Why is water called the universal solvent?
Water is called the universal solvent because it can dissolve many substances effectively.
What are the natural sources of water?
Natural sources of water include rainwater, well water, spring water, and sea water.
What are the treated sources of water?
Treated sources of water include distilled water, pipe-borne water, and chlorinated water.
What is the difference between soft water and hard water?
Soft water easily forms lather with soap, while hard water does not lather easily due to dissolved salts.
Describe the structure of a water molecule.
A water molecule (H₂O) has oxygen as its central atom with two lone pairs and forms covalent bonds with two hydrogen atoms, resulting in a V-shaped or bent molecular geometry with a bond angle of approximately 105°.
How is water prepared in the laboratory?
Dry hydrogen gas is ignited in air, producing steam. When the steam contacts a cold surface, it condenses to form water.
What are the physical properties of water?
Boiling point: 100°C, Freezing point: 0°C, Maximum density: 1 g/cm³ at 4°C, Neutral to litmus.
How does water react with electropositive metals?
Water reacts with electropositive metals to form alkalis and release hydrogen gas. For example: 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g).
Which metals do not react with water?
Cu, Au, Ag, and Hg do not react with water.
How does water react with non-metals like chlorine?
Water reacts with non-metals like chlorine to form acidic solutions: H₂O(l) + Cl₂(g) → HCl(aq) + HOCl(aq).
What are two laboratory tests for water?
1. Water turns white anhydrous copper(II) tetraoxosulphate(VI) blue. 2. Water turns blue cobalt(II) chloride paper pink.
What is hard water?
Hard water does not easily form lather with soap. It gains hardness from soluble salts such as CaSO₄, MgSO₄, and Ca(HCO₃)₂ present in the soil.
What causes temporary hardness of water?
Temporary hardness is caused by Ca(HCO₃)₂.
What causes permanent hardness of water?
Permanent hardness is caused by CaSO₄, MgSO₄, CaCl₂, and MgCl₂.
How can temporary hardness be removed by boiling?
By boiling: Ca(HCO₃)₂(aq) → CaCO₃(s) + H₂O(l) + CO₂(g).
How can temporary hardness be removed by adding slaked lime?
By adding slaked lime: Ca(HCO₃)₂(aq) + Ca(OH)₂(aq) → 2CaCO₃(s) + 2H₂O(l).
What are the effects of temporary hardness?
Effects of temporary hardness include build-up of fur in kettles and boilers, and formation of stalagmites and stalactites in caves.
How can permanent hardness be removed by adding washing soda?
By adding washing soda: Na₂CO₃(aq) + CaSO₄(aq) → CaCO₃(s) + Na₂SO₄(aq).
How can permanent hardness be removed by adding caustic soda?
By adding caustic soda: 2NaOH(aq) + CaSO₄(aq) → Ca(OH)₂(s) + Na₂SO₄(aq).
How can permanent hardness be removed by ion exchange?
By ion exchange using sodium zeolite: CaSO₄(aq) + Na-zeolite → Ca-zeolite (insoluble) + Na₂SO₄(aq).
What are the advantages of hard water?
Advantages of hard water: it tastes better than soft water, contains calcium salts that strengthen teeth and bones, helps crustaceans build shells, and doesn't dissolve lead, making it safe in lead pipes.
What are the disadvantages of hard water?
Disadvantages of hard water: it causes fur in kettles and boilers, wastes soap, and is unsuitable for dyeing and tanning processes.
What is the first step in municipal water treatment?
The first step is coagulation, where chemicals like potash alum (KAl(SO₄)₂) or sodium aluminate (NaAlO₂) are added to help particles clump together.
What happens during the sedimentation step of water treatment?
During sedimentation, the flocs settle at the bottom of the tank.
What is the purpose of filtration in water treatment?
Filtration allows water to pass through filter beds to remove any remaining dirt.
What is chlorination in water treatment?
Chlorination (disinfection) is the process of adding chlorine to water to kill germs.
What other chemicals might be added during chlorination?
Iodine and fluorine may also be added during chlorination to prevent goiter and tooth decay.
What is the bond angle in a water molecule?
The bond angle in a water molecule is approximately 105°.
At what temperature does water have its maximum density?
Water has its maximum density of 1 g/cm³ at 4°C.
How do metals like Mg and Zn react with water?
Metals like Mg and Zn react with steam (not cold water) to form metal oxides and hydrogen gas.
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