045M, none of the first ion Ca2+ will be present i.e. 100% separation.

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