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Questions and Answers
What is the purpose of determining alkalinity in a water sample?
What is the purpose of determining alkalinity in a water sample?
The purpose is to assess the presence and concentration of hydroxides, carbonates, and bicarbonates, which contribute to the water's alkalinity.
What indicators are used in the titration process to determine alkalinity?
What indicators are used in the titration process to determine alkalinity?
Phenolphthalein and methyl orange indicators are used in the titration process.
How is the volume of standard HCl used in the titration process denoted in relation to the end points?
How is the volume of standard HCl used in the titration process denoted in relation to the end points?
The volume of HCl used is denoted as (P) for the phenolphthalein end point and (M) for the methyl orange end point.
Explain the chemical reaction that occurs when OH− and HCO3− ions are present in the water sample.
Explain the chemical reaction that occurs when OH− and HCO3− ions are present in the water sample.
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What can be inferred if only the phenolphthalein indicator is used in the titration?
What can be inferred if only the phenolphthalein indicator is used in the titration?
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What indicates the end of titration when both phenolphthalein and methyl orange are used?
What indicates the end of titration when both phenolphthalein and methyl orange are used?
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When both CO32− and HCO3− ions are present, how are the volumes of HCl calculated?
When both CO32− and HCO3− ions are present, how are the volumes of HCl calculated?
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Why is it important to know the values of (P) and (M) in the experiment?
Why is it important to know the values of (P) and (M) in the experiment?
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Study Notes
Experiment No. 1: Determination of Alkalinity
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Objective: Determine the alkalinity of a given water sample.
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Reagents/Chemicals: Standard HCl, Phenolphthalein, Methyl Orange Indicator, Water sample.
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Apparatus: Burette, pipette, conical flask, beaker, measuring flask.
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Theory of Alkalinity: Water alkalinity is primarily due to the presence of hydroxides, carbonates, and bicarbonates. These ions react with acids to form carbonates and bicarbonates. OH- and HCO3- ions cannot coexist as they combine to form carbonates.
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Procedure:
- Titrate the water sample with a standard acid (HCl), using phenolphthalein as an indicator. The endpoint, where the solution changes color, marks the neutralization of hydroxide and conversion to carbonates.
- Add methyl orange to the solution, and continue the titration to the endpoint where the color changes from yellow to brick red.
- Using the volume of HCl at both endpoints, and the known formulas, the various forms of alkalinity can be calculated.
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Calculating Alkalinity:
- Only OH- present: Phenolphthalein indicator used, P ml of HCl is employed.
- Only HCO3- present: Methyl orange indicator used. M ml of HCl is employed.
- Only CO32- present: Both indicators are employed. 2M ml of HCl is required.
- Both OH- and CO32- present: Both indicators used. (P-M) ml for OH- and 2M ml for CO32-.
- Both CO32 and HCO3- present: Both indicators used. 2P ml for CO32- and (M-P) ml for HCO3-.
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Description
This quiz focuses on the first experiment of determining the alkalinity of a water sample. It involves understanding the chemical reactions involved in titration using standard HCl and indicators like phenolphthalein and methyl orange. Test your knowledge on procedures, reagents used, and the theory behind alkalinity.
