Foundations of Chemistry Laboratory Manual EQUILIBRIUM and LE CHÂTELIER’S PRINCIPLE
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EXPERIMENT 4F
Equilibrium and
Le Châtelier’s Principle (This experiment is done in pairs. Note: you may wish to divide part 1 and 2 between partners.)
Useful background reading (this is not compulsory but may be helpful):
Tro, 4th and 5th Edition: Sections 15.3, 15.7, 15.8, 14.9 (Intro only) – Questions 1 and 2 Sections 12.1 and 12.6 – Question 3
What is the relevance of this prac…?
The prac brings together several concepts that underpin many areas of chemistry study. You will undertake your first laboratory synthesis in which you make a compound (much like cooking but you don’t get to lick the bowl!).
You will then analyse, using Le Châtelier’s Principle, how the reaction conditions may be optimised in order to maximise the amount of product you obtain. Le Châtelier’s Principle can be used to predict outcomes on a small scale such as your reaction vessel, on a miniscule scale such as in cells and on a planetary scale such as in Earth’s atmosphere.
Finally, you will examine how the charge of a species determines what solvents it can be
dissolved in. The type of possible intermolecular forces present between the solute and solvent
will dictate solubility and this is investigated during this practical. Intermolecular forces are
incredibly important and we take them for granted all the time. They are responsible for oxygen
being a gas at room temperature so we can breathe it in and water being a liquid at room
temperature so we can drink it.
Learning objectives (remember these are different to the scientific objectives):
On completion of this practical, you should have:
Become familiar with the class of chemical compounds called “co-ordination complexes”
Understand that a co-ordination complex consists of a metal cation at the centre
surrounded by ligands
Recall the concept of equilibrium from lectures and consider how it relates to this
practical
A BIG Question
What is life?
Life is dependent on many things working
together in concert to give a cohesive whole.
One of the many things on which human life
is dependent is the process of equilibrium.
Equilibrium processes are involved in
controlling the acidity of our blood and the
transport of oxygen in our bodies, among
many other things.
Foundations of Chemistry Laboratory Manual EQUILIBRIUM and LE CHÂTELIER’S PRINCIPLE
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Fe3+ and 6 x O
H H
Become familiar with Le Châtelier’s Principle and use it to predict and explain changes in
the equilibrium position based on a change of reaction conditions
Note: this practical has three parts and can be quite long. However, many of the questions
(including all of those in Part Three) do not rely on experimental results and can be answered
prior to the practical if you have an understanding of equilibrium, Le Châtelier’s Principle and
intermolecular forces. It is possible to thoroughly prepare for this practical before you step into
the lab and students who do this should not find any problems with its length.
Introduction (extra background)
CO-ORDINATION COMPLEXES
This experiment involves the synthesis and investigation of a co-ordination complex:
tris(acetylacetonato) iron (III). Co-ordination complexes are a class of compounds that most
commonly involve a central metal ion which is surrounded by a certain number of molecules or
ions called ligands. These ligands are said to “co-ordinate” to the metal centre and therefore
the bond formed between them is referred to as a co-ordinate bond.
The complex you begin with in solution at the start of your reaction in Part One is made up of
the following species:
Fe3+ is the central metal ion and it is surrounded by six water ligands.
The formula for this complex is displayed like this: [Fe(H2O)6] 3+. This
species is also referred to as the “aquated Fe3+ ion” because it is a
metal cation surrounded by only water ligands. Everything inside the
square brackets is part of the complex – the metal centre and ligands.
The charge outside is that of the overall complex. The complex is also
shown diagrammatically in two ways below:
In diagram (a) we can see the Fe3+ cation at the centre with six positions around it for six water
ligands. Diagram (b) is conventionally how complexes are displayed and corresponds to the
formula: [Fe(H2O)6] 3+. The charge on the overall complex is a result of adding all the charges on
the metal centre and ligands together. The metal in this case has a 3+ charge and all six water
Fe3+
H2O