Wednesday, March 13, 2013

Aqueous hydrogen fluoride

Introduction:
Electrolysis is a process of breaking down (or decomposes) a chemical compound into its elements by using an electric current. The electric current is passed through an electrolytic cell, which consists of electrodes and electrolyte. Oxidation or reduction reactions occur in these electrodes. Electrolyte is a substance which contains free ions that make the substance electrically conductive. Electrolyte can be aqueous solution of molten ionic compound or the aqueous solution of ionic compound, alkali, or an acid. Hence electrolysis can be of two types
i) electrolysis of molten ionic compound
ii) Electrolysis of aqueous solutions.
Consider the example of sodium chloride (NaCl). Molten sodium chloride is obtained when we heat it till it melts. Whereas if, sodium chloride is dissolved in water, gives the aqueous solutions of sodium chloride. Solution of water of a substance is called the aqueous solution. Since the aqueous solution contains more than one type of ions, electrolysis of aqueous solutions is entirely different from that of molten electrolyte.

Electrolysis of aqueous solutions:

i)   Electrolysis of aqueous sodium chloride :
In the electrolysis of aqueous solutions, not only sodium chloride will dissociate into Na+ and Cl-, but some of the water molecules will also decompose to give hydrogen (H+) and hydroxide ions (OH-). The reaction of electrolysis of aqueous solutions (of NaCl) can be written as follows,
              NaCl ---> Na+ + Cl-
               H2O ---> H+ + OH-
In an aqueous solution, there can be more than one positive and one negative ion. There is a selective discharge, which means when there is a movement of ions to cathode or anode, only one negative ion and one positive ion will be selected to be discharged.

Electrolysis of aqueous solutions:

ii)  Electrolysis of Aqueous Sulphuric Acid
It is one of the examples of electrolysis of aqueous solutions.
The aqueous sulphuric has three types of ions. They are hydrogen ions (H+), sulphate ions (SO42-), and also hydroxide ions (OH-) from the water. The equation can be written as follows,
H2SO4 + H2O --> 2H+ + SO42- + H+ + OH-
Diagram showing electrolysis of water:
Electrolysis of water
The apparatus used for the Electrolysis of Aqueous Sulphuric Acid
There is more than one type of ion moving to the electrode, there is preferential discharge (also called as selective discharge) takes place.
The chemical reactions occur at anode and cathode is given in the table below.

At cathode

At anode

Here, each hydrogen ion (H+) gains electron and becomes hydrogen atom.

Two of the hydrogen atom will combine and produce hydrogen gas molecule.

Equation:
2H+ + 2e ---> H2

 

Here there is a choice of sulphate ions (SO42-) or hydroxide ions (OH-)

Oxygen is gives off at anode, because of hydroxide ion is easier to discharge.

Equation:
OH- + 4e ---> O2 + H2O

 


Note:
When the electrolysis of aqueous solutions of dilute acids or alkalis is done, the volume of hydrogen given off at the cathode is approximately twice that of the oxygen gas at the anode.

Wednesday, March 6, 2013

Group 14 elements: the carbon family

Introduction:
The carbon family elements in the periodic table that belong to the Group 14 or the IV A family are carbon (C), silicon (Si), germanium (Ge), tin (Sn), lead (Pb) and Ununquadium (Uuq). The carbon family is unique in having one metal, three metals and two metalloids.

Properties of individual elements of the carbon family may be represented by the table below


Name of the ElementRepresented by symbolAtomic numberAtomic weightTypeElectronic configuration of the elements
CarbonC612.011Non-metal[He]2s22p2
SiliconSi1428.0855Metalloid[Ne]3s23p2
GermaniumGe3272.61Metalloid[Ar]3d104s24p2
TinSn50118.710Metal[Kr]4d105s25p2
LeadPb82207.2Metal[Xe]4f145d106s26p2
UnunquadiumUuq114289Metal[Rn]5f146d107s27p2
The electronic configuration in the valence shells of the carbon family elements is ns2, np2.  Sharing of electrons is seen in most of the elements of the carbon family. As the size of the atom is increased, the tendency of the elements to lose electrons decreases. Similarly, the tendency of losing electrons decreases with the increase in the atomic number among the elements of the carbon family. The oxidation states of the elements in the carbon family are usually +4 and +2 for heavier elements because of the inert pair effect.

Individual elements in the carbon family:

Carbon: The first element known to humans and is the fourth most abundantly found element. Carbon exists both in elemental form and as allotropes, the most common being diamond and graphite.
Silicon: Crystalline metalloid that forms the foundation for the age of semiconductors. The common compound SiO2 is abundantly found in earth’s crust.
Germanium: Used in manufacturing of semi-conductor devices. Rarely present in earth’s crust.
Tin: When pure, the metal is silvery white and is very soft. Forms low-melting alloys called solders that connect electric circuits.
Lead: Readily combines with the oxygen in the air forming Pb2O, which results in the dulling of the surface on exposure to air.

Conclusion on carbon family:

The elements in the carbon family include a non-metal, two metalloids and three metals, varying greatly in their physical and chemical properties. These elements occur as elemental forms and in the form of compounds in nature. The elements of Group 14 are relatively non-reactive and usually tend to form covalent compounds with exceptions of tin and lead that form ionic compounds.

Common chemical formulas


Introduction: 
In order to study or describe the elements and molecules in simpler forms, chemical formulas are extensively used. For example simplest formula for water is H20, where H represents hydrogen and O is oxygen and subscript 2 indicates the two atoms of hydrogen element joined together to form a molecule.
Applications of chemical formulas
  • It is used to explain the kinds of atoms and their numbers in compound (or an element).
  • The atoms of every element are characterized by different letters.
  • A subscript is used when more than one atom present in a specific element
  • It states the chemical composition of a compound by means of chemical symbols

Common chemical formulas for everyday substances and some common acids

NaCl- Table salt, NH3 (Ammonia) and CH4 (methane) used for cleanser and a gaseous fuel, C6H12O6 - table sugar or glucose, Air contains mixture of N2, O2, CO2, and other traces gas, H2O2 (hydrogen per oxide)- used as a antiseptic and to bleach or lighten hair, Aspirin - C9H8O4, Hydrochloric acid (HCl),Nitric acid (HNO3),Hydrocyanic acid (HCN), Perchloric acid (HClO4), Sulfuric acid (H2SO4),Carbonic acid (H2CO3)

Some important common chemical formulas are given below

Acetic acid - CH3COOH, Acetone - CH3COCH3, Ammonium hydroxide - NH4OH, Aspirin - C9H8O4, Benzene - C6H12, Boric acid - H3BO3,Butane - C4H10, Caffeine - C8H10N4O2, Calcium carbonate - CaCO3, Calcium chloride - CaCl2, Calcium hydroxide - Ca(OH)2, Calcium oxide – CaO, Calcium sulfate - (CaSO4), Glucose - C6H12O6, Hydrochloric acid - HCl, Hydrofluoric acid - HF, Magnesium sulfate - MgSO4, Manganese dioxide - MnO2, Methane - CH4, Naphthalene - C10H8, Oxalic acid - H2C2O4 , Potassium nitrate - KNO3, Potassium sodium tartrate - NaKC4H4O6 , Potassium oxide - K2O, Potassium sulfate - K2SO4, Sodium bicarbonate - NaHCO3, Sodium chloride – NaCl, Sodium hydroxide - NaOH, Sodium sulfate - Na2SO4, Sodium phosphate - Na3PO4, Sodium tetraborate - Na2B4O7, Sucrose - C12H22O11, Sulfuric acid - H2SO4, Water - H20, Zinc chloride- ZnCl

Chemical compounds


Introduction:
We are going to see about the important chemical compounds.  A chemical compound is one of the pure chemical substance composed of molecules and formed combination of more than one different chemically bonded chemical elements.  Elements are more stable when the compounds are combined to form together.  Some important chemical compound names are organic compound, inorganic compound, biomolecules, organometallic compounds and so on.

Organic compound- Important chemical compound

Some important chemical compounds are
Acetaldehyde:  It is an organic chemical compound and also occurs in coffee.  The general formula is CH3CHO.
Benzene:  Benzene is also an organic chemical compound and it is flammable liquid.  General formula is C6H6.
Butene:  Butylene or butene is an chemical compound.  It is colorless gas.  General formula is C4H8.
Ethene:  Ethylene or ethene is one of the chemical compound.  It is flammable gas and colourless.  The general formula of ethene is C2H4.
Formic acid:  Methanoic acid or formic acid is the carboxylic acid.  The general formula of formic acid is HCOOH.

Inorganic compound- Important chemical compound

Some important chemical compounds are
Aluminium chloride:  Aluminium chloride (AlCl3) is the combination of aluminium and chlorine.
Ammonia:  Ammonia (NH3)is the chemical compound.  It is colourless gas and pungent odour.
Calcium chloride:  It is one of the important chemical compound.  CaCl2 is the combination of calcium and chlorine compounds.
Chromic acid:  Collection of compounds. It is a powerful oxidized agent.
Gallium phosphate:  GaPO4 or (gallium orthophosphate) is a colourless crystal.
Hydrogen chloride:  HCl  combination of hydrogen and chlorine atom and soluble in water.
Magnesium oxide:  MgO is a moisture absorbent.  It used as raw material for making cement.
Nitrogen monoxide:  It is a chemical compound with chemical formula NO.
Biomolecules:

Some important chemical compounds are
Acetic acid:  The general formula is CH3COOH.  It is pungent smell and sour taste.
Cellulose:  The general formula is C6H10O5.  It is one of the organic compound.

Air chemical equation

Introduction :
Air is usually made up of a mixture of so many gases. Air comprises slightly over 20% of oxygen (O2) and in relation to 78% nitrogen (N2). Air also contains surplus quantities of Carbon Dioxide (about 0.03%) and even smaller quantities of other inert gases like Helium, Neon, Argon, etc. It has some low level Ozone O3. Air usually exists as a mixture of all these gases it does exist in the compound form. It also contains small and varying quantity of water vapor. Which we are looking as clouds in the sky.The air chemical equation are give in Table 1
air chemical equation

Air chemical equation:Chief constituent of gases

The chief constituent of air is nitrogen gas followed by oxygen
The first two gases nitrogen and oxygen make up 99.0% of the atmosphere by volume.
Nitrogen is moderately inert because of its strong triple bond holding the atoms jointly in the molecule. Whereas, the oxygen gas is synthesized by photosynthesis and removed by combustion and respiration.

Types of Air chemical equation:

The types of air chemical equation as follows
Reaction with Acetaldehyde: Oxygen gas is used in the preparation of acetaldehyde (ethanol) involves the following steps.
2CH3CH2OH + O2 →2CH3CHO + 2H2O
Further oxidation of ethanoic acid with give rise to acetic acid which on further oxidation with carbon dioxide and water takes place on burning.
2CH3CHO + O2 → 2CH3COOH
Reaction with Aluminum: Secondly oxygen reacts with aluminum metal
Aluminum metal undergoes a combination reaction with O2 (g).
4Al + 3O2 →2Al2O3
Reaction with Copper hydroxide: Copper (II) hydroxide degraded into copper (II) oxide and water when heated.
Cu (OH) 2 → CuO + H2O
Reaction with Heptanes: Heptanes, burns in air to give carbon dioxide
C7H16 + 11O2 → 7CO2 + 8H2OH
Reaction with methyl ter butyl ether: The gasoline additive MTBE (methyl tert-butyl ether), C5H12O2 (l), burns in air.
C5H12O2 + 7O2 →5CO2 + 6H2O
Physical properties of Air chemical equation:
  • Oxygen exhibits its Compressibility that is isothermal properties with the chemical compounds.
  • Oxygen shows high conductivity towards air, water, and other fluids.
  • It has high density gradient against air, water and other fluids, various solids and other common liquids.
  • It is relatively rough to handle because of its high tensile strength.
Check my best blog Types of chemical reactions.

Types of chemical reactions

Introduction :
Chemical reaction is defined as the changing one set chemical reactions into other set of chemical reactions. There is no need to give input to the chemical reactions. Chemical reactions involves the transfer of electrons and the formation of chemical bonds. Reactants are the substance which are involved in the chemical reactions. Nuclear reactions are also takes place in the chemical reactions. There are three types of chemical reactions are present.

Different Types of Chemical Reactions:

There are three types of chemical reactions are present. The three types are defined in the following,
Oxidation reaction and reduction reaction:
Oxidation and reduction reaction are defined as one substance gets oxidised and the other substance gets reduced. Simply it is defined as the loss or gain of electrons. Some of the examples involves in this type of chemical reaction are,
1. Iron and oxygen reaction:
In this example, the ion reacts with the oxygen and it produces oxide. In this the oxidised substance is iron. The chemical reaction is as follows,
4Fe + 3O2 `->`  2Fe2O3
Where
            Fe = iron
            O2 = oxygen
            2Fe2O3  = oxide
2. Ethanol and oxygen reaction:
In this example, the ethanol reacts with the oxygen, thus producing an acid called ethanol. In this the oxidised substance is ethanol.
CH3 CH2 OH + [ O ]    `->` CH3COOH
Where,
CH3 CH2 OH = ethanol
[ O ] = other chemicals
CH3COOH = ethanoic acid
Acid – Metal oxide Reaction:
The formation of salt and water by using the reaction of acid and the metal oxide is called as the acid – metal reaction. The example of chemical reaction is, The acid hydrochloric acid reacts with the metal oxide iron oxide,thus producing  iron chloride and solvent water
3HCl + Fe2O3 `->` FeCl3 + 3H2O
HCl = hydrochloric acid
Fe2O3 = iron oxide
FeCl3 = iron chloride
H2O = water

Three types of chemical reaction

Acid – Base Reactions:
The formation of salt and water by using the reaction of acid and base are called as the Acid-Base reactions. The examples for this chemical reaction are ,
The acid hydrochloric acid reacts with the base sodium hydroxide, thus producing a salt called sodium chloride and solvent water
HCl + NaOH NaCl + H2O
Where,
HCl = hydrochloric acid
NaOH = sodium hydroxide
NaCl = sodium chloride
H2O = water

Another example,
The acid sulphuric acid reacts with the base potassium hydroxide, thus producing a potassium sulphate and the solvent water
H2SO4 + 2KOH K2SO4 + 2H2O
Where,
H2SO4 = sulphuric acid
KOH = potassium hydroxide
K2SO4 = potassium sulphate
H2O = water

Wednesday, February 27, 2013

Ionization energy periodic table

Ionization energy is the electrostatic attraction that changes the trend in the groups and periods of a periodic table

Introduction to Ionization energy periodic table

Ionization energy is the minimum amount of energy required to remove an electron from the outermost orbit of an atom to the minimum distance from the atom so that no electrostatic interaction exists between the separated electron and the cation so formed.

ionization energy

explanation for Ionization energy from periodic table

Electrons present in an atom are attracted towards the nucleus due to the positive charge of protons. Therefore, some energy is required to remove an electron from an atom. This energy is referred to as the "Ionization Energy", as when the electron is removed from an atom, the atom is converted to a positively charged ion.
THe energy required to remove the first electron from a neutral atom is called the First Ionization energy, the energy required to remove the second electron from a positive cation is called the Second Ionization Energy, and so on.

Factors on which the ionization energy of an atom depends(periodic table)

  1. Atomic size:- The greater the atomic size, the greater is the distance of the outermost shell from the protons inside the nucleus. Thus, there is lesser pull of the protons on the electrons of the last shell. Thus, the greater the atomic size, the lesser is the ionization energy of that element.
  2. Nuclear charge:- Greater nuclear charge means greater attraction of the elecrons by the protons inside the nucleus. Thus, if the nuclear charge is greater, it becomes difficult to remove electrons from the outermost shell. Thus, the greater the nuclear charge, the greater is the Ionization Energy.

Varation of ionization energy in the Periodic table:-

  1. Across a Period:- 
    Ionization energy of elements increases as one moves from left to right in a row of the Periodic Table.
    Reason:-As we move from left to right in a row of the Periodic Table, the number of rows in the atoms of successive elements remains the same whereas the nuclear charge increases. This causes the electrons to be attracted more strongly towards the nucleus, and hence, the ionization energy increases.
  2. In a Group:-
    As one moves down a group in the Periodic Table, the ionization energy of successive elements decreases.
    Reason:-As we move down a group, the number of shells in the atoms of elements increases and the atomic number also increases. This causes an increase in the atomic size as well as in the nuclear charge. But the increase in atomic size overcomes the increase in nuclear charge, and thus it becomes more easier to remove electrons from atoms of elements as one moves down a group.