The most common constituents of alkalinity in natural water are measur...
Alkalinity is defined as the number of ions in water that will react to hydrogen ion or it is the ability to neutralize acids.
Source:
Measurement:
- By titrating the water sample with 0.02 N H2SO4 using Phenolphthalein and Methyl Orange indicators.
- The relative quantity of alkalinity species is pH-dependent.
- Expressed in terms of mg/l as CaCO3.
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The most common constituents of alkalinity in natural water are measur...
Explanation:
Titration Process:
- The titration process involves adding a measured amount of 0.02 N H2SO4 to the water sample until the endpoint is reached.
Indicators used:
- In this titration, both phenolphthalein and methyl orange indicators are commonly used.
- Phenolphthalein is used to determine the endpoint for the alkalinity caused by hydroxide, carbonate, and bicarbonate ions.
- Methyl orange is used to detect the endpoint for the total alkalinity in the water sample.
Role of Indicators:
- Phenolphthalein changes color from pink to colorless at a pH of around 8.3-10, indicating the endpoint for hydroxide, carbonate, and bicarbonate ions.
- Methyl orange changes color from red to yellow at a pH of around 4.4-6.3, indicating the endpoint for total alkalinity.
Choice of Indicators:
- The combination of phenolphthalein and methyl orange ensures accurate determination of the different constituents of alkalinity present in the water sample.
- Using these indicators helps in identifying the endpoint for specific ions present in the water, leading to precise alkalinity measurements.
Therefore, the correct choice for measuring the constituents of alkalinity in natural water by titration with 0.02 N H2SO4 is option 'A' - Phenolphthalein and methyl orange indicators.