THEORY EXPERIMENT 4 DETERMINATION OF AN EQUILIBRIUM CONSTANT BY OBJECTIVES (1.) To gain experience with the important method of visible spectrophotometry; and (2.) use this technique to determine the equilibrium constant for the formation of the complex FeSSA(aq) from Fe³+(aq) and H₂SSA (aq). All chemical reactions move spontaneously towards an equilibrium state when the reactants are mixed in arbitrary concentrations. The equilibrium state for a given temperature and pressure is reached when the concentrations of reactants and products are no longer changing. However, when the system approaches and then attains the equilibrium state, there are two opposite processes taking place: the reactant molecules are reacting to form products, and the product molecules are reacting in the reverse direction to form reactant molecules. At the final equilibrium state, the forward and reverse reactions are taking place at the same rate, so that there is no net change in the concentrations of the products and reactants. Mathematically, when the system reaches equilibrium, the product of the molarities of the products raised to their stoichiometric coefficients divided by the product of the molarities of the reactants raised to their stoichiometric coefficients is equal to a constant, called the equilibrium constant, Keq,. As a general example, consider the reaction: aA(aq) +bB(aq) cC(aq) + dD(aq) Q- SPECTROPHOTOMETRY where A (aq) and B(aq) are reactants, C(aq) and D(aq) are product species, and a,b,c, and d are their respective stoichiometric coefficients in the balanced equation. Away from equilibrium, the reaction quotient Q is defined as: [C][D]* [A][B] = [C], [D] [A][B] (1) where the brackets represent the molarity of a species. As the system approaches equilibrium, Q→Keq, and at equilibrium Q=Keq, Ka (2) where the subscripts eq signify the final equilibrium molarities of each species. Keq has a fixed value for any given temperature and pressure, but is independent of the molarity of the species present at equilibrium.

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Using the image attached please write 1 paragraph 1 paragraph: objective stated clearly Please write it in one paragraph only Please please please answer everything it's very important please answer fast Please write it in one paragraph please
THEORY
OBJECTIVES
(1.) To gain experience with the important method of visible spectrophotometry; and
(2.) use this technique to determine the equilibrium constant for the formation of the
complex FeSSA(aq) from Fe³+(aq) and H₂SSA (aq).
EXPERIMENT 4
DETERMINATION OF AN EQUILIBRIUM CONSTANT BY
All chemical reactions move spontaneously towards an equilibrium state when the
reactants are mixed in arbitrary concentrations. The equilibrium state for a given
temperature and pressure is reached when the concentrations of reactants and products
are no longer changing. However, when the system approaches and then attains the
equilibrium state, there are two opposite processes taking place: the reactant molecules
are reacting to form products, and the product molecules are reacting in the reverse
direction to form reactant molecules. At the final equilibrium state, the forward and
reverse reactions are taking place at the same rate, so that there is no net change in the
concentrations of the products and reactants. Mathematically, when the system reaches
equilibrium, the product of the molarities of the products raised to their stoichiometric
coefficients divided by the product of the molarities of the reactants raised to their
stoichiometric coefficients is equal to a constant, called the equilibrium constant, Keq,.
As a general example, consider the reaction:
aA(aq) +bB(aq) cC(aq) + dD(aq)
Q-
SPECTROPHOTOMETRY
where A (aq) and B(aq) are reactants, C(aq) and D(aq) are product species, and a,b,c, and
d are their respective stoichiometric coefficients in the balanced equation. Away from
equilibrium, the reaction quotient Q is defined as:
[C][D]*
[A][B]
K
=
[C], [D]
[A] [B]
where the brackets represent the molarity of a species. As the system approaches
equilibrium, Q→Keq, and at equilibrium Q=Keq,
(1)
(2)
where the subscripts eq signify the final equilibrium molarities of each species. Keq has a
fixed value for any given temperature and pressure, but is independent of the molarity of
the species present at equilibrium.
Transcribed Image Text:THEORY OBJECTIVES (1.) To gain experience with the important method of visible spectrophotometry; and (2.) use this technique to determine the equilibrium constant for the formation of the complex FeSSA(aq) from Fe³+(aq) and H₂SSA (aq). EXPERIMENT 4 DETERMINATION OF AN EQUILIBRIUM CONSTANT BY All chemical reactions move spontaneously towards an equilibrium state when the reactants are mixed in arbitrary concentrations. The equilibrium state for a given temperature and pressure is reached when the concentrations of reactants and products are no longer changing. However, when the system approaches and then attains the equilibrium state, there are two opposite processes taking place: the reactant molecules are reacting to form products, and the product molecules are reacting in the reverse direction to form reactant molecules. At the final equilibrium state, the forward and reverse reactions are taking place at the same rate, so that there is no net change in the concentrations of the products and reactants. Mathematically, when the system reaches equilibrium, the product of the molarities of the products raised to their stoichiometric coefficients divided by the product of the molarities of the reactants raised to their stoichiometric coefficients is equal to a constant, called the equilibrium constant, Keq,. As a general example, consider the reaction: aA(aq) +bB(aq) cC(aq) + dD(aq) Q- SPECTROPHOTOMETRY where A (aq) and B(aq) are reactants, C(aq) and D(aq) are product species, and a,b,c, and d are their respective stoichiometric coefficients in the balanced equation. Away from equilibrium, the reaction quotient Q is defined as: [C][D]* [A][B] K = [C], [D] [A] [B] where the brackets represent the molarity of a species. As the system approaches equilibrium, Q→Keq, and at equilibrium Q=Keq, (1) (2) where the subscripts eq signify the final equilibrium molarities of each species. Keq has a fixed value for any given temperature and pressure, but is independent of the molarity of the species present at equilibrium.
METHOD
Your goal is to determine the equilibrium constant for reaction (4). In order to determine
Keq experimentally, we must find the equilibrium molarities of each of the species
[Fe]eq, [H₂SSA ]eq, and [FeSSA]eq from solution mixtures that you will prepare as
described below. The Hydrogen ion concentration [H*]eq may be assumed to remain
constant since its concentration is much higher than the other species present at
equilibrium, and therefore is omitted from the Keq expression. In your lab notebook
abstract, you should write out the equilibrium constant expression Keq for this reaction.
The product FeSSA, absorbs visible light, while all other species present are essentially
colorless. We can therefore determine the equilibrium molarity of the product species
FeSSA by measuring its absorbance at an appropriate wavelength and using Beer's Law,
as explained below. The equilibrium molarities of the other species will be determined
by using a reaction table, as you have done in homework problems and in class.
Beer's Law. Beer's law is an empirical law stating that the concentration C (in moles per
liter) of a chemical species in solution is directly proportional to its absorbance A:
AxC
with the proportionality constant being a product of the pathlength 7 and the molar
absorptivity (a measure of how strongly the solution absorbs light of a given
wavelength)
A - EIC
For our experiments, 1 is fixed at 1.0 cm. Thus, a graph of the molarities vs. the
absorbances of various solutions (at a fixed appropriate wavelength) will yield a straight
line, the slope of which may be determined either manually (by calculating from
Ax
measured x and y values) or using a computer program such as Excel TM. Once the slope
is known, molarities of unknown solutions may be calculated from their measured
absorbance values. You should be familiar with this method, as it was employed in
chem. 1A.
Transcribed Image Text:METHOD Your goal is to determine the equilibrium constant for reaction (4). In order to determine Keq experimentally, we must find the equilibrium molarities of each of the species [Fe]eq, [H₂SSA ]eq, and [FeSSA]eq from solution mixtures that you will prepare as described below. The Hydrogen ion concentration [H*]eq may be assumed to remain constant since its concentration is much higher than the other species present at equilibrium, and therefore is omitted from the Keq expression. In your lab notebook abstract, you should write out the equilibrium constant expression Keq for this reaction. The product FeSSA, absorbs visible light, while all other species present are essentially colorless. We can therefore determine the equilibrium molarity of the product species FeSSA by measuring its absorbance at an appropriate wavelength and using Beer's Law, as explained below. The equilibrium molarities of the other species will be determined by using a reaction table, as you have done in homework problems and in class. Beer's Law. Beer's law is an empirical law stating that the concentration C (in moles per liter) of a chemical species in solution is directly proportional to its absorbance A: AxC with the proportionality constant being a product of the pathlength 7 and the molar absorptivity (a measure of how strongly the solution absorbs light of a given wavelength) A - EIC For our experiments, 1 is fixed at 1.0 cm. Thus, a graph of the molarities vs. the absorbances of various solutions (at a fixed appropriate wavelength) will yield a straight line, the slope of which may be determined either manually (by calculating from Ax measured x and y values) or using a computer program such as Excel TM. Once the slope is known, molarities of unknown solutions may be calculated from their measured absorbance values. You should be familiar with this method, as it was employed in chem. 1A.
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