suggest a test to find the hardness of water and explain the procedure
Answers
i) Take 10ml of distilled water and 10ml of hard water (from hand pump) in separate test tubes.
ii) Add a couple of drops of soap solution to both.
iii) Shake the test tubes vigorously for an equal period of time and observe the foam formed.
iv) The test tube containing distilled water shows more foam. This is because the whole of soap is available to form foam.
v) The test tube containing hand-pump water may show a white curdy precipitate. This indicates that water is hard water.
vi) Hard water contains soluble salts of calcium or magnesium. This is because calcium and Magnesium ions form precipitate with soap, thus wasting some of the soap.
Answer:
In this test, the hardness of water is measured in parts per million (ppm) of calcium carbonate equivalent. The higher the ppm, the harder the water. This test can also be used to measure the hardness caused by magnesium ions, by adjusting the calibration and calculation accordingly.
Explanation:
One common test to determine the hardness of water is the titration method using EDTA (ethylenediaminetetraacetic acid) as a chelating agent. Here is a step-by-step procedure for this test:
Materials:
Water sample
EDTA solution
Eriochrome Black T indicator
Calcium standard solution
Procedure:
Take a water sample of known volume, and add a few drops of Eriochrome Black T indicator to it. The indicator will turn the solution blue.
Add the EDTA solution slowly from a burette to the water sample until the blue color changes to wine red. This indicates that all the metal ions in the water sample have been chelated by the EDTA, forming a stable complex. Note the volume of EDTA solution added.
Repeat the titration with a blank solution (water without any metal ions) to determine the amount of EDTA solution required to neutralize the indicator alone.
Use the calcium standard solution to calibrate the EDTA solution. This involves adding a known amount of the calcium standard solution to a water sample, titrating it with the EDTA solution, and recording the volume of EDTA solution required to chelate all the calcium ions. Repeat this step several times to obtain an average value for the volume of EDTA solution required.
Calculate the hardness of the water sample using the formula:
Hardness = [(EDTA volume - blank volume) x calcium concentration x 1000] / water sample volume
In this test, the hardness of water is measured in parts per million (ppm) of calcium carbonate equivalent. The higher the ppm, the harder the water. This test can also be used to measure the hardness caused by magnesium ions, by adjusting the calibration and calculation accordingly.
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