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What is Permanent Hardness of Water?
Grade Level:
Class 6
Space Technology, EVs, Climate Change, Biotechnology, HealthTech, Robotics, Chemistry, Physics
Definition
What is it?
Permanent hardness of water is a type of water hardness that cannot be removed simply by boiling. It is caused by the presence of dissolved mineral salts like calcium sulphate and magnesium sulphate in the water.
Simple Example
Quick Example
Imagine you're trying to make tea, but no matter how much you boil the water, you still see a lot of 'salt' marks left inside the kettle or on your tea glass after it dries. This means your tap water likely has permanent hardness, as boiling alone doesn't get rid of those mineral deposits.
Worked Example
Step-by-Step
Let's say you have 100 ml of hard water containing 50 mg of calcium sulphate.
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Step 1: You try to boil this water for 10 minutes.
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Step 2: After boiling, you cool the water and observe. You notice that the 50 mg of calcium sulphate is still dissolved in the water, and no solid particles have settled down.
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Step 3: This shows that boiling did not remove the calcium sulphate.
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Result: The water exhibits permanent hardness because the dissolved minerals causing it were not removed by boiling.
Why It Matters
Understanding permanent hardness is crucial in industries like HealthTech, ensuring safe drinking water, and Chemistry, for water treatment. It's also vital in designing efficient systems for Space Technology and EVs, where mineral deposits can damage equipment. Engineers and environmental scientists often work with this concept.
Common Mistakes
MISTAKE: Thinking all hard water can be made soft by boiling. | CORRECTION: Only temporary hardness can be removed by boiling; permanent hardness requires other methods.
MISTAKE: Confusing the causes of temporary and permanent hardness. | CORRECTION: Temporary hardness is due to bicarbonates, while permanent hardness is due to sulphates and chlorides of calcium and magnesium.
MISTAKE: Believing permanent hardness is always visible as a cloudy appearance. | CORRECTION: Permanent hardness comes from dissolved salts, so the water might look clear, but still be hard.
Practice Questions
Try It Yourself
QUESTION: Can boiling remove permanent hardness from water? | ANSWER: No, boiling cannot remove permanent hardness from water.
QUESTION: Name two mineral salts that cause permanent hardness in water. | ANSWER: Calcium sulphate and Magnesium sulphate.
QUESTION: Your grandmother complains that her new electric kettle is getting white deposits even though she boils water daily. What type of hardness is likely present in her tap water, and why is boiling not helping? | ANSWER: Permanent hardness is likely present. Boiling only removes temporary hardness (bicarbonates); the sulphates and chlorides causing permanent hardness remain dissolved even after boiling.
MCQ
Quick Quiz
Which of these salts is a common cause of permanent hardness in water?
Calcium bicarbonate
Magnesium chloride
Sodium chloride
Potassium carbonate
The Correct Answer Is:
B
Magnesium chloride is a salt that causes permanent hardness. Calcium bicarbonate causes temporary hardness, while sodium chloride and potassium carbonate do not cause water hardness.
Real World Connection
In the Real World
In many Indian homes, especially in areas with groundwater, people use water purifiers with RO (Reverse Osmosis) technology. These purifiers are specifically designed to remove dissolved salts like those causing permanent hardness, ensuring the water is safe and doesn't damage appliances like geysers and washing machines.
Key Vocabulary
Key Terms
HARDNESS: The presence of dissolved minerals in water | SULPHATES: A type of chemical salt, like calcium sulphate, causing permanent hardness | CHLORIDES: Another type of chemical salt, like magnesium chloride, causing permanent hardness | DISSOLVED: When a substance mixes completely into a liquid to form a solution
What's Next
What to Learn Next
Now that you understand permanent hardness, you can explore 'How to remove permanent hardness of water?'. This will teach you the different methods used to treat hard water, which is a very useful application of this concept!
