WATER__________________________________________________________________

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Water

The water molecule is formed by the chemical combination of 2 hydrogen atoms and 1 oxygen atom.

• Water is essential for the existence of life.• All bio-chemical reactions take place in a

water medium.• Nearly 65-70% of the total body weight of

living beings consists of water.

POLARITY AND HYDROGEN BONDING An important feature of water is

its polar nature. The water molecule forms an angle, with

hydrogen atoms at the tips and oxygen at the vertex.

Since oxygen has a higher electro negativity than hydrogen, the side of the molecule with the oxygen atom has a partial negative charge.

An object with such a charge difference is called a dipole meaning two poles.

The oxygen end is partially negative and the hydrogen end is partially positive, because of this the direction of the dipole moment points towards the oxygen.

The charge differences cause water molecules to be attracted to each other (the relatively positive areas being attracted to the relatively negative areas) and to other polar molecules.

This attraction contributes to hydrogen bonding, and explains many of the properties of water, such as solvent action.

WATER-Universal solvent

• Water is called the universal solvent because of it's ability to dissolve or dissociate most compounds. It can do this because of it's polarity. Oxygen has a higher electro negativity (meaning a stronger affinity for electrons) than Hydrogen so the oxygen side of a water molecule is slightly negative and the hydrogen side is slightly positive. In a solution, the positive hydrogen side of water is attracted to the negative parts of the compound it is dissolving while the negative oxygen is attracted to the positive parts. This allows water to dissociate and break apart ionic compounds.

MOLECULAR STRUCTURE OF WATER

A molecule is an aggregation of atomic nuclei and electrons that is sufficiently stable to possess observable properties—

And there are few molecules that are more stable and difficult to decompose than H2O.

In water, each hydrogen nucleus is bound to the central oxygen atom by a pair of electrons that are shared between them; chemists call this shared electron pair a covalent chemical bond.

In H2O, only two of the six outer-shell electrons of oxygen are used for this purpose, leaving four electrons which are organized into two non-bonding pairs.

The four electron pairs surrounding the oxygen tend to arrange themselves as far from each other as possible in order to minimize repulsions between these clouds of negative charge.

This would ordinarily result in a tetrahedral geometry in which the angle between electron pairs (and therefore the H-O-H Bond angle) is 109.5°.

However, because the two non-bonding pairs remain closer to the oxygen atom, these exert a stronger repulsion against the two covalent bonding pairs, effectively pushing the two hydrogen atoms closer together.

The result is a distorted tetrahedral arrangement in which the H—O—H angle is 104.5°.

(Continued in next slide)

BECAUSE MOLECULES ARE SMALLER THAN LIGHT WAVES, THEY CANNOT BE OBSERVED DIRECTLY, AND MUST BE "VISUALIZED" BY ALTERNATIVE MEANS. THIS COMPUTER-GENERATED IMAGE COMES FROM CALCULATIONS THAT MODEL THE ELECTRON DISTRIBUTION IN THE H2O MOLECULE. THE OUTER ENVELOPE SHOWS THE EFFECTIVE "SURFACE" OF THE MOLECULE AS DEFINED BY THE EXTENT OF THE CLOUD OF NEGATIVE ELECTRIC CHARGE CREATED BY THE TEN ELECTRONS.

Electrolytesis a substance which conducts electricity either in liquid or

in solution form

Strong electrolytes : A strong electrolyte is

an electrolyte that completely dissociates in solution. The solution will contain only ions and no molecules of the electrolyte. Strong electrolytes are good conductors of electricity.

Examples: HCl (hydrochloric acid),

H2SO4 (sulfuric acid), NaOH (sodium hydroxide) and KOH (potassium hydroxide)

are all strong electrolyte.

Weak electrolytes A weak electrolyte is

an electrolyte that does not completely dissociate in solution. The solution will contain both ions and molecules of the electrolyte.

Examples: HC2H3O2 (acetic acid),

H2CO3 (carbonic acid),

NH3 (ammonia) are all weak electrolytes.

Classification of electrolytes.

Na+

Cl-

1.Strong Electrolyte -100% dissociation,all ions in solution

High Conductivity

Classification of electrolytes..

CH3COOHCH3COO-

H+

slight conductivity2.Weak Electrolyte -partial dissociation,molecules and ions in solution

Non electrolytes A non-electrolyte does not provide ions in a solution

and therefore current does not flow through such solution.

Examples :-alcohol, carbon tetrachloride, carbon disulphide.

sugar

Non-electrolyte -No dissociation,all molecules in solution

no conductivity

Electrolysis of water is

the decomposition of water (H2O)

into oxygen (O2) and hydrogen gas (H2)

due to an electric current being passed

through the water.

Faradays laws of electrolysis

Faraday's put forward his two laws of electrolysis in 1833.

Faraday's First Law of Electrolysis: Statement:

The mass of an elements which is deposited on an electrode during electrolysis is directly proportional to the quantity of electricity which passes through the electrolyte.

Explanation:

If W is the amount of substance which liberates or deposited at the electrode on passing the electricity through the electrolyte and the quantity of electricity is Q, then

W α Qor W = ZQZ is the electrochemical constant for a given substance.

(Continued in next slide)

Cont’d :-

As, We can write the statement of the first law of electrolysis mathematically as under:or W= ZatIf 1 ampere electric current passes through the electrolyte for 1 second then W=Z It means that on passing the current of 1 ampere for 1 second the weight of the substance deposited is equal to the electrochemical constant. For doing the calculations of electrochemical problems, we must know the units too.

Unit of charge (Q) = Coulomb (C)unit of mass (m) = Kilogram (kg)unit of current (A) = ampere (A)unit of electrochemical equivalent (Z) = kg/C

Note:Faraday's first law of electrolysis is written as:W = ZAtHere;W= is actually mass and not weight, as mass is commonly called weight.

 

FARADAYS LAWS OF ELECTROLYSIS

Faraday's Second Law of Electrolysis:.

Statement: When the same quantity of electricity is passed

through different electrolytes, the masses of the elements liberated or deposited are in proportion to the chemical equivalents of these elements. Faraday's laws are very useful for the determination of electrochemical equivalents of different substances.

Chemical Equivalent: The chemical equivalent of an element is numerically

equal to its relative atomic mass in grams divided by its the valency of the ion.Faraday's second law of electrolysis can also be stated as under:"The mass of different substances liberated or deposited by the same quantity of electricity is proportional to the atomic masses divided by the valencies of their ions."

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EXPLANATION:TAKE THREE SOLUTIONS OF ELECTROLYTES: AGNO3, CUSO4 AND AL(NO3)3 IN A SERIES, PASS SOME QUANTITY OF ELECTRICITY THROUGH THEM FOR THE SAME TIME. NOW AG CU AND AL METALS COLLECT AT THE CATHODE. THEIR MASSES ARE DIRECTLY PROPORTIONAL TO THEIR EQUIVALENT MASSES.

ACCORDING TO FARADAY, IF 96,500 COULOMBS (OR 1 FARADAY) IS PASSED THROUGH THESE ELECTROLYTES,

WE GET  WHICH ARE THE EQUIVALENT MASSES OF

AG, CU AND AL RESPECTIVELY.

Applications of Electrolysis Industrial uses Production

of aluminum, lithium, sodium, potassium, magnesium, calcium

Coulometric techniques can be used to determine the amount of matter transformed during electrolysis by measuring the amount of electricity required to perform the electrolysis

Production of chlorine and sodium hydroxide

Production of sodium chlorate and potassium chlorate

Production of per fluorinated organic compounds such as trifluoroacetic acid

Production of electrolytic copper as a cathode, from refined copper of lower purity as an anode.

Hall-Heroult process for producing galuminium

Electrolysis has many other uses:Electrometallurgy is the process of reduction of metals

from metallic compounds to obtain the pure form of metal using electrolysis. For example, sodium hydroxide

in its molten form is separated by electrolysis into sodium and oxygen, both of which have important

chemical uses. (Water is produced at the same time.)Anodization is an electrolytic process that makes the surface of metals resistant to corrosion. For example, ships are saved from being corroded by oxygen in the

water by this process. The process is also used to decorate surfaces.

A battery works by the reverse process to electrolysis.Production of oxygen for spacecraft and nuclear

submarines.Electroplating is used in layering metals to fortify them.

Electroplating is used in many industries for functional or decorative purposes, as in vehicle bodies and nickel

coins.Production of hydrogen for fuel, using a cheap source of

electrical energy.Electrolytic Etching of metal surfaces like tools or knives

with a permanent mark or logo.Electrolysis is also used in the cleaning and preservation of old artifacts. Because the process separates the non-metallic particles from the metallic ones, it is very useful

for cleaning old coins and even larger objects.

The purest copper is obtained by an electrolytic process, undertaken using a slab of impure copper as the anode and a thin sheet of pure copper as the cathode. The electrolyte is an acidic solution of copper sulphate. By passing electricity through the cell, copper is dissolved from the anode and deposited on the cathode. However impurities either remain in solution or collect as an insoluble sludge. This process only became possible following the invention of the dynamo; it was first used in South Wales in 18

Electrolytic refining

Electroplating• Electrotyping (also Galvanoplasty) is a chemical method for

forming metal parts that exactly reproduce a model. • The method was invented by Moritz von Jacobi in Russia in

1838, and was immediately adopted for applications in printing and several other fields.

• As described in an 1890 treatise, electrotyping produces "an exact facsimile of any object having an irregular surface, whether it be an engraved steel- or copper-plate, a wood-cut, or a form of set-up type, to be used for printing; or a medal, medallion, statue, bust, or even a natural object, for art purposes.

• "[In art, several important "bronze" sculptures created in the 19th century are actually electrotyped copper, and not bronze at all; sculptures were executed using electrotyping at least into the 1930s.

• In printing, electrotyping had become a standard method for producing plates for letterpress printing by the late 1800s.

ELECTROPLATING

The process of depositing a thin layer of one metal over the other metal by electrolysis is called electroplating.

ADVANTAGES of Electroplating

articles made up of cheaper metals can be plated with gold & silver.By doing this the metals appear shining

Prevents rusting of iron

True Solution, Suspension and Colloidal SolutionBased on distinct properties, solutions can be classified into True Solution, Suspension and Colloid. This classification is necessary to understand concepts of colloidal solutions and distinguish it from rest of the types.

SolutionsA solution is a homogeneous mixture of

two or more components. The dissolving agent is the solvent. The substance which is dissolved is the solute. The components of a solution are atoms, ions, or molecules, which makes them 10-9 m or smaller in diameter.

Example: Sugar and Water. SuspensionsThe particles in suspensions are larger

than those found in solutions. Components of a suspension can be evenly distributed by a mechanical means, like by shaking the contents, but the components will settle out.

Example: Oil and Water.

Colloids• Colloids were named first in the early 19th

century by the Father of Physical Chemistry, Thomas Graham (1805-1869). In 1920's and 1930's, the importance of colloids to industrial

processes and biochemistry changed everything making it a hot field.

• A colloidal system consists of an internal phase

(dispersion phase), which is the material of colloidal dimensions, and an external phase (dispersion medium) .Similar to the terms solute and solvent used for simple solutions. • As the particles of a colloid system become

smaller and smaller, we go over imperceptibly from a two-phase colloid to a single-phase solution, and there is no definite boundary i.e.

true solution.

Classification of Colloids:-

One way of classifying colloids is to group them according to the phase (solid, liquid, or gas) of the dispersed substance and of the medium of dispersion.

Dispersion Medium

Dispersed phase

Type of colloid

Example

Gas Liquid Aerosol Fog, clouds

Gas Solid Aerosol Smoke

Liquid Gas Foam Whipped cream, soda water

Liquid Liquid Emulsion Milk, hair cream

Liquid Solid Sol Paints, cell fluids

Solid Gas Foam Pumice, plastic foams

Solid Liquid Gel Jelly, cheese

Solid Solid Solid Sol Ruby glass

Properties of Colloidso One property of colloid systems that distinguishes them from true solutions is that colloidal particles scatter light. If a beam of light, such as that from a flashlight, passes through a colloid, the light is reflected (scattered) by the colloidal particles and the path of the light can therefore be observed. When a beam of light passes through a true solution (e.g., salt in water) there is so little scattering of the light that the path of the light cannot be seen and the small amount of scattered light cannot be detected except by very sensitive instruments. The scattering of light by colloids, known as the Tyndall effect, was first explained by the British physicist John Tyndall.

o When an ultra microscope (see microscope) is used to examine a colloid, the colloidal particles appear as tiny points of light in constant motion; this motion, called Brownian movement, helps keep the particles in suspension. 

o Absorption is another characteristic of colloids, since the finely divided colloidal particles have a large surface area exposed. The presence of colloidal particles has little effect on the colligative properties (boiling point, freezing point, etc.) of a solution.

Properties Suspension Colloid Solution

1. Particle size >100nm 1-100nm <1nm

2. Separation1)ordinary

filtration2) ultra filtration

possiblepossible

not possiblepossible

not possiblenot possible

3. Settling Settles under gravity

Settles onCentrifugation

Does notsettle

4. Appearance opaque Generally clear clear

5. Diffusion Not possible Diffuses slowly Diffuses rapidly

6. Brownian motion shows shows Not observable

7. Tyndall effect shows shows Not observable

Characteristics of Suspension, Colloid and Solution

Uses of colloids:

• Purification of water by alum (coagulation)

• In rubber platting

• In tanning

• Artificial rains

• Formation of deltas (coagulation)

• Blood clot formation

• Colloidal medicine: Argyrols and protargyrol are colloidal solution of silver and are used as eye lotions .Colloidal sulphur is used as disinfectant and colloidal gold, calcium and iron are used as tonics. A wide variety of medicines are emulsions.

• Coating of Photographic plates

• Sewage disposal

• Metallurgy

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