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Chapter 17: Problem 18

A solution was prepared by dissolving about \(3.0 \mathrm{~g}\) of \(\mathrm{NaH}_{2} \mathrm{Y}_{2} \cdot 2 \mathrm{H}_{2} \mathrm{O}\) in approximately \(1 \mathrm{~L}\) of water and standardizing against \(50.00-\mathrm{mL}\) aliquots of \(0.004423 \mathrm{M}\) \(\mathrm{Mg}^{2+}\). An average titration of \(30.27 \mathrm{~mL}\) was required. Calculate the molar concentration of the EDTA.

Short Answer

Expert verified
The molarity of the EDTA solution is approximately 0.00731 M.

Step by step solution

01

Calculate Moles of Mg虏鈦�

First, calculate the moles of Mg虏鈦� in the 50 mL aliquot using its molarity. Use the formula: \[ \text{moles of Mg}^{2+} = \text{Volume (L)} \times \text{Molarity (mol/L)} \] Given that the volume is 50 mL, convert it to liters: \( 50\, \text{mL} \times \frac{1 \text{ L}}{1000 \text{ mL}} = 0.050 \text{ L} \). Now, calculate the moles of Mg虏鈦�: \[ 0.050 \text{ L} \times 0.004423 \text{ mol/L} = 0.00022115 \text{ mol Mg}^{2+}\].
02

Determine Moles of EDTA Used

Assuming a 1:1 molar ratio between Mg虏鈦� and EDTA, the moles of EDTA used are also \(0.00022115\) mol, as per the reaction \( \text{Mg}^{2+} + \text{EDTA}^{4-} \rightarrow \text{Mg-EDTA} \).
03

Calculate Molarity of EDTA Solution

To find the molarity of EDTA, use the volume of EDTA solution used in the titration. The formula to use is: \[ \text{Molarity of EDTA} = \frac{\text{moles of EDTA}}{\text{volume of EDTA solution in L}} \] The volume given is 30.27 mL, which is \( 0.03027 \text{ L} \). Thus, \[ \text{Molarity of EDTA} = \frac{0.00022115}{0.03027} \approx 0.00731 \text{ M} \].

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Solution Standardization
Standardizing a solution is essentially about determining its exact concentration. This process is crucial when the solution is used as a titrant, as it ensures accurate and precise measurements throughout experiments. In the context of the EDTA titration, standardizing involves using a solution with a known concentration, called a standard solution, to titrate the EDTA solution whose concentration is unknown.
The standard solution used here is a 0.004423 M solution of Mg虏鈦�. By titrating 50.00 mL of this solution against the EDTA, we can determine how much EDTA is needed to exactly react with the known amount of Mg虏鈦� ions. Such standardization steps are vital for consistency and credibility. They ensure that any subsequent measurements using the EDTA solution are accurate.
  • The known solution helps check and adjust the concentration of the unknown solution.
  • Standardization often involves stoichiometric reactions that are well-characterized as is the case with titrations.
  • Accurate recording of volumes and complete reaction are imperative for precise standardization.
Molar Concentration Calculation
Molar concentration, also known as molarity, is key in understanding how much solute is in a given volume of solution. In this case, it helps us find out how concentrated the EDTA solution is after standardization.
To calculate the molarity of EDTA, we rely on the moles of the reacted component, which in this exercise was the Mg虏鈦�. By finding the moles of Mg虏鈦� from its volume and molarity, we can equate this to the moles of EDTA used since they react in a 1:1 molar ratio. From there, the molarity is calculated by dividing the number of moles of EDTA by the volume of EDTA solution used.
  • Molarity (\(M\)) is expressed in moles per liter (mol/L).
  • Moles are calculated by multiplying the volume (converted to liters) by the molarity.
  • The precise measurement of volume is necessary for accurate molarity calculations.
Metal-Ligand Complexation
Metal-ligand complexation plays a central role in EDTA titration. This process involves the formation of a complex between a metal ion, like Mg虏鈦�, and a ligand, such as EDTA. This complexation is what allows the titration to progress and reach a clear endpoint.
In these titrations, EDTA acts as a chelating agent that binds to the metal ion, forming a stable complex. The metal-EDTA complex is less reactive, resulting in dramatic changes that signal the endpoint of a titration.
Understanding metal-ligand complexation in this context helps comprehend how and why certain titrations are effective:
  • EDTA forms typically 1:1 complexes with metal ions, which simplifies stoichiometry.
  • The complex formed is stable, which means it significantly lowers free metal ion concentration.
  • Complexation can be visually observed by sudden color changes through indicators, marking titration endpoints clearly.

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Most popular questions from this chapter

The Tl in a 9.57-g sample of rodenticide was oxidized to the trivalent state and treated with an unmeasured excess of \(\mathrm{Mg} / \mathrm{EDTA}\) solution. The reaction is $$ \mathrm{Tl}^{3+}+\mathrm{MgY}^{2-} \rightarrow \mathrm{TlY}^{-}+\mathrm{Mg}^{2+} $$ Titration of the liberated \(\mathrm{Mg}^{2+}\) required \(12.77 \mathrm{~mL}\) of \(0.03610 \mathrm{M}\) EDTA. Calculate the percent \(\mathrm{Tl}_{2} \mathrm{SO}_{4}\) \((504.8 \mathrm{~g} / \mathrm{mol})\) in the sample.

Calamine, which is used for relief of skin irritations, is a mixture of zinc and iron oxides. A 1.056-g sample of dried calamine was dissolved in acid and diluted to \(250.0 \mathrm{~mL}\). Potassium fluoride was added to a \(10.00-\mathrm{mL}\) aliquot of the diluted solution to mask the iron; after suitable adjustment of the \(\mathrm{pH}, \mathrm{Zn}^{2+}\) consumed \(38.37 \mathrm{~mL}\) of \(0.01133 \mathrm{M}\) EDTA. A second \(50.00-\mathrm{mL}\) aliquot was suitably buffered and titrated with \(2.30\) \(\mathrm{mL}\) of \(0.002647 \mathrm{M} \mathrm{ZnY}^{2-}\) solution: $$ \mathrm{Fe}^{3+}+\mathrm{ZnY}^{2-} \rightarrow \mathrm{FeY}^{-}+\mathrm{Zn}^{2+} $$ Calculate the percentages of \(\mathrm{ZnO}\) and \(\mathrm{Fe}_{2} \mathrm{O}_{3}\) in the sample.

Why are multidentate ligands preferable to unidentate ligands for complexometric titrations?

A 0.6004-g sample of \(\mathrm{Ni} / \mathrm{Cu}\) condenser tubing was dissolved in acid and diluted to \(100.0 \mathrm{~mL}\) in a volumetric flask. Titration of both cations in a \(25.00-\mathrm{mL}\) aliquot of this solution required \(45.81\) \(\mathrm{mL}\) of \(0.05285 \mathrm{M}\) EDTA. Mercaptoacetic acid and \(\mathrm{NH}_{3}\) were then introduced; production of the Cu complex with the former resulted in the release of an equivalent amount of EDTA, which required a \(22.85-\mathrm{mL}\) titration with \(0.07238 \mathrm{M} \mathrm{Mg}^{2+}\). Calculate the percent \(\mathrm{Cu}\) and \(\mathrm{Ni}\) in the alloy.

Describe three general methods for performing EDTA titrations. What are the advantages of each?
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