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What is Permanent Hardness of Water (non-removable hardness)?
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 hardness caused by dissolved salts of magnesium and calcium, specifically sulfates and chlorides. Unlike temporary hardness, it cannot be removed simply by boiling the water. This is why it's also called non-removable hardness.
Simple Example
Quick Example
Imagine you are trying to wash your clothes, but no matter how much soap you use, you don't get much lather or foam. This could be because your tap water has permanent hardness. The minerals in the water react with the soap, making it less effective, just like how a weak phone signal makes it hard to download a movie.
Worked Example
Step-by-Step
Let's say a water sample contains magnesium sulfate (MgSO4) and calcium chloride (CaCl2). These are the main culprits for permanent hardness.
Step 1: Take 1 liter of this hard water.
---Step 2: Try boiling it for 10-15 minutes. Observe if any white deposits form at the bottom of the vessel.
---Step 3: After boiling, let it cool and then try to wash your hands with soap using this water.
---Step 4: You will notice that even after boiling, the water still forms very little lather with soap. This shows that the hardness (caused by MgSO4 and CaCl2) has not been removed by boiling.
---Answer: The water still exhibits permanent hardness because the dissolved magnesium sulfate and calcium chloride remain in the water after boiling.
Why It Matters
Understanding water hardness is crucial for engineers designing water treatment plants and for scientists working on sustainable water solutions. It's also important in industries like textiles and food processing, and even for maintaining efficient home appliances. This knowledge can lead to careers in environmental science or chemical engineering.
Common Mistakes
MISTAKE: Thinking all hard water can be softened by boiling. | CORRECTION: Only temporary hardness can be removed by boiling. Permanent hardness requires other methods.
MISTAKE: Confusing permanent hardness with temporary hardness. | CORRECTION: Permanent hardness is due to sulfates and chlorides of calcium and magnesium, while temporary hardness is due to bicarbonates of calcium and magnesium.
MISTAKE: Believing permanent hard water is unhealthy to drink. | CORRECTION: While it can cause scale in pipes and less lather with soap, permanently hard water is generally safe to drink and can even provide essential minerals.
Practice Questions
Try It Yourself
QUESTION: Can boiling remove permanent hardness from water? | ANSWER: No, boiling cannot remove permanent hardness.
QUESTION: Name two salts that cause permanent hardness in water. | ANSWER: Magnesium sulfate (MgSO4) and Calcium chloride (CaCl2).
QUESTION: Your washing machine is showing white, chalky deposits inside the pipes, and your clothes don't feel clean even after using extra detergent. Which type of water hardness is most likely causing this problem, and why? | ANSWER: Permanent hardness is most likely causing this problem. This is because the salts causing permanent hardness (like calcium sulfate) do not precipitate out upon boiling (or normal washing temperatures) and build up as scale. They also react with soap/detergent, reducing its effectiveness and making clothes less clean.
MCQ
Quick Quiz
Which of these salts primarily causes permanent hardness in water?
Calcium bicarbonate
Magnesium sulfate
Sodium chloride
Potassium carbonate
The Correct Answer Is:
B
Magnesium sulfate and calcium chloride are the main causes of permanent hardness. Calcium bicarbonate causes temporary hardness, while sodium chloride is common salt and doesn't cause hardness.
Real World Connection
In the Real World
In many Indian households, especially in cities like Bengaluru or Chennai, people often install water purifiers that use Reverse Osmosis (RO) technology. This RO system is specifically designed to remove dissolved salts, including those causing permanent hardness, to give you cleaner and softer drinking water, which also helps prevent scale buildup in kettles and geysers.
Key Vocabulary
Key Terms
HARDNESS: The presence of dissolved mineral salts in water that prevents soap from lathering easily | CALCIUM SULFATE: A salt (CaSO4) that causes permanent hardness | MAGNESIUM CHLORIDE: A salt (MgCl2) that causes permanent hardness | LATHER: The foam produced by soap when mixed with water | SCALE: Hard, crusty deposits formed by mineral salts in pipes and appliances due to hard water.
What's Next
What to Learn Next
Now that you understand permanent hardness, you should learn about 'Temporary Hardness of Water'. This will help you compare the two types of hardness and understand how each can be removed, giving you a complete picture of water hardness.
