## Saturday, August 31, 2013

### Cannizzaro Reaction

The cannizzaro reaction is a redox reaction. Two molecules ( aliphatic and aromatic aldehydes ) of an aldehyde are reacted to produce a alcohol and carboxylic acid in the presence of strong base.

a  -   Keto aldehydes give the product of an intramolecular disproportionation in excellent yields.

Mechanism :

Nucleophilic addition of OH- to aldehyde.

The Crossed cannizzaro reaction, uses formaldehyde as reducing agent.

## Friday, August 30, 2013

### Stoichiometry Equations And Balancing Chemical Equation

Stoichiometry is a branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions. It is the study of the relationship between the number of mole of the reactants and product of a chemical reaction. Stoichiometric equation is a short scientific representation of a chemical reaction. The quantities are expressed as grams or moles.

Rules For Writing Stoichiometric Equations:
It takes practice to be able to write balanced equations. Three step process.

1. Write the unbalanced equation.
2. Balance the equation.
3. Indicate the state of matter of the reactant and product.
• Chemical formulas of reactants are listed on the left hand side of the arrow with a positive sign between them.
• Chemical formula of the products are listed on the right hand side of the equations.More than one product , a positive sign is placed between them.
• Reactants and products are separated by  putting an arrow between them to show the directions of the reaction.
• The equation thus obtained above all three steps is called Skeleton equation. For example the chemical reaction between iron and oxygen producing Fe2O3 is represented by the equation as

Fe + O2 → Fe2O3.
The above equation is not a balanced one. In many cases skeleton equation is not a balanced one.
For example ;
SnO2 + H2 → Sn + H2O
The above equation is not a balanced one. So we must balance the equation by balancing coefficients before the various molecules and to ensure the number of atoms on the left side of the arrow corresponds exactly to the number of elements on the right.
In this case, two oxygen atoms on the left hand side of the equation and only one atom on the write hand side of the equation. So we putting a coefficient of 2 in front of water.
SnO2 + H2 → Sn +2 H2O
Now check the equation is not a balanced one.Because 2 hydrogen atoms on the left hand side and 4 hydrogen atoms on the right hand side.Add coefficients of 2 for left hand side of the hydrogen.
SnO2 + 2H2 → Sn +2 H2O
After balancing and adjusting coefficient, we check the equation is a balanced one. Each side of the equation has 1 Sn atom, 4 Hydrogen atom, 2 Oxygen atom.Finally we specifying the states of matter.
The final equation also indicates the physical state of each substance. The abbreviation are used in these states are,
Solid     (s)
Liquid    (l)
Gas        (g)
Aqueous Solution (aq) .
In the above equation oxides are solid, hydrogen forms a diatomic gas, ton is a solid and water vapor indicates that water is in the gas phase.
SnO2 (s) + 2H2 (g) → Sn (s) +2 H2O(g)
• Important conditions such as temperature, pressure, catalyst etc may be noted above or below arrow of the equation.Upward arrow indicate the gaseous product. Downward arrow indicate the precipitated product.

## Wednesday, August 28, 2013

### Mole Concept

Number of particles of the substance is related to the mass of the substance. Mole is a unit of measurement used in chemistry. A chemical mass unit is defined to be 6.023 × 1023. atoms , molecules , ions or some other units.For Example in chemical equation ,

2H2 + O2 → 2H2O
The above equation implies that 2 mole of dihydrogen and one mole of dioxygen react to give 2 mole of water. The mole may also be used to express the number of atoms , ions, or some other substances. But the concentration of solution is commonly expressed by its molarity , defined as the number of moles of the dissolved substance per litre of solution.

The mole may be defined as the amount of the substance that contains as many specified elementary particles as the no.of atoms in 12g of carbon-12 isotope. (i.e ) one mole of an atom consists of Avogadro number of particles.

Example for mole substances :
A mole of oxygen atom contain 6.023 × 1023 oxygen atoms.
A mole of oxygen molecule contains 2 × 6.023 × 1023 oxygen.

Example for ionic substance :
A mole of Sodium carbonate ( Na2CO3 ) quantity containing 6.023 × 1023  , Na2CO3 units. Each formula units of sodium carbonate contains 2 × 6.023 × 1023,  Na +  ions and  1 × 6.023 ×1023  CO32-   ions.

In Chemistry Avogadro number is defined as the number of particles ( atom or molecule ) found in one molecule of a substance. It is a number of atom in a 12 g sample of carbon- 12. It has dimensions of reciprocal mol and its value is equal to 6.0221367  × 1023 .per mole, which is 6.023

## Friday, August 23, 2013

### Uses of alums.

• Alum is used in fire extinguishers to smother chemical and oil fires.
• Alum is a component of foamite.
• Styptic pencils containing aluminium sulfate are used as astringents to prevent bleeding from small sharing cuts.
• Purification of drinking water as a chemical flocculant.
• Pickling agent to help keep pickles crispness.
• Alum is used as the acidic component of some commercial backing powders.
• Alum is an ingredient in some homemade modeling compounds intended for use by children. (Play Clay )
• Alum is used in tanning.
• Alum is used to fix pigments on a surface.
• Alum is an ingredients in some hair removal waxes.
• Alum is used in skin whitener.

### Selenate alum

Alums are also known that contain selenium in place of sulfur in the sulfate anion making selenate    SeO42-   instead . They Known as selenium or selenate alums. The selenium containing alums are strong oxidizing agents, so they used in antiseptics, among other uses.

### Aluminium sulfate ( Papermaker's alum )

Aluminium sulfate is otherwise known as papermaker's alum. However it is not technically an alum. It's properties are quite different from other alums. Most of the industrial flocculation done with alum is aluminium sulfate.

## Wednesday, August 14, 2013

### Chrome alum

Chrome alum is otherwise known as Chromium alum. Chemical formula is              KCr(SO4)2.12H2O. It is a dark violet crystalline double sulfates of chromium and potassium. The dark violet compound is used in tanning and can be added to other alum to grow lavender or purple crystals.

### Ammonium alum

Ammonium alum is otherwise known as Ammonium aluminium sulfate. Chemical formula is
NH4Al(SO4)2.12H2O. It is a white crystalline double sulfates of aluminium. Ammonium alum finds applications in tanning, dyeing textiles, making textiles flame retardant in the manufacture of porcelin cements and vegetable glues, in water purification and in some deodorants.

### Soda alum

Soda alum is otherwise known as sodium aluminium sulfate. Chemical formula is NaAl  (SO4)2.12H2O. It is very soluble in water.And is extremely difficult to purify. It is used in baking powder and as an acidulent in food.

### Potash alum ( Potassium aluminium sulfate )

Potassium aluminium sulfate is otherwise known as potash alum or potassium alum. Chemical formula KAl (SO4)2.12H2O . Naturally occuring mineral potash alum is known as alum - (K). Other potassium aluminium sulfate minerals are alunite and kalinite. It is used as an astringent and antisepsis in various food preparation processes such as a flocculant for water purification among other things.

### Alum

Alums are double sulphate salts. Alum is in reference to potassium alum. It is a compound of hydrated potassium aluminium sulfate with chemical formula KAl(SO4)2.12H2O. Any of the compound with the empriocal formula AB(SO4)2.12H2O.are considered to be alum. A is a monovalent cation such as potassium or ammonium. B is a trivalent metal ion such as aluminium or chromium. Some times alum is seen in its crystalline form, although it is most often sold as a powder.

Types of alum :

• Potash alum
• Soda alum
• Ammonium alum
• Aluminum sulfate
• Selenate alum
• Chrome alum

### Amalgam

An alloy of mercury with one or more other metals. Almost all metals can form amalgams with mercury. ( excepting iron  ). Amalgam may be solid or liquid.Silver-mercury amalgam are important in dentistry. Gold-mercury amalgam is used in the extraction of gold from ore.

Types of amalgam :

• Dental amalgam
• Potassium amalgam
• sodium amalgam
• Ammonium amalgam
• Aluminium amalgam
• Thallium amalgam
• Tin amalgam
• Gold amalgam