Hard & Soft Water — Homi Bhabha Class 6 Chemistry MCQs with Solutions
Free Homi Bhabha Class 6 Chemistry Hard & Soft Water MCQs with step-by-step solutions (10 questions). Part of Water & Its Management. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Hard & Soft Water · easy · theory
Water that quickly makes a lot of lather (foam) with soap is called …
A. Salty water
B. Hard water
C. Soft water ✓ Correct
D. Muddy water
Solution: Soft water forms a rich lather easily with soap, so it is good for washing. Rainwater is a common example.
Q2 — Hard & Soft Water · easy · theory
Water that does NOT easily form lather with soap is called …
A. Hard water ✓ Correct
B. Distilled water
C. Rainwater
D. Soft water
Solution: Hard water does not lather well because the salts in it react with the soap instead of making foam. So it is called hard water.
Q3 — Hard & Soft Water · easy · theory
Which of these is usually an example of soft water?
A. Sea water
B. Water from a hot spring
C. Well water in a rocky area
D. Rainwater ✓ Correct
Solution: Rainwater has very few dissolved salts because it forms from evaporated water, so it is soft.
Q4 — Hard & Soft Water · easy · theory
The white, sticky, dirty solid formed when soap is used with hard water is called …
A. Foam
B. Cream
C. Scum ✓ Correct
D. Ice
Solution: In hard water the soap joins with the salts to form a white sticky solid called scum, instead of making lather.
Q5 — Hard & Soft Water · medium · theory
Hard water is hard mainly because it contains dissolved salts of …
A. Iron and gold
B. Sugar and salt
C. Calcium and magnesium ✓ Correct
D. Sand and clay
Solution: The hardness of water is caused by dissolved calcium and magnesium salts that it picks up from rocks and soil.
Q6 — Hard & Soft Water · medium · theory
A simple way to make hard water softer at home is to …
A. Shake it well
B. Add more soap to it
C. Boil it ✓ Correct
D. Cool it in a fridge
Solution: Boiling hard water makes some of the dissolved salts separate out and settle, which reduces the hardness of the water.
Q7 — Hard & Soft Water · medium · theory
The hard white layer (scale) left inside a kettle after boiling water many times is caused by …
A. Sugar in the water
B. Soap left in the kettle
C. Dissolved salts in hard water ✓ Correct
D. Rust from the air
Solution: When hard water boils, the dissolved calcium and magnesium salts come out of the water and stick to the kettle as a hard layer called scale.
Q8 — Hard & Soft Water · medium · theory
To wash the same clothes clean, which needs MORE soap?
A. Both need exactly the same
B. Neither needs soap
C. Hard water ✓ Correct
D. Soft water
Solution: Some soap is wasted forming scum in hard water before any lather appears, so hard water needs more soap than soft water.
Q9 — Hard & Soft Water · hard · theory
Why does soap not clean clothes well in hard water?
A. Hard water makes the soap too slippery
B. Hard water turns the soap into oil
C. The soap reacts with the salts to form scum instead of making lather ✓ Correct
D. The soap dissolves completely and disappears
Solution: The calcium and magnesium salts in hard water react with the soap to make a useless scum. Little soap is left to form lather, so cleaning is poor.
Q10 — Hard & Soft Water · hard · theory
Rainwater is soft when it falls, but the water in some wells is hard. How does the water become hard?
A. It gets heated by the Sun underground
B. It dissolves calcium and magnesium salts as it flows through rocks and soil ✓ Correct
C. It freezes and melts many times
D. It mixes with soap in the ground
Solution: As soft rainwater soaks through the ground, it slowly dissolves calcium and magnesium salts from the rocks, and this makes the water hard.