Balance Reading

Plug flow reactor (PFR) with recycle. The recycle reactor is characterized by a non-zero value of R, that is the ratio between the mass flow rate of the recycled stream and the feeding rate Q. The material balance reads for this case as... 

The system to be solved involves five unknown concentrations which, for sake of illustration, are made equal to the corresponding activities. An identical number of equations must be found that include component conservation plus a number of mass action laws corresponding to the formation of as many species as the excess of species over components. We first write the recipe, i.e., the mass balance for the components, not including the components of water. Calcium mass balance reads... 

FIGURE 3.2 Displays of balances read (a) to the nearest gram, (b) to the nearest tenth of a gram, (c) to the nearest hundredth of a gram, (d) to the nearest milligram, (e) to the nearest tenth of a milligram, and (f) to the nearest hundredth of a milligram. 

Increasingly there is a need to evaluate simple physical properties such as solvent imbibition in a more rapid manner for high-throughput materials studies, or for real-time evaluation. Recently this issue has been addressed and a very elegant solution developed [75] based on earher work [76, 77]. In this a polypropylene disposable syringe containing a known mass of polymer is suspended from a microbalance and the balance reading set to zero. A reservoir of the solvent to be inves-... 

TG-FT-IR, Pyrolysis analyses were performed on the preliquefaction solids using thermogravimetric (TG) analysis with on-line analysis of the evolved products (including an infrared spectrum of the condensables) by FT-IR. The TG-FTIR method has been described previously (23-25). The Bomem TG/plus instrument was employed. A sample is continuously weighed while it is heated. A flow of helium sweeps the products into a multi-pass cell for FT-IR analysis. Quantitative analysis of up to 20 gas species is performed on line. Quantitation of the tar species is performed by comparison with the balance reading. 

Zalkowska and Piotrowska have reported a gravimetric method for the determination of procaine and other organic compounds by the Buerger method [92]. The accuracy of the gravimetric results for carbon and hydrogen were reported to depend on variation in the balance readings. 

Figure 2-5 shows buoyancy corrections for several substances. When you weigh water with a density of 1.00 g/mL, the true mass is 1.001 I g when the balance reads 1.000 0 g. The... 

Defect clustering is the result of defect interactions. Pair formation is the most common mode of clustering. Let us distinguish the following situations a) two point defects of the same sort form a defect pair (B + B = B2 = [B, B] V+V = V2 = [V, V]) and b) two different point defects form a defect pair (electronic defects can be included here). The main question concerns the (relative) concentration of pairs as a function of the independent thermodynamic variables (P, T, pk). Under isothermal, isobaric conditions and given a dilute solution of B impurities, the equilibrium condition for the pair formation reaction B + B = B2 is 2-pB = The mass balance reads NB + 2-NBi = NB, where NB denotes the overall B content in the matrix crystal. It follows, considering Eqns. (2.39) and (2.40), that... 

Assume that you take a flask, evacuate it to remove all the air, and find its mass to be 478.1 g. You then fill the flask with argon to a pressure of 2.15 atm and reweigh it. What would the balance read (in grams) if the flask has a volume of 7.35 L and the temperature is 20.0°C ... 

A schematic diagram of the experimental set-up is shown in Fig. 6.1. It employs a stainless steel rod of 0.5 cm diameter and length 3 cm. The rod is hung by a thread from under a standard bottom-loading balance (e.g., Shimadzu model EB-280) of sensitivity 1 mg. This balance rests on a platform that can be raised or lowered at speeds down to about 1.0 mm/min. On raising the rod, the balance reading increases steadily, reaches a maximum value (Wmax) and then falls. The maximum is approached slowly (i.e., over a period of approximately 10 sec for the last few mg) in order to obtain equilibrium measurements. From the value of Wmax the weight of the rod in air (W r0d) is subtracted, and the surface... 

The balance readings used to weigh out the samples should become a permanent record and should be retained as original raw data in the archives. 

The greater the accuracy of a balance, the closer the balance will read the nominal weight of a calibration weight. If the calibration weight reads 10 mg, the balance should read 10 mg. If, for example, the balance reads 10.5 mg, it has less than desirable accuracy, and if it reads 12 mg, it has poor accuracy. 

Precision. Does the balance read the same weight over a series of mea-... 

The balance is itself insensitive to pressure changes provided all its parts are at uniform temperature. However, when there is a temperature difference between the furnace and the balance, convection currents are set up which necessitate a buoyancy correction to the balance readings. This causes little difficulty since the readings can always be referred to the vacuum condition. 

Points 1 and 12 were assumed to correspond at their observed activities to the upper curve of run II, which had been evaluated as described in Improvements. The compositions so determined were used with the observed balance readings to establish the two calculation constants used in the evaluation of all other data in run I. Point 128 was confirmed within analytical error by a chemical analysis. The compositions associated with run III (Figure 2) could not be determined directly because of the unknown amount of oxide present. However, since the absolute composition-activity relationships for CeCd 6(4) are known approximately, an estimate of the composition was possible. The resulting calculated values for CeCd 4 5 were increased by 0.05%, in order to be consistent with the position of the upper structure in Figure 1. The resulting composition values should not be assumed to correspond precisely to those in Figure 1 however, it is not essential that the composition be known with greater precision. 

A manufacturer of a four-figure balance states that the balance reading is within +0.1 mg with 95% confidence. 

Note 3. Balance readings, burette readings and calculations should be included in the results section. 

The weight of an ignited precipitate is itself not necessarily represented accurately by the balance reading there may be equilibration of the precipitate and container with atmospheric moisture (the atmosphere in a desiccator probably is not dry), and absorption of carbon dioxide or ammonia. 

EXAMPLE 26-5 An examination of the last digit of buret and balance readings reported by students of introductory quantitative analysis during a practical examination gave the following results. 

Equation 15.60 has to be coupled with the R time dependency coming out from a mass balance made up on the tri-laminate, donor, and receiver compartments. This mass balance reads... 

Sources of random uncertainties in the calibration of a pipet include (1) visual judgments, such as the level of the water with respect to the marking on the pipet and the mercury level in the thermometer (2) variations in the drainage time and in the angle of the pipet as it drains (3) temperature fluctuations, which affect the volume of the pipet, the viscosity of the liquid, and the performance of the balance and (4) vibrations and drafts that cause small variations in the balance readings. Undoubtedly, there are many other sources of random uncertainty in this calibration process that we have not listed. Even the simple process of calibrating a pipet is affected by many small and uncontrollable variables. The cumulative influence of these variables is responsible for the observed scatter of results around the mean. 

For continuous contact equipment the material and energy balances are written around a section of column of differential height as shown in Figure 12.8. For the vapor phase the component material balance reads... 

For the vapor phase the component material balance reads... 

Interfacial resistance is present in the thin layer, the coefficient K is almost constant, and one can neglect the effect of drop curvature on the total resistance. For a C02-saturated ethanol droplet of volume V and surface A the ethanol balance reads... 

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