| In fact all matter on Earth is made of chemical | | | | for other purposes utilize different ratios and often |
| substances and every material thing is a chemical or a | | | | include other oxides. Well-known examples are Pyrex |
| mixture of chemicals. Our home is a virtual chemistry | | | | glass, which includes 12.5% boron-oxide; lead crystal, |
| laboratory of fascinating products derived from raw | | | | which contains typically 16% PbO: and stained glass, |
| materials such as the water, soil, rock, etc found in | | | | which contains various elements selected from the |
| the biosphere of our planet. If we just scratch the | | | | transition elements from Ti to Cu, depending on the |
| surface of all the hundreds of chemical substances | | | | desired color. |
| used in every home, it will open our eyes to the | | | | Â |
| importance of chemical synthesis, engineering, | | | | Â Though nails aren't very high-tech materials, |
| manufacturing, and distribution of the substances | | | | we all know how necessary they are not only for |
| used in our everyday life. Our homes, apartments, | | | | successful constructions bur also a number of |
| schools, offices, parks, rails, cars, buses, airplanes and | | | | purposes. Most nails are made of steel, which is an |
| subways all these are our' home' at one time or | | | | alloy containing mostly iron and carbon. Nails that are |
| another as these are all just small parts of the home | | | | never expected to be in contact with water are plain |
| that we all share of our one, real home, the | | | | steel, but nails used in installing shingles or external |
| "Spaceship Earth" and through our study of | | | | panels must be made resistant to rust. To prevent |
| chemistry, together we appreciate how that one | | | | their rusting, steel nails are often galvanized. This |
| precious home is truly a "World of Chemistry, a | | | | means that they are coated with zinc, a good |
| World of Choices". | | | | reducing agent so that rather than the iron being |
| Wood is mostly cellulose with the smaller amounts of | | | | oxidized, the zinc will oxidize and the steel will not |
| hemicelluloses and lignin. All of these compounds are | | | | rust. Since zinc melts at a temperature (4190C) much |
| synthesized to be the structural parts of trees and | | | | below the melting point of iron (15350C), steel nails |
| are made via photosynthesis from carbon dioxide and | | | | can simply be dipped into molten zinc, removed, and |
| water. Cellulose is simply glucose molecules linked | | | | cooled. |
| together in the beta form to make long-chain | | | | Another option for rustles nails is to use aluminum |
| molecules. Hemi cellulose differs from cellulose in that | | | | instead of steel. There is a crucial difference between |
| the sugar molecules of which it is composed contain | | | | the products formed when iron and aluminum react |
| only five carbon atoms rather than six, the missing | | | | with oxygen. While iron forms the characteristic red |
| carbon atom being the one that is not part of the six | | | | rust, Fe2O3, which flakes off and allows more iron to |
| membered rings. Lignin is very different; it is a | | | | contact the air, aluminum also forms its oxide, Al2O3, |
| polymer of several aromatic alcohols such as conifer | | | | but this oxide adheres tightly to the metal and |
| alcohol and vanillin. | | | | prevents oxygen from reaching the rest of the |
| Glass is an amorphous mixture of the oxides of | | | | metal. Aluminum is not as strong as steel so is seldom |
| Silicon (SiO2), Calcium oxide (CaO) and sodium oxide | | | | used for structural purposes. However, besides being |
| (Na2O). We know that mixtures are not compounds | | | | light weight, it is valuable for adding to decoration. |
| because the composition of a mixture is not fixed, | | | | Â |
| but rather can vary over wide ranges. White sand is | | | | People often speak of cement and concrete as if |
| nearly pure SiO2 and is used directly in glass | | | | they were the same thing, but they are actually |
| manufacturing whereas sodium and calcium oxides | | | | different substances. Concrete is the substance we |
| are formed by heating sodium carbonate and calcium | | | | drive on and it is made from cement, sand or gravel |
| carbonate, respectively | | | | and water. The mixing of these three ingredients is |
| Na2CO3 Â Â Â Â | | | | done shortly before the wet concrete is put in place |
| Â Â Â Â Â | | | | to harden. Cement on the other hand, is made by |
| Â Â Â Â Â | | | | heating clay (typically Al2O3 .2SiO2. 2H2O) and |
| Â Â Â Â Â | | | | limestone (CaCO3) until they begin to melt at about |
| Â Â Â Â Â | | | | 12600C. This melt is called clinker and is then cooled |
| Â Na2O + CO2 | | | | and powdered to form what is sold commercially as |
| CaCO3Â Â Â Â Â | | | | Portland cement. Although cement is not a pure |
| Â Â Â Â Â | | | | compound, a typical clinker compound is Ca3SiO5, |
| Â Â Â Â Â | | | | which is more clearly written as 3CaO .SiO2. |
| Â Â Â Â Â | | | | We may believe it or not, even though concrete and |
| Â Â Â Â Â | | | | cement have been used for millennia, there is still |
| Â Â CaO + CO2 | | | | disagreement about what exactly happens when a |
| These ingredients are heated together until they all | | | | mixture of sand, water, and Portland cement is |
| melt and dissolve together. The mixture is then | | | | allowed to set and harden. It is clear that the water |
| cooled slowly until the glass stiffens, it does not | | | | reacts with CaO and Al2O3 to make Ca(OH)2 and |
| crystallize, so it is often spoken of as a super-cooled | | | | Al(OH)3 which react with calcium silicates to form |
| liquid rather than as a solid. In ordinary window glass, | | | | calcium aluminosilicate crystals, which interlock with |
| the mole ratio of the oxides is about 1.6 moles of | | | | each other. Concrete sets in a matter of hours and |
| Na2O to 1.0 moles of CaO to 6 moles of SiO2. Glass | | | | then continues to harden for years. |