Tag Archives: water

SOLUTIONS PREPARATION 1

Today we’ll start to talk about how to prepare a solution. We need to remember that solutions are formed mixing a solute, which is usually a solid, for example sodium chloride, and a Solvent which is usually water.

To measure water we use special materials as beakers and graduated cylinders, but  they just give us an approximate amount of liquid, so even when they have scales about the amount that we are measuring with them, they are not exact.

Volumetric Flasks, give us an exact amount of liquid, and when we prepare solutions they represent the final amount of the solution, as for example 100 mL or 25 mL.

When we finish preparing the solutions, we storage them. We label these bottles with the Concentration, name, date and MSDS code for the solution. Most of the storage bottles are made of glass but some solutions require plastic materials, as for example Sodium Hydroxide or Hydrofluoric acid solutions.

 

DISSOLUTION

It is the process by which a solute (solid, liquid or gaseous) in contact with a solvent is dispersed forming a mixture in which the components are not distinguishable. The best example of a solution is a salt dissolved in water, the most common salt is the one we use every day at the table by the time we eat, this salt has a crystal form, is composed of ions sodium positively charged, and ions chloride with negative charge.

When a salt crystal is in contact with big amount of water, ions Chloride, negative charged, will be attracted by the positive side of water which are the hydrogen atoms, they take the ions from the crystal lattice, and the original solid pass to same state of the solvent.
The final mix is homogeneous and have the same properties in the whole mix.

In Chemistry is important to know the amount of solute in a solution, this value is known as Concentration of the solution. The concentration of a solution is calculated using

Concentration\text{ of Solution = }\tfrac{Amount\text{ }of\text{ Solute}}{Amount\text{ of Solute + Amount of Solvent}}

Example:
Molarity\text{ = }\tfrac{Moles\text{ }of\text{ Solute}}{Volume\text{ of Solution}}

Next chapter will show different ways to express concentration of solutions.

WATER POLARITY

Water is one of the most important molecules in human life, not only because makes up more than two thirds of human body weight, but also because all the cell and organ functions depend on water for their functioning. Something similar occurs in animals and plants. This means that without water most kind of life on earth would disappear in a few days.

Water is composed of one Oxygen atom and two Hydrogen atoms. Oxygen has six electrons in its valence shell, and needs two electrons to acquire great stability, those two electrons are taken from two Hydrogen atoms.

The molecule of H2O is a three dimensional structure, Oxygen is the centre of the molecule, around him there are two pairs of electrons, and two Hydrogen atoms with angles around 107º among them.

Polarity

Oxygen and Hydrogen have electronegativity values of  3.5 and 2.1 respectively, when they are bonded the shared electrons are attracted to the Oxygen side, leaving the Hydrogen atoms with a slightly positive charge, and producing a final polar molecule.

When a water molecule is surrounded by another water molecule, they will interact each other through those slight charges. This interaction is called “Hydrogen Bonding”, which is a weak electrostatic attraction between slight positive and negative charges of different molecules.