Metric system standard mass

Scientists measure many different quantities—length, volume, mass (weight), electric current, temperature, pressure, force, magnetic field intensity, radioactivity, and many others. The metric system and its recent extension, Systeme International d Unites (SI), were devised to make measurements and calculations as simple as possible. In this chapter, length, area, volume, and mass will be introduced. Temperature will be introduced in Sec. 2.7 and used extensively in Chap. 11. The quantities to be discussed here are presented in Table 2-1. Their units, abbreviations of the quantities and units, and the legal standards for the quantities are also included. 

The metric system, or Systeme International d Unites (SI system as it is commonly known), is the predominant system of measurement in the world. In fact, the United States is one of only about three countries that do not commonly use the metric system. The metric system attempts to eliminate odd and often difircult-to-remember conversions for measurements (5,280 feet in a mile, for example). It is a decimal-based system with standard terminology for measurements of length, volume, and mass (weight). It also uses standard prefixes to measure multiples of the standard units. 

The metric system consists of a base unit and (sometimes) a prefix multiplier. Most scientists and healthcare providers use the metric system, and you are probably familiar with the common base units and prefix multipliers. The base units describe the type of quantity measured length, mass, or time. The SI system is sometimes called the MKS (meter, kilogram, second) system, because these are the standard units of length, mass, and time upon which derived quantities, such as energy, pressure, and force, are based. An older system is called the CGS (centimeter, gram, second) system. The derived CGS units are becoming extinct. Therefore, we will focus on the MKS units. 

Mass measurements of objects are carried out with the laboratory balance. Many types of balances are available for laboratory use. The proper choice of a balance depends upon what degree of accuracy is needed for a measurement. The standard units of mass are the kilogram (kg) in the SI system and the gram (g) in the metric system. Some conversion factors are listed below. 

As stated earlier, the primary unit of mass in the metric system is the gram. Because the gram is so small, however, the standard mass in SI and the legal standard in the United States is the kilogram. 

The mass df an object is measured in terms of grams (g) or kilograms (kg), the kilogram being equal to 1000 g. The kilogram is defined as the mass of a standard object made of a platinum-iridium alloy and kept in Paris. One pound is equal approximately to 454 g, and hence 1 kg is equal to approximately 2.2 lb. Note that it has become customary in recent years for the abbreviations of units in the metric system to be written without periods. 

Minutes are permitted to remain in the metric system for convenience or for historical reasons, even though they don t conform strictly to the rules. The minute, hour, and day, for example, are so customary that they re still defined in the metric system as 60 seconds, 60 minutes, and 24 hours— not as multiples of ten. For volume, the most common metric unit is not the cubic meter, which is generally too big to be useful in commerce, but the liter, which is one thousandth of a cubic meter. For even smaller volumes, the milliliter, one thousandth of a liter, is commonly used. And for large masses, the metric ton is often used instead of the kilogram. A metric ton (often spelled tonne in other countries) is 1,000 kilograms. Because a kilogram is about 2.2 pounds, a metric ton is about 2,200 pounds 10% heavier than an American ton of 2,000 pounds. Another often-used, non-standard metric unit is the hectare for land area. A hectare is 10,000 square meters and is equivalent to 0.4047 acre. 

The recent popularity of chromatographic systems with mass spectro-metric detection is a result of the evolution and development of small, relatively inexpensive instruments that are capable of obtaining information about compounds in a stream of FIPLC eluent using standard, rugged,... 

The exact value of the atomic mass unit is defined in relation to a standard, just as the units of the metric system represent defined quantities. The carbon-12 isotope has been chosen and is assigned a mass of exactly 12 atomic mass units. Hence this standard reference point defines an atomic mass unit as exactly one-twelfth the mass of a carbon-12 atom. 

The need for common units also applies to scientists, who measure quantities such as mass, length, time, and temperature. If every scientist had her or his own personal set of units, complete chaos would result. Unfortunately, although standard systems of units did arise, different systems were adopted in different parts of the world. The two most widely used systems are the English system used in the United States and the metric system used in most of the rest of the industrialized world. 

Science progressed more rapidly in the last 200 years than it had in the few thousand years previous. A great deal of this success came from the agreement among scientist to create and use a set of standard conventions. The two most important conventions are the periodic table and the international system of units, called SI units. SI units are based on the metric system, and it s more common to see temperature expressed as Celsius than Fahrenheit. And you see lengths expressed in meters instead of inches and feet. Weights and mass are expressed in terms of grams instead of pounds or stone. 

The metric system, or International System (SI, from Systlme International), is a decimal system of units for measurements of mass, length, time, and other physical quantities. Built around a set of standard units, the metric system uses factors of 10 to express larger or smaller numbers of these units. To express quantities that are larger or smaller than the standard units, prefixes are added to the names of the units. These prefixes represent multiples of 10, making the metric system a decimal system of measurements. Table 2.1 shows the names, symbols, and numerical values of the common prefixes. Some examples of the more commonly used prefixes are... 

The standard unit for mass in the metric system is the kilogram. In chemistry we often use the gram instead, as we tend to work in smaller quantities. 

The standard masses (standard weights) in the metric system are calibrated (checked) by comparison with the standard kilogram in Paris (Appendix I). The IS unit of mass is the kilogram. The abbreviation for gram is g, and for kilogram kg (1 kg = 1000 g). 

The Quantification of Mepyramine Using an Homologous Internal Standard Plus a Deuterated Carrier with a Gas Chromatographic-Mass Spectro-metric System Operating in Single Ion Detection Mode Adv. Mass Spectrom. 7B 1551-1554 (1978) CA 89 99525x... 

By the late 1860s, even better metric standards were needed to keep pace with scientific advances. In 1875, the Treaty of the Meter international treaty set up well-defined metric standards for length and mass, and established permanent machinery to recommend and adopt further refinements in the metric system. This treaty, known as the Metric Convention, was signed by 17 countries, including the United States. 

In Section 2.6.1, we note that the density of liquids changes with temperature, decreasing with increasing temperature (as the volume expands) and increasing with decreasing temperature (as the volume contracts). The density of water is equal to 1.000 g/mL at 4°C, a temperature that is near the freezing point of water. The link between the mass and volume domains then is that 1 g of water is the same as 1 mL of water at 4°C. Again, this shows the creativity and convenience that is exhibited by the metric system. Water has been used as a standard substance to create links and to set-up entire domains of measurement in the metric system. 

The mass of an object is a measure of the quantity of material it contains. The SI unit of mass, the kilogram (kg), is used for larger masses, such as body mass. The standard for mass, the international prototype kilogram (IPK), is a cylinder that is made of a platinum-iridium alloy. In the metric system, the unit for mass is the gram (g), which is used for smaller masses. There are 1000 g in one kilogram. In comparison to the U.S. system, the mass of 1 kg is equivalent to 2.205 lb, and 453.6 g is equal to one pound. Some useful relationships between different units for mass follow ... 

The thickness of wire often is measured using a system called the American Wire Gauge (AWG) standard. The smaller the gauge number, the larger the diameter of the wire. For example, 18-gauge copper wire has a diameter of about 0.102 cm 12-gauge copper wire has a diameter of about 0.205 cm. Such small diameters are difficult to measure accurately with a metric ruler. In this experiment, you will plot measurements of mass and volume to find the density of copper. Then, you will use the density of copper to confirm the gauge of copper wire. 

The base unit of mass in the International System of Units (SI see discnssion in Appendix B) is the kilogram (kg), but it is inconveniently large for most practical pnrposes in chemistry. The gram often is used instead moreover, it is the standard nnit for molar masses. Several units for volume are in frequent use. The base SI unit of the cnbic meter (m ) is also unwieldy for laboratory purposes (1 m water weighs 1000 kg, or 1 metric ton). We will, therefore, nse the liter (1 L = 10 m ) and the cubic centimeter, which is identical to the milliliter... 

The IR detection of evolved gases opens new possibilities in the quantification of thermogravi-metric analysis. Besides measuring the mass loss of a TG step, the total amount can also be calculated after calibration of a. single component and integration over time [128], A further improvement in quantitative TG/FT-IR is achieved by PulseTA [ 129], Here, a certain amount of gas or liquid is injected into the system and used as internal calibration standard for the quantification of the unknown amount of evolved gas. 

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