Gold, pure substance

A homogeneous mixture of two or more components, whether solid, liquid, or gaseous, is called a solution. Solutions have variable composition while pure substances do not. That is, the relative amounts of the various components in a solution can vary. Thus, air, salt water, and sixteen carat gold are each solutions. The gemstone, ruby, is also a solution since it consists of the mineral corundum (AI2O3) with some of the aluminum replaced by chromium to give the crystal its characteristic color. Since the amount of chromium present can be varied, ruby is a solution. 

Anyhow, at 25 °C, an ideal gas at 1 atm is 0.041 M. Condensed matter with small molecules (or metals such as silver and gold) can be up to 100 M. Hence, at their boiling points, most substances show an activity coefficient in the gaseous state (comparing with the molarity of the condensed matter and not the conventional activity a = 1 of pure substances) of the order of magnitude 1000. In view of the almost ideal nature of the gaseous state, it would perhaps be more appropriate to say that the condensed matter has/ 10 3 relative to the vapour at 1 atm. 

A pure substance has a definite composition, which stays the same in response to physical changes. A lump of copper is a pure substance. Water (with nothing dissolved in it) is also a pure substance. Diamond, carbon dioxide, gold, oxygen, and aluminum are pure substances, too. 

Pure substances are elements and compounds. They have only one type of particle in their structure. For example, pure water only contains water molecules, and gold solely gold atoms (Figure 2). 

A homogeneous crystalline material is not necessarily a pure substance. Thus natural crystals of sulfur are sometimes deep yellow or brown in color, instead of light yellow. They contain some selenium, distributed at random throughout the crystals in place of some of the sulfur, the crystals being fiomogeneous. and with faces as well formed as those for pure sulfur. These crystals are a crystalline solution (or solid solution). The gold-copper alloy used in jew elry is another example of a crystalline solution. It is a homogeneous material, but its composition is variable. 

Sweetened tea and 14-karat gold are examples of homogeneous mixtures. In a homogeneous mixture, the pure substances are distributed uniformly throughout the mixture. Gasoline, syrup, and air are homogeneous mixtures. Their different components cannot be seen—not even using a microscope. 

Recall that earlier in this chapter you considered the diversity of your surroundings in terms of matter. Although the diversity is astounding, in reality all matter can be broken down into a relatively small number of basic building blocks called elements. An element is a pure substance that cannot be separated into simpler substances by physical or chemical means. On Earth, 91 elements occur naturally. Copper, oxygen, and gold are examples of naturally occurring elements. There are also several elements that do not exist naturally but have been developed by scientists. 

Every pure substance (pure gold, pure water, pure oxygen, etc.) is made up of minute particles called molecules, aU of them identical for a particular substance, so that every water molecule is like aU the other water molecules. The water molecules are also different from aU the molecules of oxygen or of any other... 

The term matter refers to all materials that make up the universe. Many thousands substance of distinct kinds of matter exist. A substance is a particular kind of matter with a definite, fixed composition. Sometimes known as pure substances, substances are either elements or compounds. Familiar examples of elements are copper, gold, and oxygen. Familiar compounds are salt, sugar, and water. We ll discuss elements and compounds in more detail in Chapter 3. 

Classify each of the following as a pure substance, a solu-CQ tion, or a heterogeneous mixture a gold coin a cup of... 

From these and numerous other examples it follows that Graham s classification relates to mixtures rather than to chemically pure substances. A discussion of colloids from this point of view would have to do not with pure substances and their properties, but rather with those mixtures of substances which have colloidal properties. Ordinary chemical terminology also justifies this standpoint in that by colloidal silicic acid, gold, or platinum, for example, we understand not... 

By the 2000s BCE, these early civilizations had begun to distinguish the differences among pure substances that today we would call elements. The elements known to ancient peoples were carbon, iron, copper, silver, gold, mercury, sulfur, tin, lead, and antimony. 

Just from appearance alone, it may not be obvious whether something is a pure substance or a mixture. Air and pond water look like pure substances, but they are mixtures. Nor may it be obvious whether something is an element or a compound. Gold is an element but fool s gold is a compound composed of iron and sulfur, and is completely unrelated chemically to gold. 

To understand this the reader must recall that Philalethes earlier said that the alchemical elixir was simply gold digested to the highest degree, and that this was a homogeneous, spiritual substance. This meant that the particles of gold had been reduced to a smallness like that of fire particles, and because all impurity had been removed, all these minute particles were of the same size, that is, homogeneous. It is because of this uniformly minute character of the elixir s particles that it can penetrate into base metals per minima, that is, between the smallest particles of the base metals. Once the particles of elixir have entered into the internal structure of the base metals, their affinity with the pure metallic substance within the base metal allows them to mix with it. They are after all materially identical with this pure substance, and they are particles of the same size. 

A mixture is a combination of two or more substances [Figure 1.6(d)] in which the substances retain their distinct identities. Like pure substances, mixtures can be sohds, liquids, or gases. Some familiar examples are mixed nuts, 14-caiat gold, apple juice, milk, and air. Mixtures do not have a universal constant composition. Therefore, samples of air collected in different locations will differ in composition because of differences in altitude, pollution, and other factors. Various brands of apple juice may differ in composition because of the use of different varieties of apples, or there may be differences in processing and packaging, and so on. 

Pure substances are classified into two categories—elements and compounds. An element is a substance that cannot be separated into simpler substances. Oxygen, carbon, sulfur, aluminum, iron, and gold are elements. More than 110 elements are known, but only 91 occur naturally on Earth. The remainder have been created by scientists. 

Every pure liquid or solid has a characteristic density that helps distinguish it from other substances. To give one example, the density of pure gold is 19.3 g/cm, whether the sample is a nugget in a miner s pan or an ingot in a bank vault. Pyrite, an iron compound that resembles gold, has a much lower density of 5.0 g/cm. Table Ud lists... 

We call a substance that is made up of just one type of atom an element. Pure gold, for example, only has one type of atom. There are 92 different kinds of atoms, or elements, that occur naturally. All matter, from the smallest speck to the largest star, is made of these elements. 

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