Understanding Water: Properties, Composition, and Corrosion in Water Systems, Lecture notes of Chemistry

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Marathon runner narrowly avoids death after

drinking too much water

• A seasoned marathon runner had no recollection of finishing her race or the fact that she suffered

a seizure once she was back home.

• Johanna Pakenham drank approximately 20 small bottles of water to cope with the heat during

this year's London Marathon.

• Before Pakenham was diagnosed with hyponatremia, a condition which is also dubbed "water

intoxication", her partner needed to perform CPR while waiting for an ambulance.

• Hyponatremia, or water intoxication, happens when you drink too much water and the sodium

levels in your body plummet to an unusual low.

• Sodium is an essential electrolyte in your body, which helps nerves and muscles function

optimally, along with keeping blood pressure stable.

• Consuming too much water causes cells in the body to swell. It also causes the brain to swell –

and the pressure of the brain against the skull could result in seizures. It could also result in heart

failure, respiratory distress and renal distress.

What is H 2 O Physical Properties of H 2 O or as it’s commonly called “water”

• Water is a transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's streams, lakes, and oceans, and the fluids of most living organisms. It is vital for all known forms of life, even though it provides no calories or organic nutrients. Its chemical formula is H2O, meaning that each of its molecules contains one oxygen and two hydrogen atoms, connected by covalent bonds. Water is the name of the liquid state of H2O at standard ambient temperature and pressure. It forms precipitation in the form of rain and aerosols in the form of fog. Clouds are formed from suspended droplets of water and ice, its solid state. When finely divided, crystalline ice may precipitate in the form of snow. The gaseous state of water is steam or water vapor. Water moves continually through the water cycle of evaporation, transpiration (evapotranspiration), condensation, precipitation, and runoff, usually reaching the sea.
• Water is a liquid between 0 and 100oC
• The maximum density of water in its liquid form occurs at 4oC (39.3oF).
• Boiling point at 100oC (212oF)
• Freezing point 0oC(32oF)
• Absorbs light in the blue spectrum hence the blue hue of water.
• A polar molecule, the oxygen atom carries a slight negative charge whereas the hydrogen atoms are positive.
• Water is a polar solvent

What's in a name? From the Greek words hydro and genes, which together mean "water forming.“ Composed of a single proton and a single electron, hydrogen is the simplest and most abundant element in the universe. It is estimated that 90% of the visible universe is composed of hydrogen. Hydrogen combines with other elements to form numerous compounds. Some of the common ones are: water (H 2 O), ammonia (NH 3 ), methane (CH 4 ), table sugar (C 12 H 22 O 11 ), hydrogen peroxide (H 2 O 2 ) and hydrochloric acid (HCl). What's in a name? From the Greek words oxys and genes, which together mean "acid forming.“ Oxygen is the third most abundant element in the universe and makes up nearly 21% of the earth's atmosphere. Oxygen accounts for nearly half of the mass of the earth's crust, two thirds of the mass of the human body and nine tenths of the mass of water. Oxygen is a highly reactive element and is capable of combining with most other elements. It is required by most living organisms and for most forms of combustion. Oxygen can also be combined with acetylene (C 2 H 2 ) to produce an extremely hot flame used for welding. Liquid oxygen, when combined with liquid hydrogen, makes an excellent rocket fuel. Ozone (O 3 ) forms a thin, protective layer around the earth that shields the surface from the sun's ultraviolet radiation. Oxygen is also a component of hundreds of thousands of organic compounds.

NaCl – Salt in solution with water

What's in a name? From the English word soda and from the Medieval Latin word sodanum, which means "headache remedy." Sodium's chemical symbol comes from the Latin word for sodium carbonate, natrium. Say what? Sodium is pronounced as SO-dee-em. Although sodium is the sixth most abundant element on earth and comprises about 2.6% of the earth's crust, it is a very reactive element and is never found free in nature. Pure sodium was first isolated by Sir Humphry Davy in 1807 through the electrolysis of caustic soda (NaOH). Since sodium can ignite on contact with water, it must be stored in a moisture free environment. Sodium also forms many useful compounds. Some of the most common are: table salt (NaCl), soda ash (Na 2 CO 3 ), baking soda (NaHCO 3 ), caustic soda (NaOH), What's in a name? Chlorine is derived from "khloros," from Greek word for greenish-yellow, and in 1810, the name was updated to "chloric gas," or "chlorine." Probably the most known form of a chlorine compound is sodium chloride, otherwise known as table salt. It is used to sterilize drinking water and to disinfect swimming pools, and it is used in the manufacturing of a number of commonly used products, such as paper, textiles, medicines, paints and plastic, particularly PVC. But chlorine also has a dark side: Its natural form is a gas, it is harmful to human health. Chlorine is a respiratory irritant, and inhaling it may cause pulmonary edema — an excessive buildup of fluid in the lungs that can lead to breathing difficulties.

The Origin of Water Hardness

Hard Water

• When water is referred to as 'hard' this simply means, that it contains

more minerals than ordinary water. These are especially the minerals

calcium and magnesium. The degree of hardness of the water

increases, when more calcium and magnesium dissolves.

• Magnesium and calcium are positively charged ions. Because of their

presence, other positively charged ions will dissolve less easily in hard

water than in water that does not contain calcium and magnesium.

• Hard water problems are most likely to occur when water is heated.

What is a water softener?

• A water softener is a unit that is used to soften water, by removing

the minerals that cause the water to be hard.

• Softened water still contains all the natural minerals that we need. It

is only deprived off its calcium and magnesium contents, and some

sodium is added during the softening process. That is why in most

cases, softened water is perfectly safe to drink. It is advisable that

softened water contains only up to 300mg/L of sodium.

Why is water softening applied?

• Hard water causes a higher risk of lime scale deposits in household

water systems. Due to this lime scale build-up, pipes are blocked and

the efficiency of hot boilers and tanks is reduced. This increases the

cost of domestic water heating by about fifteen to twenty percent.

Corrosion reactions

Cl 2 + H 2 O HOCl + HCl

Chlorine and Water Hypochlorous Acid and Hydrochloric Acid

CaSO 4 + H 2 O H 2 SO4 + Ca(0H) 2

Calcium sulfate and Water Sulfuric Acid and Calcium Hydroxide

Corrosion in hot water systems

• Galvanic corrosion

• Caustic corrosion

• Acidic corrosion

• Hydrogen embrittlement

• Oxygen attack

• Carbon dioxide attack

Caustic Corrosion

• Concentration of caustic (NaOH) can occur as a result of steam

blanketing (which allow salts to concentrate on boiler metal surface)

or by localized boiling beneath porous deposits on tube surface.

Caustic corrosion occurs when caustic is concentrated and dissolves

the protective magnetite (Fe3O4) layer, causing a loss of base metal

and eventual failure.

Acidic corrosion

• Low make up feed water pH can cause serious acid attack on metal

surfaces in the pre-boiler and boiler system. Feed water can also

become acidic from contamination of the system (process

contamination of condensate or cooling water contamination from

condensers).

• Acidic corrosion can also be caused by chemical cleaning operations

(overheating of the cleaning solution, excessive exposure of metal to

cleaning agent, high cleaning agent concentration).

• In the boiler and feed water system, acidic attack can take the form of

general thinning, or it can be localized at areas of high stress.