Category Chemistry

Ordinary soap has little value as an antiseptic and it does not kill or inhibit many types of bacteria.

However, the important function of washing one’s hands with soap is the mechanical removal of bacteria through scrubbing.

 The skin normally contains dead cells, dried sweat, bacteria, oily secretions and dust. In addition, having been to the toilet one would probably have contaminated his hands with faecal bacteria.

 Soap emulsifies the mixture of all these and the water washes it away. Because soaps are good for physically removing bacteria from the skin it is important to wash the hands before eating and after going to the toilet.

This prevents the transfer of potentially harmful bacteria by the faecal to oral route.

Cosmetic soaps contain antimicrobial compounds that strongly inhibit gram-positive bacteria and these are used to decrease body odour by preventing microbial growth on body secretions. These are non-household soaps that do contain some type of antibacterial compound.

These compounds act as disinfectants and kill bacteria. Of course, during our everyday activities we do not need or want to completely disinfect or sterilize our skin because the normal population of bacteria on us acts as a barrier against infection by pathogens. Healthy skin is a bacterial battleground populated with friendly bugs. These eat our sweat and, defend our skin from less friendly bugs that would not only eat our sweat but us as well.

Staphylococcus aureus is a typical invader that causes pimples and boils (or worse) when it beats our defenses. When we wash, we not only remove dirt and invasive bacteria, we also release a tide of friendly bugs from pores to recoat our skin for protection. This is fine unless you work in food preparation, you will then be required to use soaps that contain broad spectrum bactericides that kill all types of bacteria indiscriminately. Effective hand washing depends on many factors – the soap or cleaning agent, running water, clean towel or air drier for drying and on good technique.

Normal hand soap can remove germs, if used properly, and left to drain and dry between uses, not left sitting in a puddle of soggy soap and stagnant water. Pump dispensers are generally better than soap bars. Water must be clean and taps must not be contaminated by dirty hands – that is why hospital sink taps have elbow levers or, more rarely, foot pedals.

 Effective rinsing and drying, to remove any contaminated water without adding further contamination from a damp towel, are vital components of proper hand washing technique. This is why disposable paper towels are usually used in hospitals. Studies on hand-washing techniques by nurses have shown that some areas of the hand are less well-cleaned than others – fingers and the web between thumb and first finger are commonly inadequately leaned.a

Zeolite is used in the purification (more correctly softening) of water. Water in some localities contains salts of Calcium, Magnesium and Iron present in the earth. Such water finds it ‘hard’ or difficult to lather with ordinary washing soaps. This is because these salts react with the sodium compounds in soap causing wastage.

Further when such hard water is used in boilers these salts form a coating on the wells. This could be seen even in household vessels in which we use to boil water. Zeolite is the common name for a complex compound Sodium Aluminum Silicate. When hard water is passed through filters containing Zeolite, the salts of Calcium and Magnesium get absorbed and Sodium salts are released in exchange. Special kinds of Zeolite based on Manganese salts could remove salts of iron also if present in water.

 When the softening power of Zeolite gets weakened by constant use, it could be revived by pouring solutions of common salt and Potassium permanganate.

Water contains dissolved salts of calcium, magnesium and often iron in the form of bicarbonates, chlorides and sulphates present in the Earth’s crust. When such water is heated, the bicarbonates of calcium and magnesium decompose evolving carbon dioxide and leave behind sparingly soluble carbonates.

Bicarbonate of iron interacts with the carbon dioxide and water forming sparingly soluble ferric hydroxide (brown). These sparingly soluble salts form the layer or ‘scales’ seen in utensils and boilers.

In filters, there is no boiling, still similar chemical changes take place, though to a much less extent, when the remnants of water dry up. Chlorides and sulphates do not undergo these chemical changes, but form residues due to evaporation of the water.

The usual way to avoid this trouble is by using de-mineralized water, that is, ordinary water filtered through permutit (sodium aluminum silicate), manganese salts (to remove iron) and modern ion-exchange resins. The last one frees water from all mineral salts.

All these filters naturally get clogged when in continuous use but can be regenerated in most cases by simple chemical treatment.

Potassium cyanide when consumed causes death by gradually arresting the supply of oxygen to our body cells by forming stable complexes with hemoglobin (present in the blood) and cytochrome (a protein which helps in the respiration of the cells) and depriving them of their capacity to transport or exchange oxygen.

Normally, oxygen is carried to different parts of the body from the lungs by the blood using hemoglobin -the iron-containing, oxygen-carrying molecule of the red blood cells.

Hemoglobin is made up of a globular protein and four heme groups. The iron (in ferrous state) present in these heme complexes can bond to either an oxygen molecule or a water molecule or exchange them one for the other without much difficulty. It is because of this ability to exchange them, hemoglobin is able to pick up oxygen from the lungs, carry it to the body cells and bring back water in return.

The body cells ‘respire’ oxygen with the help of Myoglobin (hemoglobin like proteins present in the cells) and cytochrome (which function as electron carrier). One form of this cytochrome and hemoglobin are responsible for the sudden death due to cyanide poisoning.

When potassium cyanide is consumed, it splits into a potassium ion and a cyanide ion. The cyanide ion has a strong affinity to the ferrous ion than what oxygen has. As a result it occupies the site meant for oxygen in the hemoglobin. This process is irreversible and so it prevents transfer of oxygen.

Also, one form of cytochrome, designated as cytochrome-a, also binds with the cyanide ion and stabilizes the iron to such an extent that it does not take part in the electron transfer to the cell. This prevents oxygen in take by the cell. The symptoms of cyanide poisoning are giddiness, headache and bluish tinge of the skin. All these are indicators of lack of oxygen supply to various parts of the body. If not treated immediately, unconsciousness and death will follow.

Inhalation of amyl nitrate or injection of sodium nitrite to oxidize some of the hemoglobin to methymoglobin provides relief. Methymoglobin binds to cyanide ion more tightly than hemoglobin or cytochrome-a and helps in the removal of cyanide from the system. Carbon monoxide (CO) also has a similar effect when inhaled. It forms a stable compound called carboxy hemoglobin and deprives it of its oxygen carrying capacity. 

Formation of a solution is a physico-chemical process. When two substances mix to form a solution, heat is either absorbed (endothermic process) or released (exothermic process). This depends on various interactions taking place between the solvent and the solute at the molecular level.

 Glucose exists in the crystalline form. When dissolved in water, the crystal structure is broken. To break the bonds in the crystal energy is required. This is obtained from the water itself and so its temperature is reduced. Chemists call this an endothermic process. But considering a similar reaction, the dissolution of salt (sodium chloride) in water.

Though this is also an endothermic process the heat transfer involved is very less. (Moreover there are other interactions of the sodium and chloride ions with water, which are exothermic in nature).

Strong exothermic effects are observed in certain cases where the substances interact strongly with water molecules. For example, dissolution of washing soda (sodium carbonate) or sodium hydroxide. 

Fire involves a chemical reaction between fuel and atmospheric oxygen.  Once initiated it is self-sustaining, generates high temperatures and release a combination of heat, light, noxious gases and particulate matter.

The visible flame is the region in which this chemical process occurs and so flame is essentially a gas phase phenomenon. For flaming combustion to occur, solid and liquid fuels must be converted into gaseous form.

 For liquid fuels this is achieved by evaporative boiling. For solid fuels, the solid is chemically decomposed through the process of paralysis to generate volatile gases.

A flame is a region containing very hot atoms. At high enough temperatures all atoms will emit energy in the form of light as their electrons, which have been prompted to higher energy levels by absorbing heat energy, fall to lower energy states. Because this light is emitted in discrete quanta according to the relationship E= hf (where E=energy, h=Planck’s constant and f= frequency), flame colour is related to the magnitude of the energy quantum which is transformed to light.

This can most easily be seen with a Bunsen burner. A Bunsen burner that has a choked air supply burns cool, the light emissions from carbon atoms are relatively low in energy and appear more red or orange.

However, when the Bunsen is allowed air so that combustion is complete, the flame is hotter and the light emitted is of a higher energy and frequency and appears blue.

The luminescence of a flame is only of the story. The structure of the flame region is important to understand too. The flame area in a normal combustion environment, such as an open-air bonfire, is structured by convention currents which form as hotter, lighter air rises and allows cooler fresh air to replace it.

It is this channeling effect and movement of air that shapes the dancing flames. It is interesting that in space, in zero gravity, the hotter and cooler air cannot move by convection, so flames take on weird shapes and may be stifled by their own combustion products.