What is Chemical Analysis?

       In Simple words chemical analysis is finding out the substance present and the amount of the substance present in a sample. Finding out the substances present is called qualitative analysis and the amount of the substances presence is called qualitative analysis.

Example : Look at a water bottle available for sale.

                  Does the label give the composition of the ions/elements present as percentages ?

                  Yes. The manufacture of this water brand has done a sample testing for quality and 

                  qualitative analysis. 

       If you consider the above example , each and every bottle carries this label. Do you think he has checked each and every water bottle ? No. It is practically impossible (Although it should been done.) What must have he done ? He must have checked some water bottles (samples) of the production. This is called sampling. He has taken few samples from a batch of bottles or a population of bottles. Let us see what these terms really mean. 

Population and Sample

What is a population ?

      It is an actual or conceptual collection of individual items/ observations /  measurements , which may be finite of infinite.

Example :  1. Students in a university

                   2. Inland waters of Sri Lanka

                   3. Soil in the Anuradhpura District area 

                   4. The effluent of a paint factory 

                   5. Blood of a patient

                   6. Results of a tit-ration

What is a Sample ?

       

        A sample is a small part of the population, taken for analysis.

Example : A water sample of a well be of about 1 L.

       When the size of the sample or number of samples is large, its properties will be very much closer to the population. Therefore, if you want test your well water it is better to take at least about three samples of 1 L each.

Population and a sample

        In the determination of a characteristic of  population, taking measurements of the whole  population is not possible. Therefore, we have take samples from the population for the determination.

Let's explain this more by trying to answer the following question. 

        Can you find the average weight of children of age five in the Colombo district?

You can . What should you do in Oder to find out the average weight ? You have to take the weight of each child and average it. Is it an easy task? How much of time and how many people should be employed for this ? Here, the population is the total number of children of age five in the district of Colombo. It is not an easy task. This is because we can't take measurements form all units/ individuals of due to various reasons. It may be due to lack of time, energy, money  etc.... If so, is there another way to find the average weight of children of age five in the Colombo district ? 

       Yes. There is . We have to take a sample of children having a number we can cope with. then we can take the weight of the children in the sample and take the average. The sample should not be biased. What does this mean? Samples should be randomly selected in order to be true representatives of the population. 

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Posted at 11:28 PM |  by Unknown

Occurrence and isolation

          Alkali metals are reactive and they are not found in nature as free metals.Sodium and potassium are relatively more abundant than the metals in this group. Na is present as a salt (sodium chloride, NaCl) in huge quantities in underground deposits (salt mines), in seawater and other natural waters. Potassium salts are found naturally in seawater, and as carnality, KCl-MgCl₂-6H₂O or ptash (KOH). The concentrations of Na⁺ and K⁺ions in seawater are 10,800 and 590ppm, respectively.

Sodium and lithium are obtained by the electrolysis of their molten chloride. For example.

During electrolysis Na⁺ ions are reduced to Na metal and chloride ions are oxidised to chlorine gas.

Potassium is made by the reaction of sodium vapour with molten/fused KCl at 850⁰C.

Rubidium and cesium are made by the reduction of their chlorides with calcium metal at 800⁰C.

All isotopes of francium are radioactive.

Some properties of alkali metals

           In this session, we will mainly concentrate on the chemistry of Na, K, and Li. The elements of Group 1 are soft metals and they conduct electricity and heat. Table 1 provides you with some of the physical data of Group 1 elements. As one would expect the ionic radius, r(M⁺), increases as you go down the group. The melting point (m,p) decreases from Li to Cs. Alkali metals have low densities and the densities (d) of Li, Na, and K are less than that of water thus these metals float on water. 

Some properties of group 1 elements

	R(M+)/pm	En Configuration	m.p./0C	d/gcm-3	E0	IE1 kjmol-1	IE2 kjmol-1
Li (Litium)	60	2s1	181	0.53	-3.04	520	7590
Na (Sodium)	95	3s1	98	0.97	-2.71	496	4560
K (Potasium)	133	4s1	63	0.86	-2.94	418	3060
Rb (Rubidium)	148	5s1	39	1.53	-2.94	401	2630
Cs (Caesium)	169	6s1	29	1.90	-3.03	376	2430

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Posted at 12:07 AM |  by Unknown

What is a Measurement?

               Measurement is a comparison of something to be measured with some agreed stand. For example, let us suppose that we want to take the pen as a unit of length. Then the lengths of all the objects could be related to the length of the pen. One object may be twice as long as the length of the pen. A second may be two and half times as long and so on. Once the unit is established, measurement becomes simply a matter of counting. So, if we say that a tree is 1000 "pen lengths" high, you will have some idea of how tall it is even though you do not see it. But you must know what the unit of measurement is. Thus, we need standards, and these standards must be know by everyone with whom we wish to communicate. Now, let us see the standards we choose.

Fundamental Units:

                 We have already stated that in making a measurement, we have to express the quantities in terms of known standard quantities of length, mass and time. The basic idea of selecting standard unit is that they should be constants independent of time and location, easily obtainable and reproducible so that all countries in the world can duplicate them and keep them as references.

Standard of length:

                 The standard unit of length is the meter. This is defined as the distance between two points made on a bar of platinum-Iridium alloy kept at 0C at the International Bureau of weights and Measures in Paris and France.

Today, all distances are measured in terms of the metre.

However, it was difficult ta make replicas and maintain them in the laboratory. So, in 1960, a new standard was adopted which was easier to reproduce and measure experimentally. When an electron jumps between the energy levels 2p and 5d of an isotope of Krypton-86, it emits a characteristic radiation. (Orange-red light). In a comparison of the wave length of this radiation with the standard metre it was seen that the standard meter is equal to 1650763.73 wave lengths of the krypton line.

Therefore, the metre is redefined as "the length equal to 1650763.73 wave lengths of a orange -red light emitted by the Krypton-86 atom"

Standard mass:

The standard unit of mass is the kilogram. This is also kept at the international Bureau of weights and measures in paris and denotes the mass of a standard cylinder made of platinum-iridium ally. All masses are compared with this mass which is called the standard kilogram.

Standard time:

Until recent times, the standard unit of the solar second. This was 1/86400 part of the mean solar day.

A better standard was then introduced and a second was redefined as 1/31556925.9 of the tropical year 1900. As the length of the year is not constant, this definition was discarded.

In 1967, the standard was equated again to agree with more precise and easily available data. 

Thus, the standard of time, "the second" was defined as the time taken for a Cesium atom of atomic mass 133 to vibrate exactly 9 192637770 times.

As stated above the Fundamental Units of length mass and time are metre, kilogram and second. the system using these units, for measurements is called the M. K. S. (meter, kilogram, Second) . But in our study in physics we require to define several more units for basic quantities. This is called the SI system of units.

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Posted at 7:37 AM |  by Unknown

Animal Cells I

Cells and their contents

                  The Cell is the smallest unit that retains the properties of life. It is the basic structural and functional unit of life. It is often called the building block of life. Its structure is highly organized for metabolism. It senses and responds to its environment. There are two different types of cells and they form the sharpest and clearest division in the living world, rather than between plants and animals. These are the Eukaryotic cells with true nuclei and prokaryotic cells without organized nuclei. prokaryotes were the first life form on earth. You have already learnt about them in the General Biology. The basic difference in the structural organization of these two cell types are listed below for you to see whether you can remember them.

• Prokaryotic cells are smaller and simpler than Eukaryotic cells. They are less than 5um in diameter and on average 10 times smaller than Eukaryotic cells. 

• Prokaryotic cells have cell walls composed of peptidoglycan (amino acid and sugar). Some eukaryotic cells also have cells walls, but none are made of peptidoglycan.

• Prokaryotic cells do not have cytoskeletons while all eukaryotic cells have them.

• Membrane bound organelles such as mitochondria, chloroplasts, lysosomes, nucleus and membranous tubular canals such as endoplasmic reticulum, Golgi bodies are absent in prokaryotes while they are present in eukaryotes.

• Ribosomes of prokaryotes are of 70S smaller type. Eukaryotes have larger ribosomes of 80S type.

• Prokaryotes have a single loop of DNA (circular DNA ) not associated with any protein to form chromatin. DNA is linear in Eukaryotes and associated with protein to form chromatin.

• In Prokaryotes, the cytoplasm has a region that contains DNA and it is know as the nucleoid region, but there is no nucleus. In eukaryotes, the DNA is surrounded by a nuclear envelop, which is a double membrane with nuclear pores. Also, a nucleolus is present in the nucleus , which is involved in making ribosomes and processing mRNA.

• A flagellum of Prokaryotes is a rigid rotating one with the motor embedded in the cell membrane. A flagellum/cilium in Eukaryotic cells is composed of microtubules and motor proteins surrounded by the cell membrane.

Eukaryotic cells are found in the in the organisms of domain Eukarya, in its entire four kingdoms; protista, fungi, plantae, and Animalia.

All the Eukaryotic cells are surrounded by a plasma membrane/cell membrane. Inside the plasma membrane is the cytoplasm consisting of a semi fluid matrix. A variety of organelles such as, nucleus, endoplasmic reticulum, golgi apparatus, lysosomes, ribosomes, mitochondria, plastids, and vacuoles are embedded in this fluid matrix. Organelles are intracellular structures that carry out specific functions. Many are membrane enclosed and are regulated compartment in which a specific chemical environment can be maintained. 

Now, we will look in to the structure and function of animal cell components briefly. We will be dealing with the plant cell components in the next section, when we look at the differences between the plant cell and the animal cell.

Being Eukaryotic cells all animal cells possess nuclei and other membranous organelles characteristic of complex cells. Unlike plant cells their shapes very very much. Like plant cell most animal cells are between 1 and 100 um and therefore are visible only under the microscope.

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Posted at 10:59 AM |  by Unknown