Analytical Chemistry: The branch of chemistry deals with the study of analytical methods for qualitative and quantitative analysis of chemical substances. It is the science of chemical characterization
Qualitative Analysis: It deals with the identification of elements, present in a substance.
Quantitative Analysis: It deals with the determination of relative amounts of the elements present in a substance. A complete quantitative analysis involves the following steps
1. Obtaining a sample
2. Measurement and calculation of results
3. Separation of the desired constituent
4. Drawing a conclusion
Methods for Separating the Desired Constituent
Following techniques are commonly used for separating the desired constituent.
D. Solvent Extraction
The process of separation of insoluble solid particles from liquids by passing them through a filter medium is called filtration.
● The insoluble solid particles obtained after filtration is called Residue.
● During filtration, the liquid that passes through the filter medium is called Filtrate.
● The medium used for filtration is called filter medium.
Types of Filter Media
The choice of filter media depends upon the nature of the precipitate and some other factors. Two types of filter media are generally used:
Filter paper Filter crucibles
(1) Filter Paper
A paper used for filtration is called filter paper.
Filter papers of different porosities (pore size) are available. The choice of filter paper depends upon the size of particles in precipitates.
Whatman filter papers No. 41 & 42 are in common use.
Method of Filtration by Glass Funnel and Filter Paper
• Filtration by a glass funnel and filter paper is usually slow.
• The liquid containing solid particles is poured on a glass rod which then goes into the filter paper.
● The residue is collected on filter paper and filtrate is collected in the beaker as shown in fig.
Points For a Good Filtration Process
Property of Filter Paper:
(a) The filter paper must be so large that it is ¼ to ½ full of total precipitates at the end of filtration.
Properties of Funnel:
(b) The funnel should be so large that its upper rim is approximately 2 cm above the edge of filter paper
(c) The stem of the funnel should be several cm long, so that, it goes down into the beaker.
(d) To run filtration smoothly, the stem of the funnel is kept full of liquid, till there is liquid present in the conical part of the funnel ·
(e) The tip of the stem of the funnel should touch the side of the beaker so that the filtrate runs down the side of the beaker without splashing
Folding of Filter Paper
The following are important points
The filter paper should be folded twice
(a) First fold the paper in half along the diameter of the paper.
(b) Second fold the paper in half again, such that the edges of the paper do not quite match
(c) Open the paper on a slightly larger section such that three-fold thickness is on the one-half side and one-fold thickness is on the other half side and apex angle, slightly greater than 60⁰.
(d) Wet the filter paper with water, insert into a 60 ° degree funnel and firmly press down,
Methods to increase the Rate of Filtration
(1) Suction Filtration
Ordinary filtration is very slow. To increase the rate of filtration suction is applied. This is called suction filtration or vacuum filtration. For better suction filtration, filter paper must be tightly pressed.
(2) Fluted Filter Paper
● By using fluted filter paper rate of filtration through a conical funnel can be increased.
● To prepare it ordinary filter paper is folded in such a way that a fan-like arrangement is obtained.
● This fan-like arrangement has alternate ups and downs.
● Thus, the surface area is increased, and hence the rate of filtration is increased.
(2) Filter Crucibles
For suction filtration, filter crucibles are commonly used.
Two types of filter crucibles are generally used.
(a) Gooch Crucible
● It is made up of porcelain having a perforated bottom,
● The perforated bottom is covered with filter paper or with paper pulp.
● For quick filtration, the Gooch crucible is fitted into a suction filtration apparatus.
● It is useful for filtration of precipitates, which need to be ignited at high temperatures.
● Some materials, e.g. conc. HCI, KMnO4 solution react with filter paper. Therefore, they cannot be filtered using filter paper. For such materials, Asbestos Mat is used in place of filter paper.
(b) Sintered Glass Crucible
It is a glass crucible. It has a porous sintered glass disc sealed into its bottom.
It is better than Gooch’s crucible due to following reasons
● No extra preparation is needed
● No filter paper is used. Thus, fibers of filter paper do not make the product impure.
● It can be easily handled Reactive materials (e.g. conc. HCl, KMnO solution) can be easily filtered.