The Units of Measurement

A FIGURE 1.11 Using Chemical Energy to Do Work The compounds produced when gasoline bums have less chemical potential energy than the gasoline molecules. 

In 1999, NASA lost the 125 million Mars Climate Orbiter. The chairman of the conunis-sion that investigated the disaster concluded, The root cause of the loss of the spacecraft was a failed translation of English units into metric units. As a result, the orbiter—which was supposed to monitor weather on Mars—descended too far into the Martian atmosphere and burned up. In chemistry as in space exploration, units—standard quantities used to specify measurements— are critical. If we get them wrong, the consequences can be disastrous. 

The two most common unit systems are the metric system, used in most of the world, and the English system, used in the United States. Scientists use the International System of Units (SI), which is based on the metric system. 

A The 125 million Mars Climate Orbiter was lost in the Martian atmosphere in 1999 because two groups of engineers failed to communicate to each other the units that they used in their calculations. 

I The abbreviation St comes from the French, I Systeme Intenatiottal d Unltis. 

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The determination of equilibria is done theoretically via the calculation of free energies. In practice, the concept of fugacity is used for which the unit of measurement is the bar. The equation linking the fugacity to the free energy is written as follows >... 

Imagine that you find the following instructions in a laboratory procedure Transfer 1.5 of your sample to a 100 volumetric flask, and dilute to volume. How do you do this Clearly these instructions are incomplete since the units of measurement are not stated. Compare this with a complete instruction Transfer 1.5 g of your sample to a 100-mL volumetric flask, and dilute to volume. This is an instruction that you can easily follow. 

To understand permeabiUty or barrier property values, it is necessary to define the units of measure. These units are compHcated and many different sets of units are ia common use. Furthermore, from time to time the units of permeabiUty are presented ia confused or iacorrect fashion ia the Hterature. 

Select the units of measurement for iaput data and output reports. 

To express the quantity of energt available in the lit]iiid entering into the pump, the unit of measure for NPSH is feet of head or elevation in the pump suction. The pump has its NPSHr, or Net Positive Suction Head Required. The system, meaning all pipe, tanks and connections on the suction side of the pump has the NPSHa, or the Net Positive Suction Head Available. There should always be more NPSHa in the system dian the NPSHr of the pump. Let s look at them, beginning with what the pump recgiires ... 

Micrometer a unit of length equal to one millionth of a meter the unit of measure for particle size. 

Systematic error, as stated above, can be eliminated— not totally, but usually to a sufficient degree. This elimination process is called calibration. Calibration is simply a procedure where the result of measurement recorded by an instrument is compared with the measurement result of a standard. A standard is a measuring device intended to define, to represent physically, to conserve, or to reproduce the unit of measurement in order to transmit it to other measuring instruments by comparison. There are several categories of standards, but, simplifying a little, a standard is an instrument with a very high accuracy and can for that reason be... 

Rem (Rbntgen equivalent man) The unit of measure of the radiation dose to the internal tissues. 

Importance also applies to what may appear minor decisions in the planning or design phase. If such decisions are incorrect they could result in major problems downstream. If not detected, getting the decimal place wrong or the units of measure wrong can have severe consequences. Audits should verify that the appropriate controls are in place to detect such errors before it is too late. 

As illustrated in Figure 43.11, the peak-to-peak amplitude (2A, where A is the zero-to-peak) reflects the total amplitude generated by a machine, a group of components, or one of its components. This depends on whether the data gathered is broadband, narrowband, or component. The unit of measurement is useful when the analyst needs to know the total displacement or maximum energy produced by the machine s vibration profile. 

Cholesterol in blood is measured in milligrams of cholesterol per deciliter of blood. If the unit of measurement were changed to grams of cholesterol per milliliter of blood, what would a cholesterol reading of 185 mg/dL translate to ... 

The units of weight in the apotiiecaries system are grains, drams, and ounces. The units of volume are minims, fluid drams, and fluid ounces. The units of measurement in this system are not based on exact measurements. 

Step 1. As above, begin by writing the unit of measure to be calculated, followed by an equal sign. 

Repeat Steps 3 and 4. Continue with the equation by placing die next fraction beginning with the unit of measure of die denominator of the previous fraction. 

Melvin Mooney devised an instrument to measure the stiffness of uncured compounds, also known as the compound s viscosity. The unit of measurement is expressed in Mooney units. Figure 28.1 shows an instrument set up for measuring viscosity, the Mooney viscometer, in which a knurled knob (rotor) rotates (at 2 revolutions per minute) in a closed heated cavity filled with rubber [2]. 

The units associated with a numericai vaiue are just as important as the vaiue itself. If a recipe instruction reads, Add 1 of sugar, that instruction is useless. The unit of measure, such as teaspoon, must also be included. It is essential to include a unit with every experimental value. 

Unlike the case of a surface reaction, there is no need to specify the units of measurement because all reacting species are in the three-dimensional space of the reaction medium, and all relevant rates are in concentration per unit of time. The unknown concentration of the unoccupied enzymes follows by assuming that the reaction is at steady state ... 

Absolute temperature The lowest possible temperature is absolute zero. The absolute temperature scale starts there and increases in increments of 1 degree Celsius. The unit of measurement is the kelvin (K). 

The use of standardized data (variable standardization or column autoscaling, see Frank and Todeschini [1994]) results in data which are independent of the unit of measurement. Other types of standardization like object standardization, row autoscaling, or global standardization (global autoscaling, (xij — x)/s) do not play a large role in data analysis. 

Column headings on forms should always specify the units of measurement and other details of entries to be made. The form should he arranged so that sequential entries proceed down a page, not across. Each column should be clearly labeled with a heading that identifies what is to be entered in the column. Any fixed part of entries (such at °C) should be in the column header. 

An everyday task in our laboratories is to make measurements of some property as a function of one or more parameters and to express our data graphically, or more compactly as an algebraic equation. To understand the relationships that we are exploring, it is useful to express our data as quantities that do not change when the units of measurement change. This immediately enables us to scale the response. Let us take as an example the effect of temperature on reaction rate. The well-known Arrhenius equation gives us the variation... 

A quantitative report will state the amount of a particular substance present in the sample and it is important that the units of measurement are meaningful and appropriate in order to prevent subsequent misunderstandings. When reporting quantitative results it is desirable to indicate their reliability, a feature which can often be assessed statistically. In practice it may not be necessary to present this information with each report but it should be readily available for reference. 

Graphs produced for quantitative analytical purposes must be dated and include adequate information on the method of analysis, e.g. the SOP serial number, the analyte and the units of measurement. The scale of each axis should be carefully chosen and not simply fill the available space. 

Barrel the unit of measurement of liquids in the petroleum industry equivalent to 42 U.S. standard gallons or 33.6 imperial gallons. 

Alkalinity The concentration of negative charge in a solution that can be titrated by a strong acid. In seawater, HCO3 and contribute most of this negative charge. The units of measurement... 

Select the items to be analyzed Select the unit of measure for analysis Select the time period to be analyzed List the items in the order of decreasing magnitude... 

Construct two vertical axes. Tbe left scale should present the units of measures and the right one should be from 0% to 100%... 

Leave a space between a numeral and its unit of measure, unless the unit of measure is a percent sign (%) ... 

Rule 9 In a series or range with a span of three or more numerals, include the unit of measure only once. Use the en dash to mean to or through. (See The ACS Style Guide for additional information on when and where to use en dashes.)... 

The quantity of a gas can be indicated by way of its mass or its weight in the units of measure normally used for mass or weight. In practice, however, the product of p V is often more interesting in vacuum technology than the mass or weight of a quantity of gas. The value embraces an energy dimension and is specified in millibar liters (mbar I) (Equation 1.7). Where the nature of the gas and its temperature are known, it is possible to use Equation 1.7b to calculate the mass m for the quantity of gas on the basis of the product of p V ... 

This calculation in relation to both the hazard rate and the survival probabilities has been undertaken at intervals of one month. In practice we use intervals which correspond to the unit of measurement for the endpoint itself, usually days, in order to use the total amount of information available. 

Frequency The number of times a periodic wavelength cycle occurs in 1 s the unit of measurement is hertz (Hz). 

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