Wednesday, March 31, 2010

Meniscus



A meniscus is formed because the surface tension will attract the water solution to the molecues of the container thus lifting it up on the edges.

It is due to what is called cohesion and adhesion. The water molecules are attracted to each other through cohesion, which is the attraction between similar particles (by polarity). Adhesion is attraction between unlike molecules. When water is placed in a glass container, the forces of cohesion overcome the forces of adhesion, and the water climbs up the glass.
Conversely, the attraction between mercury atoms (cohesion) is stronger than its attraction to the glass (adhesion). Therefore, the atoms pull together and away from the glass.

Cylinder, Pipette and Burette





A cylinder is the one of the most curvilinear geometric shapes,
the surface formed by the points of a fixed distance from a given straight line, the axis of a cylinder.



Pipette are devices that allow the users to extract or deliver small amount of liquid.
A pipette uses a bulb to dispense appropriate quantities of effluent.




A burette is a vertical piece of cylindrical piece of laboratory glassware with volumetric graduation on its full length and a presicion tap, or a stopcock, on the bottom . It is used to dispense known amouts of liquid regents in experiments which such precision is necessary.
The difference between the cylinder, pipette and the burette.
They measure volumes of liquids, however,
1)The burette has a tap to control the flow of liquid while the cylinder and the pipette do not have. a
2)The pipette uses a bulb to dispense appropriate quantities of liquid
3) The measuring cylinder is a graduated container with a spout unlike the pipette and burette.