For preparing a set of standard solutions of FeNCS2+, the equilibrium molar concentration of FeNCS2+ is assumed to equal the initial molar concentration of the (SCN-) in the reaction mixture. why is this assumption valid?
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This assumption is valid in the case of preparing a set of standard solutions of FeNCS2+ because FeNCS2+ is formed from the reaction between Fe3+ and SCN-. It is an equilibrium reaction, and assuming that the equilibrium molar concentration of FeNCS2+ equals the initial molar concentration of SCN- is based on the stoichiometry of the reaction.
The balanced chemical equation for the reaction is:
Fe3+ + SCN- ⇌ FeNCS2+
In the reaction, Fe3+ reacts with SCN- to form FeNCS2+. At equilibrium, the rate of the forward reaction (formation of FeNCS2+) will be equal to the rate of the reverse reaction (dissociation of FeNCS2+). This means that the concentration of FeNCS2+ will reach a constant value when the reaction reaches equilibrium.
By assuming that the equilibrium molar concentration of FeNCS2+ is equal to the initial molar concentration of SCN-, it is implied that the reaction has reached equilibrium, and the forward and reverse reactions have balanced each other out. This assumption simplifies the calculation of the equilibrium molar concentration of FeNCS2+ and allows for the preparation of standard solutions with known concentrations.
The assumption that the equilibrium molar concentration of FeNCS2+ is equal to the initial molar concentration of SCN- in the reaction mixture is based on the stoichiometry of the reaction. In order to understand why this assumption is valid, let's first look at the balanced chemical equation for the formation of FeNCS2+:
Fe3+ + NCS- ⇌ FeNCS2+
In this reaction, Fe3+ reacts with NCS- to form FeNCS2+. The stoichiometry of the reaction indicates that for every one Fe3+ ion, one FeNCS2+ ion is produced. Similarly, for every one NCS- ion, one FeNCS2+ ion is produced.
Now, let's consider the reaction conditions for preparing a set of standard solutions of FeNCS2+. These solutions are typically prepared by mixing a known concentration of Fe3+ and a known concentration of SCN-. The reaction mixture is allowed to reach equilibrium, and then the concentration of FeNCS2+ is measured.
Since the reaction has reached equilibrium, the concentrations of all the species involved in the reaction become constant. Therefore, the equilibrium molar concentration of FeNCS2+ can be assumed to be equal to the initial concentration of SCN-, based on the stoichiometry of the reaction.
This assumption is valid because at equilibrium, the rate of the forward reaction (formation of FeNCS2+) equals the rate of the backward reaction (reconversion of FeNCS2+ back to Fe3+ and SCN-). As a result, the reaction has reached a balance, and the concentrations of the reactants and products have stabilized.
It is important to note that this assumption holds only under certain conditions, such as when the reaction between Fe3+ and SCN- is in a well-defined equilibrium state. Additionally, other factors, such as temperature and pH, can also influence the equilibrium concentrations. Therefore, it is crucial to carefully control the reaction conditions in order to ensure the validity of this assumption.