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A homogeneous mixture , also called a solution , exhibits a uniform composition and appears visually the same throughout. An example of a solution is a sports drink, consisting of water, sugar, coloring, flavoring, and electrolytes mixed together uniformly ( [link] ). Each drop of a sports drink tastes the same because each drop contains the same amounts of water, sugar, and other components. Note that the composition of a sports drink can vary—it could be made with somewhat more or less sugar, flavoring, or other components, and still be a sports drink. Other examples of homogeneous mixtures include air, maple syrup, gasoline, and a solution of salt in water.
Although there are just over 100 elements, tens of millions of chemical compounds result from different combinations of these elements. Each compound has a specific composition and possesses definite chemical and physical properties by which we can distinguish it from all other compounds. And, of course, there are innumerable ways to combine elements and compounds to form different mixtures. A summary of how to distinguish between the various major classifications of matter is shown in ( [link] ).
Eleven elements make up about 99% of the earth’s crust and atmosphere ( [link] ). Oxygen constitutes nearly one-half and silicon about one-quarter of the total quantity of these elements. A majority of elements on earth are found in chemical combinations with other elements; about one-quarter of the elements are also found in the free state.
| Elemental Composition of Earth | ||||||
|---|---|---|---|---|---|---|
| Element | Symbol | Percent Mass | Element | Symbol | Percent Mass | |
| oxygen | O | 49.20 | chlorine | Cl | 0.19 | |
| silicon | Si | 25.67 | phosphorus | P | 0.11 | |
| aluminum | Al | 7.50 | manganese | Mn | 0.09 | |
| iron | Fe | 4.71 | carbon | C | 0.08 | |
| calcium | Ca | 3.39 | sulfur | S | 0.06 | |
| sodium | Na | 2.63 | barium | Ba | 0.04 | |
| potassium | K | 2.40 | nitrogen | N | 0.03 | |
| magnesium | Mg | 1.93 | fluorine | F | 0.03 | |
| hydrogen | H | 0.87 | strontium | Sr | 0.02 | |
| titanium | Ti | 0.58 | all others | - | 0.47 |
Water consists of the elements hydrogen and oxygen combined in a 2 to 1 ratio. Water can be broken down into hydrogen and oxygen gases by the addition of energy. One way to do this is with a battery or power supply, as shown in ( [link] ).
The breakdown of water involves a rearrangement of the atoms in water molecules into different molecules, each composed of two hydrogen atoms and two oxygen atoms, respectively. Two water molecules form one oxygen molecule and two hydrogen molecules. The representation for what occurs, will be explored in more depth in later chapters.
The two gases produced have distinctly different properties. Oxygen is not flammable but is required for combustion of a fuel, and hydrogen is highly flammable and a potent energy source. How might this knowledge be applied in our world? One application involves research into more fuel-efficient transportation. Fuel-cell vehicles (FCV) run on hydrogen instead of gasoline ( [link] ). They are more efficient than vehicles with internal combustion engines, are nonpolluting, and reduce greenhouse gas emissions, making us less dependent on fossil fuels. FCVs are not yet economically viable, however, and current hydrogen production depends on natural gas. If we can develop a process to economically decompose water, or produce hydrogen in another environmentally sound way, FCVs may be the way of the future.
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