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Sunday, September 23, 2012

Theories of Acid and Base


The Arrhenius Theory of acids and bases
The theory

  • Acids are substances which produce hydrogen ions in solution.
  • Bases are substances which produce hydroxide ions in solution.
Neutralisation happens because hydrogen ions and hydroxide ions react to produce water.


Limitations of the theory
Hydrochloric acid is neutralised by both sodium hydroxide solution and ammonia solution. In both cases, you get a colourless solution which you can crystallise to get a white salt - either sodium chloride or ammonium chloride.

These are clearly very similar reactions. The full equations are:



In the sodium hydroxide case, hydrogen ions from the acid are reacting with hydroxide ions from the sodium hydroxide - in line with the Arrhenius theory.

However, in the ammonia case, there don't appear to be any hydroxide ions!
You can get around this by saying that the ammonia reacts with the water it is dissolved in to produce ammonium ions and hydroxide ions:



This is a reversible reaction, and in a typical dilute ammonia solution, about 99% of the ammonia remains as ammonia molecules. Nevertheless, there are hydroxide ions there, and we can squeeze this into the Arrhenius theory.
However, this same reaction also happens between ammonia gas and hydrogen chloride gas.


In this case, there aren't any hydrogen ions or hydroxide ions in solution - because there isn't any solution. The Arrhenius theory wouldn't count this as an acid-base reaction, despite the fact that it is producing the same product as when the two substances were in solution. That's silly


The Bronsted-Lowry Theory of acids and bases
The theory

  • An acid is a proton (hydrogen ion) donor.
  • A base is a proton (hydrogen ion) acceptor.
The relationship between the Bronsted-Lowry theory and the Arrhenius theory
The Bronsted-Lowry theory doesn't go against the Arrhenius theory in any way - it just adds to it.
Hydroxide ions are still bases because they accept hydrogen ions from acids and form water.
An acid produces hydrogen ions in solution because it reacts with the water molecules by giving a proton to them.
When hydrogen chloride gas dissolves in water to produce hydrochloric acid, the hydrogen chloride molecule gives a proton (a hydrogen ion) to a water molecule. A co-ordinate (dative covalent) bond is formed between one of the lone pairs on the oxygen and the hydrogen from the HCl. Hydroxonium ions, H3O+, are produced.



Note:  If you aren't sure about co-ordinate bonding you should follow this link. Co-ordinate bonds will be mentioned several times over the course of the rest of this page.Use the BACK button on your browser to return quickly to this page.


When an acid in solution reacts with a base, what is actually functioning as the acid is the hydroxonium ion. For example, a proton is transferred from a hydroxonium ion to a hydroxide ion to make water.

Showing the electrons, but leaving out the inner ones:

It is important to realise that whenever you talk about hydrogen ions in solution, H+(aq), what you are actually talking about are hydroxonium ions.

The hydrogen chloride / ammonia problem
This is no longer a problem using the Bronsted-Lowry theory. Whether you are talking about the reaction in solution or in the gas state, ammonia is a base because it accepts a proton (a hydrogen ion). The hydrogen becomes attached to the lone pair on the nitrogen of the ammonia via a co-ordinate bond.
If it is in solution, the ammonia accepts a proton from a hydroxonium ion:

If the reaction is happening in the gas state, the ammonia accepts a proton directly from the hydrogen chloride:

Either way, the ammonia acts as a base by accepting a hydrogen ion from an acid.

NEPAL OIL NIGAM CHEMIST SYLLABUS




LEVEL 5, Senior Assistant Chemist.


THEORY

1.  Acids and bases: Bronsted and Lewis acid-base concept, hard and soft acids and
bases, relative strengths of acids and bases and effect of substituents and solvents on
them.
2.  Refining and purification of metals: Chromatography, ion exchange, solvent
extraction, oxidative refining, parting process, zone refining, Mond's process.
3. Liquid state: Vapour pressure, vapour pressure and boiling point, surface tension and
its determination using Stalagnometer,  viscosity and determination by Ostwald
viscometer, applications of surface tension and viscosity measurements, flash point.
4. Solid state: Crystalline and amorphous solids, classification of solids on the basis of
dominant type of bond.
5. Chemical Kinetics: Concept of rate of reaction, dependence of reaction rate on
concentration, measurement of reaction rate, order and molecularity of a reaction,
rate equations for zero, first and second order reactions, the temperature dependence
of reaction rates, reaction mechanisms, catalysis 2
6. Chemical change and chemical equations: Type of chemical change, factors
governing chemical change, chemical equations, their significance different ways of
balancing them.
7. Hydrogen: Position of hydrogen in the  periodic table, technical preparation,
Laboratory preparation from acids.
8. Oxygen: Position in the periodic table, laboratory preparation from compound
containing high percentage of oxygen, properties, applications, oxides.
9. Water: Hard and soft water, removal of hardness, composition of water, structure
solvent property of water.
10. Carbon Mono-oxide and Carbon Dioxide: Preparation, properties and applications
11. Sulphur: Structure of sulphur
12. Hydrogen sulphide and sulphur dioxide: Preparation properties and applications
13. Sulphuric Acid: Properties and applications
14. Phosphorus: Know about red and white phosphorus
15. Isolation and purification of organic compounds: Sources of compound,
characteristics of organic compound, Extra action of organic substances form natural
sources, purification, crystallization, sublimation, distillation, steam distillation,
washing drying, criteria of purify.
16. Aliphatic and aromatic Hydrocarbons and petro chemicals.
17. Antiknocking properties of petro chemicals.

PRACTICAL 
The candidates will be asked to perform laboratory works from the following topics.
1. Determination of volume, weight etc using deferent measuring tools
2. Determination of Density of materials
3. Determination of refractive index
4. Determination of specific heat capacity and latent of materials
5. Determination of specific gravity
6. To separate deferent materials from the mixture.
7. Use of distillation to produce distillate
8. To neutralize acid with proper solution.
9. To investigate the composition of water by electrolysis.
10.To determine the pH of different unknown solution & using pH paper and universal
indicator.
11.To carry out conductivity experiments on solids & liquids
12.Determine Flash point, Viscosity of Oil


LEVEL 4, Senior Assistant Chemist.

A) INORGANIC CHEMISTRY
1. Periodic classification of elements and physical properties
Periodicity of elements, s,p,d and f blocks, long form of  periodic table, discussion on
properties like atomic,  ionic and covalent radii, ionization potential, screening or
shielding effect, electronegetivity, electron affinity.
2. Acids and bases
Bronsted and Lewis acid- base concept, hard and soft acids and bases, relative strengths
of acids and bases and effect of substituents and solvents on them, pH and H
+
ion
concentration of strong acids, neutralization.
3. Principles of qualitative and quantitative analysis
Solubility product, common ion effect, their application in group separation, principles
of volumetric and gravimetric analysis.
4. Environmental pollution
An elementary study of environmental  pollution (in air and water) arising due to the
presence of dust, carbon, CO, CO2, NOx, Sox, H2S and heavy metals.
5. Refining and purification
Chromatography (column, paper), ion exchange, solvent extraction, oxidative refining,
parting process, zone refining, fractional distillation.
6. Carbon
Allotropes of carbon, preparation and properties of oxides of carbon (CO, CO2), general
knowledge of  source CO2 emission in atmosphere, photosynthesis and carbon
sequestration.
7. Water
Structure of water, solvent properties of water, hard and soft water, hydrogen bonding.
B) ORGANIC CHEMISTRY
1. Organic reaction mechanism
Energetic of reaction, energy profile diagrams,  exothermic and endothermic reactions,
types of mechanisms,thermodynamic and kinetic requirement of reaction, Methods of
determining mechanism.
2. Substitution and elimination reactions
Structure of  alkyl  halides, nucleophilic aliphatic substitution reactions, nucleophiles and
leaving groups, the SN2  reaction (kinetics, mechanism, stereo chemistry and reactivity),
The SN1 reaction (kinetics,  mechanism, stereo chemistry and reactivity),  structure of
alkenes, the E2  reaction (kinetics, mechanism, orientation and reactivity), the E1
reaction (kinetics, mechanism, orientation and reactivity).
3. Aromaticity
Aliphatic and aromatic compounds, structure of benzene, Kekule structure, stability of
benzene ring, Huckel's 4n+2 rule,  electropilic  aromatic substitution reaction, effect of
substituent group, orientation, mechanism of electrophilic aromatic substitution  reaction.
4. Spectroscopic techniques
An elementary study of organic compounds structural elucidation by  uv, ir, nmr and
mass techniques.
5. Purification of organic compounds
Methods of purification of crude organic compound, determination of purity of organic
compounds, principles and practices behind  identification of functional group in organic
compounds.
6. Hydrocarbons
Classification of hydrocarbons, sources of hydrocarbons, nomenclature. Aliphatic and
aromatic hydrocarbons. Alkanes, alkenes and alkynes; nomenclature, preparation,
properties and uses. General knowledge of petrochemical compounds, fossil fuels, flash
point, auto ignition temperature, octane number, anti-knocking .7. Alcohols
Classification, distinction between 1°, 2° and 3° alcohols, industrial preparation of
ethanol, uses of ethanol in industries and as vehicle fuel.
8. Carbohydrates
Classification of carbohydrates, structure of glucose, chemical conversion to alcohol.
C) PHYSICAL CHEMISTRY
1. Atomic structure
Sub atomic particles, their masses and charges, atomic mass unit, Daltons atomic theory,
Rutherford's experiment, Bohr's model,  Heisenberg uncertainty principle, Paulis
exclusion principle, Hunds rule of maximum multiplicity, elementary idea of quantum
mechanical model of atom, quantum numbers, isotopes and fractional weights, nuclear
fission and fusion.
2. Chemical bonding
Valency, octate rule, chemical bonds and lewis structure, ionic and covalent bonds, ionic
character of covalent bond, coordinate covalent bond, metallic bonds, intermolecular and
Van der Wall's forces,  shapes of  compound such as NH3, CH4, PF5,  BF3,
3. Oxidation and Reduction
Electronic concept of oxidation and reduction reactions, oxidation number,  balancing
redox reaction by oxidation number and ion electron methods.
4. Chemical equilibrium
Equilibrium in physical processes, features of dynamic equilibrium, LeChatelier's
principle: effect of pressure, temperature, concentration and catalyst on chemical
equilibrium, equilibrium constant Kp and Kc
5. Gaseous State
Postulates of kinetic molecular theory and their significance, Boyle's law, temperature
scale and Charle's law, Dalton's law of partial pressure the ideal gas law, Molecular
diffusion and Graham's law, molecular collision and mean free path, intermolecular
forces, critical temperature and  pressure, departures from ideal gas law, Vander waals
constants a and b, liquefaction of gases.
6. Liquid state
Vapour pressure, vapour pressure and boiling point, surface tension and its determination
using Stalagnometer, viscosity and determination by Ostwald viscometer, applications of
surface tension and viscosity measurements.
7. Solid state
Crystalline  and amorphous solids, classification of solids on the basis of dominant type
of bond.
8. Chemical Kinetics
Concept of rate of reaction, dependence of reaction rate on concentration, measurement
of reaction rate, order and molecularity of a reaction, rate equations for zero, first and
second order reactions,  temperature dependence of reaction rates, reaction mechanisms,
catalysis
9. Thermodynamics
First law of thermodynamics, thermodynamic terms, iso thermal but not reversible
expansion of an ideal gas, iso thermal reversal expansion of an ideal gas, enthalpy of
physical and chemical changes, Hess's law of constant heat  summation, spontaneous and
non-spontaneous changes, second law of thermodynamics, spontaneity and entropy
change, entropy as a measure  of randomness, a molecular interpretation of entropy, the
free-energy function and equilibrium, free energy and temperature, free energy and the
equilibrium constant, criteria of spontaneity.
D) GENERAL1. Treatment of analytical data
Nature of analytical measurements, significant figures, precision and accuracy, errors,
basic statistical concepts, average and measures of  dispersion, standard deviation,
confidence limits, elements of standards and measures. Data processing in spread sheets.
2. Laboratory management
General idea of safety precaution in the laboratory, care and maintenance of laboratory
equipments.


Sunday, July 29, 2012

MSc chemistry 2nd year result 2012

The result of msc chemistry 2nd year has been published today at 4 :00 pm.