Converting Concentration Units

This problem requires students to perform fundamental calculations of concentration, convert units from grams per liter to ppm, read and analyze a table of data, draw inferences from their calculations, and also to make decisions about their results. Such problems are important in the education of our students, because we want to foster this type of analytical and critical thinking towards real world problems. 

Mass Transfer Rates. Mass transfer occurs across the interface. The rate of mass transfer is proportional to the interfacial area and the concentration driving force. Suppose component A is being transferred from the gas to the liquid. The concentration of A in the gas phase is Ug and the concentration of A in the liquid phase is u . Both concentrations have units of moles per cubic meter however they are not directly comparable because they are in different phases. This fact makes mass transfer more difficult than heat transfer since the temperature is the temperature regardless of what phase it is measured in, and the driving force for heat transfer across an interface is just the temperature difference Tg—Ti. For mass transfer, the driving force is not Ug—ai. Instead, one of the concentrations must be converted to its equivalent value in the other phase. 

SI (le Systeme International d UniUs) units are used in many countries to express clinical laboratory and serum drug concentration data. Instead of employing units of mass (such as micrograms), the SI system uses moles (mol) to represent the amount of a substance. A molar solution contains 1 mol (the molecular weight of the substance in grams) of the solute in 1 L of solution. The following formula is used to convert units of mass to moles (mcg/mL to pmol/L or, by substitution of terms, mg/mL to mmol/L or ng/mL to nmol/L). 

Other common ways of expressing abundances, particularly of solid or liquid particles, is to express them as concentrations in units of micrograms per cubic meter or nanomoles per cubic meter. For purposes of consistency, concentrations expressed in these units should be normalized to standard conditions of temperature and pressure. Because there is some confusion as to what constitutes standard conditions in atmospheric chemistry (273 K and 1.013 bar are commonly used in chemistry and physics and 293 K and 1.013 bar are used in engineering), it is important to define the standard conditions that are assumed when reporting data. This explicit definition is frequently not done. Concentrations expressed in these units can be easily converted to mixing ratios by use of the ideal gas law ... 

The spectrophotometer measures and displays the increase in absorbance at 410 nm as a function of time (AA/At). Whether the output from the instrument is in the form of a strip chart or is collected by a computer, the reaction velocities are usually expressed in terms of change in concentration per unit time, or converted to specified units of enzyme activity. The International Unit (U) for enzyme activity is defined as the amount of enzyme that transforms 1 pmol substrate to product in 1 min under specified assay conditions. The SI unit for activity is the katal, which is defined as the amount of enzyme that transforms 1 mol substrate per second under specified conditions. Thus 1 U = 16.7 nkatal. To convert slopes AA/At values) to velocities (v), the following equation is used ... 

Strategy. Because we are given the flow into and out of the compartment (the Earth s atmosphere), we need to know the stock (M) so that we can divide one by the other and get a residence time (r = M/F). Although we do not know the stock, we do know the concentration of oxygen in the atmosphere (21%). Thus, to calculate the stock of oxygen in the Earth s atmosphere, it is convenient to use the volume of the atmosphere at 15°C and at 1 atm pressure, which we figured out above to be 4.3 x 1021 L, and to multiply that by the concentration. Then, we just have to convert units to calculate the mass of oxygen in kg. 

Throughout this chapter, the units used to express concentration or intake of uranium are the same units reported by the authors, and are sometimes followed by converted units using the conversion factor of 0.68 pCi/pg, or other multiplier based on the information provided about the isotopic mixture. In some cases, values are expressed in mass units while in other cases values are expressed as activities. In the case of natural uranium with a fixed abundance of the three isotopes, conversion from one unit to the... 

First, convert the sulfate concentration to units of grams per cubic centimeter ... 

The answer is b. (Murray, pp 48-73. Scriver, pp 4571-4636. Sack, pp 3-17. Wilson, pp 287-317.) Substrate concentrations are usually expressed in terms of molarity, e.g., M = moles per liter, mM = millimoles per liter, lM = micromoles per liter. K, , the Michaelis constant, is expressed in terms of substrate concentration. Each unit of enzyme activity is described as the amount of enzyme that converts a specific amount of substrate to a product within a given time. The standard units of activity are micromoles of substrate per minute. Specific activity relates the units of enzyme activ-... 

The infrared method for the estimation of the NCO groups decrease in the PU postcure processes has been used by many authors [333, 334]. In the case of our PUs, we have determined the decrease in NCO group absorbance of the IR spectrum at 2 290 cm on 20fi thin PU films cast from the reaction melt between two teflon sheets. The kinetic measurements started immediately after demolding. The films were maintained under the same maturation conditions as in the case of thicker sheets. These values have been converted into a NCO group equivalent concentrations per unit volume of polymer taking into account the measured absorbance and the polymer thickness. In every case, corrections for variation of thickness of PU films with time were made. The NCO group molar extinction coefficient was established on standard solutions of DBDI in benzene [17]. 

Nowadays all AA spectrometers have a readout in absorbance A and in converted units such as concentrations c and mass m, which are linearly proportional to A (see Sec. 1.1). Particularly in ETAAS, where the signals are proportional to the analyte mass, it has been found advantageous to measure the integrated absorbance A j t ... 

To convert this C2H6 concentration in ppm(v) into a NMHC concentration with units of ppmC, note that there are two moles of carbon per mole of C2H6 ... 

The units of concentration most frequently encountered in analytical chemistry are molarity, weight percent, volume percent, weight-to-volume percent, parts per million, and parts per billion. By recognizing the general definition of concentration given in equation 2.1, it is easy to convert between concentration units. 

The concentration of Pb + in the original sample of blood can be determined by making appropriate substitutions into equation 5.7 and solving for C. Note that all volumes must be in the same units, thus Vj is converted from 1.00 )J,L to 1.00 X 10-3 mb. 

Km for an enzymatic reaction are of significant interest in the study of cellular chemistry. From equation 13.19 we see that Vmax provides a means for determining the rate constant 2- For enzymes that follow the mechanism shown in reaction 13.15, 2 is equivalent to the enzyme s turnover number, kcat- The turnover number is the maximum number of substrate molecules converted to product by a single active site on the enzyme, per unit time. Thus, the turnover number provides a direct indication of the catalytic efficiency of an enzyme s active site. The Michaelis constant, Km, is significant because it provides an estimate of the substrate s intracellular concentration. 

The units of [77] reveal the concentration units in this experiment to be grams of protein per cubic centimer of solution. Dividing this concentration unit by the density of the unsolvated protein converts these concentration units to volume fractions ... 

The heat of hydration is approximately —70 kj /mol (—17 kcal/mol). This process usually produces no waste streams, but if the acrylonitrile feed contains other nitrile impurities, they will be converted to the corresponding amides. Another reaction that is prone to take place is the hydrolysis of acrylamide to acryhc acid and ammonia. However, this impurity can usually be kept at very low concentrations. American Cyanamid uses a similar process ia both the United States and Europe, which provides for their own needs and for sales to the merchant market. 

Worldwide primary aluminum capacity. Table 14 (35), continues to grow but mosdy in countdes where there is low cost electric power. Primary capacity in the United States, Table 15, has been reduced from 5,019 thousand metric tons in 1982 to 3,902 thousand metric tons in 1988. The United States and other developed countries are expected to concentrate mote on converting taw aluminum into high value added products. 

Friedel-Grafts Reaction. Until quite recently, the manufacture of anthraquiaone ia the United States was by the Friedel-Crafts reaction benzene [71-43-2] and phthaUc anhydride [85-44-9] condense ia the preseace of anhydrous aluminum chloride to give o-benzoylbenzoic acid [85-52-9] which, on treatment with concentrated sulfuric acid, is converted iato anthraquiaoae ia high yields and purity (33). 

The NAAQS are expressed ia the form of ground level concentrations (GLC), which are the concentrations of pollutant ia the ambient air as measured at ground level, ia units of either micrograms per cubic meter or ppm. In order to convert a source s emission ia kilograms per hour to a GLC, dispersion modeling must be used. 

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