Piece 1 Write a balanced equation for the dissolution of FeCO3(s) in water. Piec
ID: 1020837 • Letter: P
Question
Piece 1 Write a balanced equation for the dissolution of FeCO3(s) in water.
Piece 2 Write a balanced equation for the dissolution of MgCO3(s) in water.
Piece 3: Write a balanced equation for the dissolution of Mg(NO3)2 (s) in water.
Piece 4: Write a balanced equation for the dissolution of Fe(NO3)2 (s) in water.
Piece 5: Write a balanced equation for the dissolution of K2CO3 (s) in water.
Piece 6: If I dissolve Mg(NO3)2, Fe(NO3)2, and K2CO3 in water, what chemical species are present in my beaker?
Piece 7: Given the following Ksp values, which salt is LEAST soluble in water?
Ksp[FeCO3] = 3.07x10-11
Ksp[MgCO3] = 6.82x10-6
Ksp[Mg(NO3)2] = 3.14x104
Ksp[Fe(NO3)2] = 6.28x103
Ksp[K2CO3] = 1.26x105
Piece 8. Consider a 1 L solution that is 2.3×10-2 M in Fe(NO3)2 and 1.5×10-2 M in Mg(NO3)2.
What must the concentration of potassium carbonate be to get the iron ions to start to precipitate?
Piece # 9 Consider a 1 L solution that is 2.3×10-2 M in Fe(NO3)2 and 1.5×10-2 M in Mg(NO3)2.
What must the concentration of potassium carbonate be to get the magnesium ions to start to precipitate?
Piece #10. What minimum concentration of K2CO3 is required to cause the precipitation of the cation that precipitates first?
Puzzle 1. How much of the first cation is still in solution when the second cation begins to precipitate?
Puzzle 2. What is the total mass of K2CO3 that must be added to get the second cation to begin to precipitate? [Hint: Where is all the carbonate going?]
Explanation / Answer
Piece 1 : dissolution of FeCO3
FeCO3(s) <---> Fe2+(aq) + CO3^2-(aq)
Piece 2 : Dissolution of MgCO3
MgCO3(s) <---> Mg2+(aq) + CO3^2-(aq)
Piece 3 : Dissolution of Mg(NO3)2
Mg(NO3)2(s) ---> Mg2+(aq) + 2NO3-(aq)
Piece 4 : Dissolution of Fe(NO3)2
Fe(NO3)2(s) ---> Fe2+(aq) + 2NO3-(aq)
Piece 5 : Dissolution of K2CO3
K2CO3(s) ---> 2K+(aq) + CO3^2-(aq)
CO3^2-(aq) + H2O(l) <==> HCO3-(aq) + OH-(aq)
HCO3-(aq) + H2O(l) <===> H2CO3(aq) + OH-(aq)
Piece 6 : Dissolving the three salts would produce the following ions in solution,
Mg2+, Fe2+, K+, H+, OH-, NO3-, CO3^2-, HCO3-, H2CO3
Piece 7 : Least soluble salt has smallest Ksp value,
that is, FeCO3 is least soluble salt here.
Piece 8 : Concentration of [CO3^2-] (K2CO3) to start Mg precipitation = 6.82 x 10^-6/1.5 x 10^-2 = 4.54 x 10^-4 M
Piece 9 : First FeCO3 would precipitate out of solution
Concentration of [CO3^2-] (K2CO3) to start iron precipitation = 3.07 x 10^-11/2.3 x 10^-2 = 1.33 x 10^-9 M
Puzzle 1 : Concentration of Fe2+ when MgCO3 begins precipitation = 3.07 x 10^-11/4.54 x 10^-4 = 6.76 x 10^-8 M
Percentage of first cation (Fe2+) remaining when Mg2+ begins precipitation = 6.76 x 10^-8 x 100/2.3 x 10^-2 = 0.00029%
Puzzle 2 : Total carbonate (K2CO3) to be added to begin precipitation of second cation (Mg2+) = 4.54 x 10^-4 M x 1 L x 138.205 g/mol = 0.063 g