Definition
Chemical test for water: anhydrous copper(II) sulphate (white powder) turns blue when water is present, since it absorbs water to form hydrated copper(II) sulphate — a simple, reliable, colour-based test for the presence of water in a sample.
Physical-constant purity tests: pure water has a fixed, precisely known boiling point (C) and melting point (C) at standard pressure. Dissolved impurities raise the boiling point and lower the melting point — so measuring these two temperatures and comparing them to the pure values tells you whether (and roughly how much) a sample is impure.
The pH of distilled water is (neutral), since it contains no dissolved acidic or basic impurities.
Definition
Distillation in the laboratory: water is heated to boiling in a flask; the pure water vapour rises, passes through a condenser (cooled, so the vapour condenses back to liquid), and is collected separately, leaving behind dissolved solid impurities (which don't evaporate) in the original flask.
Tap water conducts electricity while distilled water does not, mainly because tap water contains dissolved mineral ions (like , , ) which can carry electric current, while distilled water has had these ions removed.
Definition
Gases dissolved in natural water from the atmosphere (via diffusion) include oxygen, carbon dioxide, and nitrogen.
Dissolved oxygen is important for aquatic life because fish and other water organisms rely on it for respiration, exactly as land organisms rely on atmospheric oxygen — without adequate dissolved oxygen, aquatic life cannot survive.
Harmful microbes in natural water mainly come from human and animal waste/sewage contamination, which can introduce disease-causing bacteria and other pathogens.
Heavy metals (e.g. lead and mercury) can contaminate natural water from industrial waste and mining runoff; they're harmful to human health because they accumulate in the body over time (bioaccumulation) and can damage the nervous system and other organs even at fairly low exposure levels.
Definition
Water-borne diseases (spread through contaminated water) include cholera, typhoid, and dysentery. Trachoma is an eye infection disease also linked to poor water quality and hygiene, which can lead to blindness if untreated.
Measures to avoid water-borne diseases: boiling or properly treating/filtering drinking water, ensuring safe sewage disposal separate from drinking water sources, and maintaining good personal hygiene.
Definition
Sedimentation lets suspended solid particles heavier than water settle to the bottom under gravity over time, without any physical barrier — the clearer water above is then carefully separated off. Filtration instead passes water through a physical barrier (a filter medium) with pores small enough to trap and remove suspended solid particles as the water flows through.
Unpleasant odours in water can be removed by treatment with activated carbon, which adsorbs (traps on its surface) the compounds responsible for bad smells and tastes.
Dissolved impurities (unlike suspended solids) can't be removed by simple filtration, since they're mixed at the molecular level — one reliable method to remove them is distillation, which physically separates pure water (as vapour, then condensed) from anything dissolved in it that doesn't evaporate at the same temperature.
Definition
To make domestic water supply fit for drinking, water is typically treated in stages: sedimentation and filtration to remove suspended solids, followed by disinfection (e.g. chlorination) to kill harmful microbes — this combined process removes both physical impurities and biological hazards.
Definition
Fertilizers are substances added to soil to supply nutrients that plants need for healthy growth, replacing nutrients the soil loses as crops are harvested repeatedly.
Essential qualities of a good fertilizer: it should be soluble (so plant roots can readily absorb the nutrients), should supply nutrients in the right proportion for the crop, and shouldn't harm the soil or environment with excessive or persistent residues.
Macro-nutrients are elements plants need in relatively large amounts (nitrogen, phosphorus, potassium, and others like calcium and magnesium). Micro-nutrients (trace elements) are needed only in very small amounts — e.g. boron, copper, and zinc — but are still essential, since their absence causes deficiency diseases in plants even though only tiny quantities are required.
Definition
Nitrogenous fertilizers supply nitrogen, essential for making proteins, chlorophyll, and healthy leafy/vegetative growth — this is why nitrogen-containing fertilizers are added to soil, to replace nitrogen depleted by previous crops and support strong plant growth.
Urea is regarded as a good nitrogenous fertilizer because it has a very high nitrogen content by mass (about ), is highly soluble (so plants can absorb it readily), and is relatively cheap and easy to produce and transport.
Phosphatic fertilizers (like super phosphate, chemical formula ) support healthy root development and increase a plant's resistance to disease. Potassium (potash) fertilizers support overall plant strength, water regulation, and disease resistance as well.
Remember
Excess nitrogenous fertilizer is particularly harmful to paddy rice, since rice is grown in standing water and excess nitrogen run-off can cause excessive vegetative growth at the expense of grain yield, and also contributes to water pollution (eutrophication) in the surrounding paddies and waterways.
Definition
Pakistan faces a severe water shortage due to a combination of factors: a rapidly growing population increasing demand, inefficient traditional irrigation methods that waste large amounts of water, insufficient water storage infrastructure (limited dam capacity), climate change affecting glacier melt and rainfall patterns, and pollution reducing the amount of water that's actually safe and usable.
Remember
Negative effects of everyday plastic use include long-term environmental pollution (plastics don't biodegrade and persist for centuries), harm to wildlife (animals ingesting or getting entangled in plastic waste), and blockage of drainage/sewage systems, which can worsen flooding and water contamination.
Negative effects of water pollutants can be reduced by properly treating industrial and sewage waste before it's released, enforcing regulations against dumping pollutants directly into water bodies, and using safer alternatives to harmful chemicals where possible.
Quick Recap
- ●Chemical test for water: anhydrous CuSO turns white blue. Purity: pure water has fixed boiling (C)/melting (C) points; impurities raise b.p., lower m.p.
- ●Distillation separates pure water (evaporates, condenses) from dissolved solids (left behind); tap water conducts (dissolved ions), distilled water doesn't
- ●Natural water: dissolved O/CO/N (vital for aquatic life); microbes from sewage; heavy metals from industry (bioaccumulate, harmful)
- ●Purification: sedimentation (settling) + filtration (physical barrier) remove suspended solids; distillation removes dissolved impurities; disinfection kills microbes
- ●Fertilizers: macro-nutrients (N, P, K — large amounts) vs micro-nutrients (B, Cu, Zn — trace); urea is high-N, soluble, cheap; phosphates roots/disease resistance
- ●Pakistan's water shortage: population growth, inefficient irrigation, limited storage, climate change, pollution
