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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.
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?
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?
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?
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?
Flashcards
What is alkalinity in water?
What is alkalinity in water?
Alkalinity is the water's ability to neutralize acids. It's caused by the presence of hydroxide (OH-), carbonate (CO32-), and bicarbonate (HCO3-) ions.
How are different types of alkalinity determined?
How are different types of alkalinity determined?
Titration with a standard acid, like HCl, is used to determine the amount of alkalinity. Indicators like phenolphthalein and methyl orange help identify the end points of the reaction.
Phenolphthalein end point (P)
Phenolphthalein end point (P)
The point in titration where all hydroxide (OH-) ions are neutralized, and carbonate (CO32-) ions are converted to bicarbonate (HCO3-).
Methyl orange end point (M)
Methyl orange end point (M)
The point in titration where all bicarbonate (HCO3-) ions are neutralized, leaving only carbon dioxide (CO2).
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How to calculate alkalinity for only hydroxide (OH-) ions?
How to calculate alkalinity for only hydroxide (OH-) ions?
The volume of HCl used at the phenolphthalein end point (P) directly represents the amount of hydroxide ions present.
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How to calculate alkalinity for only bicarbonate (HCO3-) ions?
How to calculate alkalinity for only bicarbonate (HCO3-) ions?
The volume of HCl used at the methyl orange end point (M) represents the amount of bicarbonate ions present.
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How to calculate alkalinity for only carbonate (CO32-) ions?
How to calculate alkalinity for only carbonate (CO32-) ions?
The volume of HCl used at the methyl orange end point (M) is doubled to get the amount of carbonate ions present.
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How to calculate alkalinity for a mix of hydroxide (OH-) and carbonate (CO32-) ions?
How to calculate alkalinity for a mix of hydroxide (OH-) and carbonate (CO32-) ions?
The difference between P and M volume represents the amount of OH- ions. The doubled M volume represents CO32- ions.
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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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