Chemistry Section 4

Natural water purification

A natural system that rids of minerals, metals, organic substances, bacteria, and suspended particles; made up of the hydrologic cycle, bacterial action, and filtration; in a perfect world, could be used to create purified or pure water, but acidic water


The first part of the hydrologic (and natural water purification) cycle, where the Sun heats the water, so that it turns into vapor, leaving behind dissolved substances (heavy metals, minerals, molecular substances)

Condensation/ precipitation

The second part of the hydrologic cycle (and natural water purification process), where water vapor- that is, if not affected by modern airborne pollution- creates tiny droplets of liquid/ The last part of the hydrologic cycle, where water droplets fall t

Hydrologic cycle

The first part of the natural water purification process, that consists of evaporation, condensation, and precipitation; moves in a constant loop as water goes from the ground to the air and back again

Bacterial action

The next part of the natural water purification process, after condensation, where bacteria under the soil convert suspended/ dissolved substances in the water into carbon dioxide/ water/ compounds; these bacteria help purify the water


The last step of the natural water purification process, after bacterial action, where water seeps deeper into the ground, passing through gravel, sand, and rock, which gets rid of waterborne bacteria and suspended matter

Water treatment (pre- use purification)

When water is cleaned by a municipal water treatment plant after it has already been through the natural water purification process, and before it is used in homes and buildings; human- made water purification process


The first step of water treatment, where water from some source (lake, river, etc.) goes through a metal screen to keep out fish, sticks, containers, and other large objects

Pre- chlorination

The second step of water treatment, where chlorine is added to the water ro rid of disease- causing microorganisms


The third step of water treatment, where crystals of alum (aluminum sulfate)- Al?(SO?)?and slaked lime (calcium hydroxide)- Ca(OH)?are added to the water, where they react and form aluminum hydroxide- Al(OH)?, a sticky, gelatinous material that traps susp

Settling/ sand filtration

The fourth step of water treatment, where the aluminum hydroxide with trapped suspended particles from flocculation is allowed to settle at the bottom of a container, while the water moves on to be filtrated through sand (fifth step) to clear any remainin

Post- chlorination

The sixth step of water treatment, where the chlorine levels of the water are adjusted to make sure there's a low but adequete amount


An optional seventh step of water treatment where water may be sprayed or mixed into the air to remove odors and improve its taste

pH adjustment

An optional eight step of water treatment where the pH levels of the water are adjusted by adding lime (clacium oxide)- (CaO), to make it more neutral, ensuring that its acidity does not dissolve pipe metal and cause it to pick up impurities


An optional ninth step of water treatment where approximately 1 ppm of flouride is added to water, to prevent tooth decay


Adding chlorine to water (in municipal water treatment plants), to kill any diease- making microorganisms; 3 ways chlorine is added are to
-Bubble in chlorine gas- Cl?, which is not very soluble in water but creates a compound
-Sodium hypochlorite- NaOCl-

Chlorination cons

Chlorine, under some conditions, can react with organic compounds in water created by decomposing organisms, to form substances that can be harmful to humans in large concentrations; includes THMs; because of this health risk, the EPA concentration in tre

THM (trihalomethanes)

A group of substances that can be created when chlorine reacts with organic compounds in water; a common type is chloroform- CHCl?, which can cause cancer


A substance known to cause cancer, such as THMs like chloroform

Alternative 1- Add a charcoal filter

Pros: Can remove most organic compounds from water; cons: Expensive to install and use, disposal is a hassle, and must be replaced often

Alternative 2- Instead of chlorination, use ozone (O?) or ultraviolet light

Pros: Can disinfect water like chloine can; cons: Can't protect water from bacteria when it leaves the plant, and ozone can be toxic if handled/ used incorrectly

Alternative 3- Eliminate pre- chlorination

Pros: Chlorine can still be added later in post- chlorination; cons: Less chlorine concentration can lead to a build- up of bacteria, and THMs may still be able to form

Hard water

Water that has an excess of dissolved calcium (Ca?�), magnesium (Mg?�), or iron (III) (Fe?�) ions in it; it is usually formed in groundwater, which can pass over limestone, chalk, and other substances that have the three mentioned ions; when hydrogen carb

Hard water problems

Though hard water is not a health concern, it is a financial concern, because it can react with soap to form a flaky ir scummy precipitate (unlike regular water, which lathers up) that stains clothes, skin, and hair; though boiling hard water can remove t

Soft water

Water that is not hard; water can be softened by ion exchange, boiling it (though this forms a solid scale), adding sodium carbonate- washing soda- (Na?CO?), borax, trisodium phosphate, and hexametaphosphate, like Colgan (which makes the hard water ions i


Substances in cleaning products that, unlike soap, do not form precipitate in hard water; many early ones were not biodegradable by bacteria, so when dumped they formed huge mounds of suds, and also had phosphate ions (PO??�) that sped up algae growth; to

Ion exchange

A process to soften water that involves passing hard water through a certain resin, found in home water softeners; first, the resin is filled with sodium cations (Na?�), then hard water flows in, and its calcium and magnesium are attracted to the resin be

Water softener

A tank consisting of an ion exchange resin, that contains millions of miniscule, insoluble beads that attract cations; when the resin is filled with hard water ions, it must be renewed, so concentrated salt water is added, which replaces the hard water io

Reverse osmosis

A process where concentrated water is forced by pressure through a semipermeable membrane to create purified water

Colligative property

A property that depends on the concentration of salt solution, like osmotic pressure


The purified water created from reverse osmosis, when it seperates from salts and dissolved solids