SSC
Water that does not form lather (foam) easily with soap is called:
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Answer: Option A — Hard water
Detailed Solution
Hard water contains dissolved salts of calcium and magnesium, mainly their bicarbonates, chlorides and sulphates. Water picks up these salts as it flows over and through rocks such as limestone and dolomite. When soap is added to hard water, the calcium and magnesium ions react with the soap to form an insoluble, sticky substance called scum. Much of the soap is wasted in forming scum, so it does not lather easily, and clothes are not cleaned properly.
Water that lathers easily with soap is called soft water. Rain water and distilled water are soft.
Hardness is of two types:
Temporary hardness is caused by the bicarbonates of calcium and magnesium. It can be removed simply by boiling, which changes the bicarbonates into insoluble carbonates that settle down, or by Clark's method, adding a calculated amount of lime (calcium hydroxide).
Permanent hardness is caused by the chlorides and sulphates of calcium and magnesium. It cannot be removed by boiling. It is removed by adding washing soda (sodium carbonate), by the ion-exchange (permutit or zeolite) method, or by using ion-exchange resins and reverse osmosis.
Hard water causes scaling (deposits) in kettles, boilers and pipes, which wastes fuel and can cause boilers to burst. Detergents, unlike soaps, work well in hard water, because their calcium and magnesium salts are soluble. Hardness is measured in parts per million (ppm) of calcium carbonate equivalent.
Why not the other options?
- ✗Soft water forms lather easily with soap.
- ✗Heavy water (D2O) contains deuterium and is used in nuclear reactors as a moderator.
- ✗Distilled water is pure water without dissolved salts, so it lathers easily.
Quick tip
Remember: Hard water = calcium and magnesium salts; temporary hardness (bicarbonates) removed by boiling; permanent hardness (chlorides, sulphates) by washing soda or ion exchange.
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Chemistry in Everyday Life — Preparation
This question tests your understanding of Chemistry in Everyday Life, a key topic in the General Knowledge section. The detailed solution above uses a step-by-step approach to show the reasoning, and where available, a shortcut that helps you solve similar questions in under 90 seconds during the actual exam.
This topic covers chemistry in daily life: fuels and their calorific values, fertilisers, cement and glass, medicines such as antibiotics and analgesics, food preservatives and additives, cleaning agents, fire extinguishers, and the chemistry of the environment. Questions usually ask about the main component of a fuel (LPG is mainly butane and propane, and CNG is mainly methane), which gas is used in fire extinguishers (carbon dioxide), and what a medicine or chemical is used for. Read the explanation for each question carefully, since one fact is often tested in several ways. Practise the chemistry in everyday life questions below, written in the style of the general awareness sections of exams such as SSC, banking, railways, CUET GAT, MAH CET and CLAT. Each question comes with a detailed explanation that adds related facts, so every question helps you revise more than one point.