Physical processes in science

TECHNOLOGY

By MICHAEL JOHN UGLO
THIS is the second lecture in the science in action series on Matter. The topic is on the physical processes in Science and Technology.
There are foremost two processes of matter that go on in nature. These are the physical and the chemical processes and changes. Solids, liquids and gases can undergo the physical processes to change from one form to another without a change in their atomic and chemical makeup. For example, water and its chemical symbol is H2O. The symbol H2O means two atoms of H (hydrogen) element are bonded or combined chemically with one atom of O (oxygen) to form a molecule of H2O (water). Water can be in solid form (ice), liquid form and gaseous form (water vapor). In all of these three states they still have the chemical formula H2O.
Physical processes like heating can change one form of matter to another. Heat can change ice (solid) to liquid (water) and liquid to gas. This is called melting. Further application of heat to liquid can make the atoms gain enough energy to change from liquid to gas. This physical process is called evaporation. Now, gases can be cooled to change back to liquid and this is called condensation. From liquid, it can be further cooled to change back to solid and this is called freezing or solidification. In the process of cooling heat is sucked out and therefore the particles lose energy so they have to come closer together to keep themselves warm to form a regular arrangement.
In the other chemical substances like a dry ice (frozen carbon dioxide) heating it will change it directly to a carbon dioxide gas. This physical process is called sublimation. The dry ice is said to sublime to carbon dioxide gas. Likewise, removing heat from it or cooling carbon dioxide will change it into a dry ice. This reversed physical process is called decomposition which is the opposite of sublimation.
Solid particles are packed very closely together. Hence, their arrangement is regular. The liquid particles’ arrangements are irregular. They take the shape of the container they are poured into or occupy. The particles appear far apart in liquids and for that reason the flow. The gas particle arrangement is random. They can quickly escape into space when they are freed.
Physical methods can be used to separate the constituents of a mixture. For instance, to separate a solid and a liquid like water from sand, there are two physical methods that can be used. One is called decantation. That is water is just poured out by tilting the container making sure that the sand does not come out with it. The other method is called filtration. A filter paper is used to pour water out while the sand is withheld by the filter paper. A filter funnel can also be used to do the separation as well.
To separate a mixture of a metal from a non-metal, such as an iron filing and a powdered sodium a bar magnet is used and can be held close to the two mixtures and only iron filling come off and attach to the magnet while the powder is left behind.
There is yet another physical method to separate two or more than two soluble substances. The method is called chromatography. In this method all the dissolved solutes in a solution can be separated. A chromatography paper is dipped into the solution leaving part of it outside and not wet for the solution to be conducted along the paper. The solution travels up the paper and carries with it the solutes. Solutes with the greatest solubility will travel up ahead of the other solutes with lower solubility.

All the solutes will travel up the chromatography paper but directly proportional to their level of solubility with the most soluble furthest than the least soluble seen below in their descending orders. The chromatography paper known as the chromatogram with the solutes on it is taken away for analysis to determine what solutes are contained in the solution.
Solids can be soluble or insoluble that is they can be dissolved in water or not respectively. Soluble solids can dissolve in water. The solids that cannot dissolve in water are called insoluble solids. The soluble solid is called a solute and the liquid part which is the water is called the solvent. A solute added to a solvent gives a solution. How soluble a solute is can be measured by its solubility. Solubility is a measure of how much solute that will dissolve in 100g of water at a particular temperature. Temperature is very important because when you apply more heat, more solutes will dissolve in the solvent because it will give more energy to the water particles to move a part providing space for the solute particles to fit in the inter-molecular spaces of water. Water is made of water molecule (H2O) so the spaces between the water molecules are called inter-molecular spaces.
A fluid such as air or a liquid can spread through space or spread in space through a process called diffusion. Diffusion is movement of particles from an area of more concentration to an area of less concentration. For instance, if you are in a room and someone is at the doorway and applies a perfume to his or her body, you will eventually smell the perfume. The perfume particles have diffused through the air particles from an area of higher concentration (doorway) to an area of lower concentration (where you are).
Also, if you add a colored dye to a bottle of clear water, leave it there for some time and come back after an hour or so to check, you will realise that the water is dyed or evenly colored. That is, the dye had diffused or spread evenly through the water particles (or water molecules). Two factors to be considered are the temperature and pressure. The law of diffusion is covered in Graham’s law which states that “the absolute rate at which a gas diffuses is inversely proportional to the square root of its density.
Rate of diffusion of gas ? 1/sqr Density of gas
The Avogadro’s hypothesis states that, each volume of different gases contains the same number of particles under the same temperature and pressure. Therefore, the mole has to be constant under this same temperature and pressure. Mole is the number of particles (6.02 x 1023) as a reference point taken from 12 grams of Carbon-12 atoms.
Hence, these formulae can be used.
Rate of diffusion of gas ? 1/sqr density of gas and
Rate of diffusion of gas A /Rate of diffusion of gas B =sqr molar mass of gas B/sqr molar mass of gas A.
The particles at the constant temperature are affected by pressure according to the Henry’s law as formulated by an English chemist. P = kc which stands for P = partial pressure of the gas in the atmosphere, k = is a constant and c = is the concentration of the dissolved gas in mol/L.
The solutes and solvents that cannot dissolve any further are at equilibrium. The solution is therefore saturated. Adding more solute to it will fall to the bottom of the solution. When saturated solution is heated further, it will dissolve more solutes. Here, the solution is supersaturated.

Hence, the solution is said to become more concentrated. Concentration thus, is the amount of solute contained in a given volume of solution at a certain temperature. Thus, concentration is directly proportional to temperature. That is, when heat is applied to a saturated solution, the concentration increases because more solutes will be dissolved in the solution.
Solubility of gases in the water is inversely proportional to temperature. That is, when temperature is increased, the solubility of gasses decreases. There is no clear relationship in temperature with liquids to dissolve in liquids. They increase or decrease with temperature and sometimes show no effect at all.
The gas solutes can be added to liquids under pressure. One such is in the soda drinks whereby carbon dioxide is added under pressure producing the carbonated drinks to keep the drinks safe from microbial infections. When the lids of the carbonated drinks are removed, it will result in effervescence producing the fizzing sound.
Liquids that do not dissolve in each other are called immiscible liquids. Such liquids as petroleum and water are immiscible liquids with water being less dense lies on top of the petroleum which is more, denser. In such a case, the liquids can be separated simply by methods such as decantation.
Two liquids that can dissolve in each other are called miscible liquids. These can be separated by distillation. That is depending on their boiling points, one with the lowest boiling point evaporates first when heated in a distillation chamber and with a condenser is condensed and collected as a filtrate.
More than two liquids that dissolve in each other can be separated by fractional distillation. An example is petroleum which is generally referred to as a rock product. It comes from crude oil. It has all the hydrocarbon fuels as diesel oil, gasoline, kerosene, aviation fuel, paraffin, jet fuel and so on in it. So, to separate each fuel from the crude oil it is firstly heated under an intense heat in a distillation chamber.
Crude oil is cracked and heated with intense heat to allow for the respective vaporizing temperatures of the constituents to cool and be distilled from a fractionating column. The ones with the lowest boiling points are vaporised and distilled first followed by the next fuel with the next increased boiling point and so on until the final fuel with highest boiling point is eventually distilled and collected. Those products of the distillation are called distillates.
Solids can dissolve in solids. Examples include metal alloys such as brass, bronze and steel. Apart from covalent compounds like the gasses and water, some ionic compounds can dissolve in water and some cannot. Such compounds that can dissolve in water include all chlorates (ClO4), sulphates (SO42), all Chlorides (Cl-) except AgCl, HgCl2 and PbCl2. All sulphates are soluble except CaSO4, BaSO4, PbSO4 and SrSO4.
Furthermore, some solutes can remain in suspension or appear as colloids and do not dissolve properly. Therefore, to have them dissolved evenly to separate the components, the suspension is poured in to an instrument like a test tube. Then the test tube is placed in a holder of a centrifuge and the knob is turned or spun until the colloids are thoroughly mixed and then left to settle. After some minutes or hours, the mixture is taken to separate the parts. It can be seen that the coarser
materials settle to the bottom. The medium sized particles are in the intermediate layers while the very fine grained are at the very top layer. Even the lightest particle can be seen to float at the surface layer. Careful decantation method can be used to separate the layers of their constituent parts.
My Prayer for PNG today is: “Could the Lord ever leave you. Could the Lord forget His Love. He will not leave you orphaned. He will not forget His love.”
Next week: Chemical bonding and metallic bonding

• Michael Uglo is the author of the science textbook “Science in PNG, Pacific, Asia and Caribbean” and a lecturer in Avionics, Auto- Piloting and Aircraft Engineering. Please send comments to: [email protected]