Homogeneous mixtures can be classified according to the size of their constituent particles as either solutions or colloids. Solutions, the most important class of homogeneous mixtures, contain particles with diameters in the range 0.1–2 nm the size of a typical ion or small molecule. They are transparent, although they may be colored, and they do not separate on standing. Colloids, such as milk and fog, contain particles with diameters in the range 2–500 nm. Although they are often murky or opaque to light, they do not separate on standing. Mixtures called suspensions also exist, having even larger particles than colloids. These are not truly homogeneous, however, because their particles separate on standing and are visible with a low-power microscope. Blood, paint, and aerosol sprays, are examples.
We usually think of a solution as a solid dissolved in a liquid or as a mixture of liquids, but there are many other kinds of solutions as well. In fact, any one state of matter can form a solution with any other state, and seven different kinds of solutions are possible. Even solutions of one solid with another and solutions of a gas in a solid are well known. Metal alloys, such as stainless steel (4–30% chromium in iron) and brass (10–40% zinc in copper) are solid/solid solutions, and hydrogen in palladium is a gas/solid solution. Metallic palladium, in fact, is able to absorb up to 935 times its own volume of H2 gas.
Kind of solution - Example
Gas in gas - Air (O2, N2, Ar, and other gases)
Gas in liquid - Carbonated water (CO2 in water)
Gas in solid - H2 in palladium metal
Liquid in liquid - Gasoline (mixture of hydrocarbons)
Liquid in solid - Dental amalgam (mercury in silver)
Solid in liquid - Seawater (NaCl and other salts in water)
Solid in solid - Metal alloys, such as sterling silver (92.5% Ag, 7.5% Cu)
For solutions in which a gas or solid is dissolved in a liquid, the dissolved substance is called the solute and the liquid is called the solvent. When one liquid is dissolved in another, the minor component is usually considered the solute and the major component is the solvent. Thus, ethyl alcohol is the solute and water the solvent in a mixture of 10% ethyl alcohol and 90% water, but water is the solute and ethyl alcohol the solvent in a mixture of 90% ethyl alcohol and 10% water.
transparent: trong suốt, trong sạch
opaque: mờ đục
suspension: huyền phù
truly: thật, thật sự
microscope: kính hiển vi
aerosol sprays: dạng bụi nước phun
stainless: không gỉ
brass: đồng thau
absorb: hấp thụ