Sunday, June 28, 2009


hi to all i will close this site and will be transferring at this new site see you all there

Sunday, August 05, 2007

acids and bases

Acids are compounds that tend to give up a hydrogen ion (H+). They are usually sour. They react with bases to form salt and water.

Bases are compounds that tend to receive a hydrogen ion (H+). They are usually bitter. They react with acids to form salt and water.

Indicators are compounds that slightly change their structure, and also their color, in the presence of acid or base.

Neutralization reaction is the reaction between an acid and a base, forming a salt and water.
There are numerous acids and bases in our household: vinegar, muriatic acid, car battery acid, lye, baking soda, spirit of ammonia

Acids in the atmosphere are usually produced by nitrogen oxides and sulfur oxides that are released into the atmosphere from the burning of fossil fuels. They may be carried to the ground by rain.

Saturday, August 04, 2007

the mole concept

  1. A mole contains the same number of particles (atoms, molecules, ions). It is a specific number of chemical units.
  2. A mole is a quantity of substance that contains Avogadro’s number of units or particles, which is equal to 6.02 x 1023.
  3. Molar Mass (MM) is the mass in gram of one mole of a substance.
  4. For elements, it is numerically equal to the atomic mass, and for compounds, it is numerically equal to the molecular or formula mass.
  5. The amount of substance can be expressed in three ways:
    Number of particles

factors affecting solubility

1. Effect of Temperature
For some substances to dissolve in a given solvent, heat is absorbed. The reaction is endothermic. In this case, an increase in temperature increases solubility. For some substances, heat is released when they dissolve in a given solvent. The reaction is called exothermic. In this case, an increase in temperature decreases solubility.

Generally, an increase in temperature in the solubility of solids in liquids increases solubility. But for solubility of gas in liquids, an increase in temperature decreases solubility because gas evaporates as temperature increases. .

2. Effect of Pressure
Pressure unlike temperature has little effect on solutions unless the solute is a gas. An increase in pressure causes greater interaction between particles of the gas and the liquid, thus, increasing solubility.

3. Nature of solute and solvent
Nature of both the solute and the solvent affect the solubility.

  • Substances with similar intermolecular attractive forces tend to be soluble in one another. This generalization is stated as "like dissolves like."
  • Non polar solutes are soluble in non polar solvents; Polar or ionic solutes are soluble in polar solvents

  • Liquids that are attracted by charged objects are composed of polar molecules; those that are not attracted by a charged body are non polar


Solubility refers to the amount of solute that can dissolve in a given solvent at room temperature.

How do substances dissolve? Solvation - there is an interaction between the solute and the solvent. The solute particles are usually surrounded by the solvent particles. This process is called solvation.

The nature of the solute and the solvent affects whether a substance will dissolve. If the solute contains charged particles, it will also dissolve in a solvent that has a tendency to have charges. On the other hand, a solute that does not have a tendency to be charged can only dissolve in a solvent that has similar characteristics.

Agitation makes the solute dissolves more rapidly because it brings fresh solvent into contact with the surface of the solute. However, agitation affects only the rate at which a solute dissolves. It cannot influence the amount of solute that dissolves. An insoluble substance will remain undissolved no matter how much the system is agitated.

Rules on solubility:
1. A substance is insoluble if less than or equal to 0.1g dissolves in 1 liter of water at room temperature.

2. A substance is slightly soluble if greater than 0.1g but less than 10 g dissolves in 1 liter of water at room temperature.

3. A substance is soluble if 10 g greater than 10 g of the substance dissolves in 1 liter of water at room temperature.

saturated, unsaturated and supersaturated

Solubility is defined as the maximum amount of solute dissolved by a given amount of solvent at a definite temperature.

The solubility of the given substances in a given solute is temperature-dependent.

Solution containing the maximum amount of solute at room temperature is saturated. When more solute is added into the solution the solute will no longer dissolve.

If the solution contains the maximum amount of solute at an elevated temperature the solution is supersaturated. When more solute is added into the solution, crystals will form.

If the solution contains less quantity of solute than what can be dissolved at room temperature it is unsaturated. When more solute is added into solution the solute dissolves.

how dissolving process happens

The solute and solvent interact to form a homogeneous mixture.

Since it is a homogeneous mixture, it means that the particles of solute and solvent are intimately mixed, so that they cannot easily be identified from each other in the mixture (one phase, one consistency, one texture).

The solvent particles surround the solute particles in the dissolving process.
The solvent and solute particles interact with each other. They have similar polarity. From this comes the saying that “like dissolves like”: Molecules with like polarity dissolve in each other.

If the solvent and solute particles are not similar in polarity, there will be no interaction (oil and water), and the solvent particles cannot surround the solute particles. In this case, they would form a heterogeneous mixture.