Qualitative And Quantitative Analysis

In General Chemistry there is a branch called Analytic chemistry, which is responsible for discover the properties of chemicals and turn them into useful data when doing more experiments in the laboratory.

Analytical Chemistry is so named because his way of working is through Analysis, which are procedures in which a sample of matter is studied. As the matter is so diverse, the Analyzes come to take various names according to its nature: Clinical Analysis, Food Analysis, Industrial Analysis, etc.

The analyzes are carried out using several methods that will be convenient for the moment. know with the greatest certainty the identity and composition of the matter.

Analytical Methods fall into two simple categories: Instrumental Methods and Chemical Methods.

The Instrumental methods they lean on devices that will aid in the measurement of certain characteristics of chemicals. There are in this type of Method the optical devices, which measure, for example, the index of refraction; furthermore, the

electrochemical devices, like galvanic cells, to measure redox potentials; and others more specific.

In the Chemical Methods, which are the ones who will receive priority this time, there are two types of chemical analysis according to its objective in the matter: Qualitative Analysis and Quantitative Analysis. The purpose of Qualitative Analysis is to discover what substance is present in the sample. And the objective of Quantitative Analysis is to know the Quantity of a certain substance that exists in the sample.

Chemical Methods are characterized by being based on chemical reactions, and although the usual classification is Qualitative and Quantitative, most of the methods analytical are capable of providing qualitative and quantitative information, according to the parameters that are used.

Qualitative analysis

It serves for identify or recognize chemical elements or groups found in the sample. It is to say "What is" the substance present.

It can be divided, according to the chemical nature of the samples being handled, into Organic and Inorganic.

In the Qualitative Organic Analysis, attention is paid to identification of the elements and functional groups that make up the sample. Since it is organic matter, the structures sometimes become very complex, and the systematization more difficult.

Successful analyzes have been achieved by some instrumental methods used in determining the structure of organic compounds. Thanks to this success, these methods, such as spectroscopy, are applied more frequently and in a larger field. ultraviolet, visible or infrared, nuclear magnetic resonance, chromatography and spectrometry of masses.

In the Inorganic Qualitative Analysis, the priority is recognize ions, i.e. cations and anions. There are two definite trends in this type of analysis; the first consisting of use systematic marches, based on the separation into groups, and the second, which is based on the direct identification, without separations.

Quantitative analysis

By having the fundamental objective of look up exact amounts of substance, Quantitative Analysis is based on the application of the laws of Stoichiometry. We proceed by taking a well-determined quantity of sample, with a known weight or volume, and subjecting it to chemical reactions that take place as completely as possible, and in which the component to be determined is involved, deducting the amount sought of weight of the reaction product, in the case of Gravimetric Analysis; or of volume of reagent consumed, for Volumetric Analysis.

Almost all the analyzes that exist are quantitative. The Qualitative type identification is always going to be first than the Quantitative one. First you know what to measure, and then how much to measure. The results of the Qualitative Analysis help to choose the method to be used to measure the quantities in the subsequent Quantitative.

The importance of the sample

It's essential obtain a representative sample of the material compositionSince if this representation is not fulfilled, the results obtained cannot be applied to the entire set of material from which the sample is taken.

Sampling is a statistical matter, and it can be a bit difficult considering that sometimes a few tenths of a gram can represent tons of the source material. On the other hand, the sampling problem is so broad that there is no General Theory on Sampling. The sampling situations for the three states of matter are outlined below.

For him gas sampling, the consideration is that gases are generally homogeneous and can collect samples in flasks under vacuum or by displacement of the air initially present in them.

In the case of liquid sampling, a liquid consisting of a single phase is homogeneous if it has been vigorously stirred. In a liquid that is at rest, samples can be taken at different depths, and in the case of a liquid stream, samples should be taken at equal time intervals.

When you are working with solid samples made up of a large number of small pieces, such as a cargo of coal or aluminum ore, it is necessary to take a initial sample or raw sample, larger than can be subjected to analysis in the laboratory, and then systematically reduce it in size, until the adequate sample for our procedure is obtained.

To take the gross sample, it is necessary to choose several portions of different parts of the shipment and then put them all together. In the case of a product stored in bags, it is necessary to take a portion of all the different bags, at different depths.