Podcast
Questions and Answers
Which of the following best explains why hard water prevents soap from lathering effectively?
Which of the following best explains why hard water prevents soap from lathering effectively?
- The high concentration of sodium ions in hard water interferes with soap's chemical structure.
- Hard water has a lower pH, which neutralizes the alkaline components of soap.
- The increased viscosity of hard water inhibits the dispersion of soap molecules.
- Calcium and magnesium ions in hard water react with soap to form insoluble scum. (correct)
Boiling water will effectively remove permanent hardness.
Boiling water will effectively remove permanent hardness.
False (B)
What type of chemical compound causes temporary hardness in water?
What type of chemical compound causes temporary hardness in water?
bicarbonates
In Clark's method, the chemical compound __________, is added to hard water to precipitate out calcium and magnesium ions.
In Clark's method, the chemical compound __________, is added to hard water to precipitate out calcium and magnesium ions.
Which of the following methods utilizes an exchange of ions to soften water?
Which of the following methods utilizes an exchange of ions to soften water?
Washing soda (sodium carbonate) can remove both temporary and permanent hardness from water.
Washing soda (sodium carbonate) can remove both temporary and permanent hardness from water.
What is the chemical formula of washing soda?
What is the chemical formula of washing soda?
Match the method with the type of hardness it primarily addresses:
Match the method with the type of hardness it primarily addresses:
Flashcards
Water Hardness
Water Hardness
Water's resistance to forming lather with soap, caused by calcium and magnesium ions.
Temporary Hardness
Temporary Hardness
Hardness caused by calcium and magnesium bicarbonates.
Boiling Removes Temporary Hardness
Boiling Removes Temporary Hardness
Heating water converts bicarbonates to carbonates, CO2, and water, precipitating out.
Clark's Method
Clark's Method
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Permanent Hardness
Permanent Hardness
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Washing Soda
Washing Soda
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Calgon's Method
Calgon's Method
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Ion Exchange Method
Ion Exchange Method
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Study Notes
Hardness of Water
- Water hardness is indicated when soap does not lather well.
- Calcium and magnesium ions in water cause hardness.
- Soaps contain sodium salts of higher fatty acids that create lather.
- Calcium and magnesium ions react with soap salts to form calcium and magnesium salts.
- Calcium and magnesium salts are insoluble and form scum, reducing lather.
- Calcium and magnesium ions in hard water are present as soluble salts like carbonates, chlorides, or sulfates.
Temporary Hardness
- Temporary hardness results from bicarbonates of calcium and magnesium.
- Boiling water can remove temporary hardness.
- Boiling converts calcium bicarbonate to calcium carbonate, water, and carbon dioxide.
- Magnesium bicarbonate changes to magnesium hydroxide and carbon dioxide when boiled.
- Carbon dioxide escapes, while calcium carbonate and magnesium hydroxide form precipitates.
- Filtration removes the precipitates, eliminating calcium and magnesium ions.
- Clark's method involves adding lime (calcium hydroxide) to hard water.
- Lime reacts with calcium bicarbonate to form calcium carbonate and water.
- Lime reacts with magnesium bicarbonate to form calcium carbonate, magnesium hydroxide, and water.
- The resulting calcium carbonate and magnesium hydroxide precipitate out of the water.
- Filtration removes precipitates, softening the water.
Permanent Hardness
- Permanent hardness leads to hard white coatings inside kettles, showers, and utensils.
- Chlorides and sulfates of calcium and magnesium cause permanent hardness.
- Permanent hardness cannot be removed by boiling.
- Chemical methods such as washing soda, Calgon's method, ion exchange, and synthetic resins can remove permanent hardness.
- Washing soda (sodium carbonate) reacts with calcium and magnesium chloride salts to form corresponding carbonate salts and sodium chloride.
- Washing soda also reacts with calcium and magnesium sulfate salts to form corresponding carbonate salts and sodium sulfate.
- Calcium and magnesium carbonate salts precipitate out and are removed by filtration.
- Calgon's method uses sodium hexametaphosphate.
- Calgon ionizes to give sodium ions and a complex anion.
- The complex anion captures calcium or magnesium ions, removing hardness.
- The ion exchange method uses zeolite (sodium aluminum silicate).
- Zeolite exchanges sodium ions for calcium and magnesium ions, which softens the water.
- Synthetic resins exchange sodium ions for calcium and magnesium ions.
Recap
- Temporary hardness is due to calcium and magnesium bicarbonates and is removed by boiling or Clark's method.
- Permanent hardness is due to calcium and magnesium chlorides and sulfates.
- Permanent hardness is removed by washing soda, Calgon's method, ion exchange, or synthetic resins.
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Description
Understand water hardness, its causes due to calcium and magnesium ions, and how it affects soap lather. Learn about temporary hardness caused by bicarbonates and methods like boiling and Clark's method to remove it.
