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Questions and Answers
What is the mass of disodium EDTA required to prepare 500 mL of a 0.25 M solution?
What is the mass of disodium EDTA required to prepare 500 mL of a 0.25 M solution?
Which indicator is commonly used in direct EDTA titrations for determining the endpoint?
Which indicator is commonly used in direct EDTA titrations for determining the endpoint?
What is the molarity of the EDTA solution if a 200 mg sample of pure calcium carbonate was dissolved in 500 mL and required 25 mL of the EDTA solution for titration?
What is the molarity of the EDTA solution if a 200 mg sample of pure calcium carbonate was dissolved in 500 mL and required 25 mL of the EDTA solution for titration?
In a zinc sulfate titration using EDTA, what is the role of the indicator?
In a zinc sulfate titration using EDTA, what is the role of the indicator?
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What is the purpose of the residual EDTA titration in the analysis of a metal ion?
What is the purpose of the residual EDTA titration in the analysis of a metal ion?
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What is the indicator used in the direct EDTA titration of calcium?
What is the indicator used in the direct EDTA titration of calcium?
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Why is residual EDTA titration applied to the analysis of Al and Bi complexes?
Why is residual EDTA titration applied to the analysis of Al and Bi complexes?
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What is the indicator used in the standardization of disodium EDTA solution?
What is the indicator used in the standardization of disodium EDTA solution?
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Which indicator is specifically used in the titration of Bismuth?
Which indicator is specifically used in the titration of Bismuth?
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What happens at the endpoint in Zinc sulfate titration?
What happens at the endpoint in Zinc sulfate titration?
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How is the displacement of Ca+2 from the EDTA complex achieved in direct EDTA titration?
How is the displacement of Ca+2 from the EDTA complex achieved in direct EDTA titration?
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What is the primary role of EDTA in analytical chemistry?
What is the primary role of EDTA in analytical chemistry?
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Which of the following metal ions form relatively weak or unstable complexes with EDTA?
Which of the following metal ions form relatively weak or unstable complexes with EDTA?
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Why is disodium EDTA preferred over the free acid form for preparing standard EDTA solutions?
Why is disodium EDTA preferred over the free acid form for preparing standard EDTA solutions?
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What is the purpose of masking agents in EDTA titrations?
What is the purpose of masking agents in EDTA titrations?
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Which of the following is a common method for masking aluminum ions in the presence of magnesium ions during EDTA titrations?
Which of the following is a common method for masking aluminum ions in the presence of magnesium ions during EDTA titrations?
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In a residual EDTA titration, what is the purpose of the back-titration step?
In a residual EDTA titration, what is the purpose of the back-titration step?
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Study Notes
Disodium EDTA
- Disodium EDTA (C10H14N2Na2O8·2H2O) is an analytical agent that reacts with metal ions to form a water-soluble, stable complex, or chelate compound.
- It is preferred over the free acid in preparing the standard solution of EDTA since it is more water-soluble, non-hygroscopic, and very stable.
EDTA Formula and Calculations
- The formula to calculate the weight of disodium EDTA required is: wt = M x MW x L
- Example calculation: wt = 0.1M x 372g/mol x 0.5L = 18.6g disodium EDTA
Indicator Used in Direct EDTA Titration
- Indicators used in direct EDTA may be: EBT, Hydroxynaphthol blue, and pyridyl azonaphthol (red with Zn+2 which forms a violet complex)
Titration Methods
- Mercuric-EDTA complex reaction is used as the masking agent in the titration of calcium
- Residual EDTA titration is applied to the analysis of Al and Bi complex
- In the case of Zinc sulfate titration, a sensitive indicator is used to the titrant, and the metal being determined remains complexed with EDTA and does not interfere with Zn-EDTA complexation
- Bismuth titration forms a highly stable complex that can be titrated at a pH as low as 1 or 2, with dithizone as the indicator
Masking
- Masking is the term used to indicate the determination of a metal in the presence of another metal
- The masking agent is capable of entering into a complication reaction which is accomplished by:
- Adjusting the pH of the titration medium so that it will be favorable for the complexation of the metal that is being determined and not the other metal
- Using an auxiliary complexing agent such as Triethanolamine (TEA)
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Description
Learn about indicators used in direct EDTA titration including EBT, Hydroxynaphthol blue, and pyridyl azonaphthol. Understand the process of calcium assay with Mercuric-EDTA complex reaction and the use of standard mercuric nitrate as a titrant.
