Systems of Measurement
Systems of Measurement
Chemistry is an experimental science that involves measurement of the magnitude of various properties of substances. Measurements generate numbers, and we need units attached to these numbers so we can tell what exactly is being measured. Some examples of quantities measured include amount, mass, pressure, size, temperature, time, volume, etc. There are several systems of units, for example, the English system and the metric system. The metric system is the most commonly used system of measurement in chemistry. In 1960, a modernized version of the metric system known as the Systeme Internationale (or SI system) was recommended for worldwide adoption. The SI, based on the metric system, consists of seven fundamental units and several units derived from them. These units serve all scientific measurements. The seven fundamental units are listed in table 2-1. The fundamental units do have some shortcomings. For example, in some cases the base unit is inconveniently large or small. To overcome this, the SI units can be modified through the use of prefixes. The prefixes define multiples or fractions of the base or fundamental units. Some examples are listed in table 2-2. Mass, length, and time are important quantities commonly measured in science, which are assigned fundamental units. The standard unit of mass in the SI is the kilogram (kg), which is defined as the mass of a certain block of platinum–iridium alloy, also known as the prototype kilogram, kept in a vault at the International Bureau of Weights and Measures, in Sevres, France. Other mass units that are related to the kilogram include gram (g), milligram (mg), and microgram (μg). Here is how they are related: 1000 g = 1 kg 1000 mg = 1 g 1,000,000 μg = 1 g Note that the symbol for grams is g, not gm, gms, gr, or anything else. The SI unit of length is the meter (m), which is defined as the distance light travels in approximately 1/299,792,458 second.
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