Chemistry: Equilibrium and LeChatelier's principle
These are practical questions to be done in lab, for writing a solution/calculation with no values/experimental results please make an educated guess because the prac is yet to be done.
Question 1
a) Write down the overall equation showing the formation of [Fe(acac)3] from [Fe(H2O)6]3+ and acetylacetone [Fe(H2O)6] 3+ (aq) + 3(acac)H(aq) [Fe(acac)3](aq) + 6H2O(l) +3H+ (aq).
b) What reagent (chemical agent) do you weigh out that ends up being the source of the [Fe(H2O)6]3+?
Question 2
a) Circle the correct word in bold text to complete the following statements: A pH of less than 7 means a solution is acidic/basic. A pH of greater than 7 means a solution is acidic/basic.
b) The equation showing acetylacetone, acacH, forming the acac¯ ion is below:
acacH => acac¯ + H+
What is it about this equation that results in a solution of acacH being slightly acidic?
c) Given that sodium acetate is a base (remember that sodium acetate can be considered as sodium ions and acetate ions), complete the following equation showing the reaction of acetate ions with H+ :
CH3COO- + H+ => _________
Question 3
a) What is the connection between the two equations below?
acacH => acac¯ + H+
[Fe(H2O)6] 3+ + acac¯ => [Fe(H2O)4(acac)]2+ + 2H2O
b) Using your answer to Question 3(a), explain why the pH of a mixture of [Fe(H2O)6] 3+ and acacH is lower than a solution of either of the components by themselves.
c) Explain why the pH increases on addition of sodium acetate.
d) Therefore, explain why more [Fe(acac)3] is produced after the addition of sodium acetate. (Hint: use the Equation [Fe(H2O)6] 3+(aq) + 3acacH(aq) [Fe(acac)3](aq) + 6H2O(l) +3H+ (aq) and Le Châtelier's Principle.) (refer to the document for the principle).
Question 4: [Pg 11 on the document, also need to scroll back to Part 1 to answer this]
a) Steps 1 and 2 in the PROCEDURE describe test tubes A and B in Diagram 1. Test tube A should contain the neutral [Fe(acac)3] complex synthesised in Part One and polar water, test tube B should contain [Fe(acac)3] and non-polar dichloromethane. Using the idea of "like dissolves like", which test tube - A or B - do you predict will contain the dissolved [Fe(acac)3]? (Hint: see the notes on solubility in the Introduction section for help.)
b) If the intensity of the colour of the solutions can be taken as a rough guide as to the concentration, which solvent layer in test tube B, the top or the bottom, contains the most [Fe(acac)3]?
c) Is the layer you chose in question 4 (b) the polar (water) layer or the non-polar (dichloromethane) layer?
Question 5
a) Complete the equations that describe the stepwise formation of the tris-acac iron complex, [Fe(acac)3]:
1) [Fe(H2O)6] 3+ + acac¯ => [Fe(H2O)4(acac)]2+ + 2H2O
2) _________________ => ______________________
3) _________________ => [Fe(acac)3] + 2H2O
b) In Question 5(a) you have written the stepwise equilibrium reactions that must occur in order to produce the final complex, [Fe(acac)3]. All three equilibria can be occurring in solution to differing extents depending on what species are present and how Le Châtelier's Principle might affect the reaction position. The three test tubes in Diagram 2 (steps 3, 4 and 5 in the PROCEDURE) show varying extents of reaction. Of the four complexes present in the reaction scheme, which solvent would you expect each one to be soluble in: polar water or non-polar dichloromethane? (First answer is provided.)
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Complex
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Solubility
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Water
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Dichloromethane
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[Fe (H2O)6]3+
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Yes
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No
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[Fe (H2O)4(acac)]2+
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[Fe (H2O)2(acac)2]1+
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[Fe (acac)3]
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Question 6:
If the colour intensity of the layers changes position on going from test tube 2 to test tube 3, what does this suggest about the complexes that are present and, therefore, what has happened to the equilibrium position?