Avoid this mistake

Be sure, especially in stoichiometry problems involving gases, that you are calculating the values such as volume and pressure of the correct gas. You can avoid this mistake by clearly labeling your quantities that means, mol of 02 instead of just mol. 

A common mistake is to write 2x1 You can avoid this mistake by using brackets. 

A student wishes to measure the absorptivity (a) of compound X in water at a concentration (c) of 2 milligrams per liter in a one centimeter pathlength b) glass cuvet at a wavelength of 150 nanometers. The measured absorbance A is found to be 4.0. What value would the student obtain for the absorptivity al The true value is 0. Why might the student have obtained the wrong value How could she have designed a set of experiments to avoid this mistake ... 

Problem 23.24 The sulfonamides of big primary amines are only partially soluble in aqueous KOH. (a) In the Hinsberg test, what incorrect conclusion might you draw about such an amine (b) How might you modify the procedure to avoid this mistake ... 

The primary fear of many of the scientists and firms involved in biotechnology revolution is obviously the Type III mistake—that there will be an unreasonable suppression of the development. But avoiding this mistake is closely tied to our ability to avoid a Type II mistake. The more confident society is that releasing the fruits of biotechnology experiments will not create unexpected problems, the less likely it is to impose oppressive restrictions on this development. The key question is whether we can be confident of avoiding Type II errors without implementing such controls. 

Intra-operative and post-operative imaging of fractures stabilised with intra-medullary devices requires views in at least two planes, not only to visualise the adequacy of the bone alignment but also to check the position of the implants. Elastic intramedullary nails may appear to be within the bone in one plane but may be seen to lie outside the bone when viewed from a different angle (Fig. 9.4a,b). The nail will have either failed to traverse the fracture site (more common in long spiral fractures) or the sharp tip of the nail will have penetrated the cortex. This is particularly likely around the calcar (femoral neck) and lesser trochanter because the procurva-tum of the femur tends to guide the medial nail in a dorsal direction. Imaging of the hip joint is difficult but crucial to avoid this mistake. 

Reversing the direction of one or more arrows during a chemical step is the most common mistake made by students when writing organic reaction mechanisms. Backward arrow pushing usually derives from a student thinking about the movement of atoms, not the movement of electrons. Hence, to avoid this mistake it is important to remember that arrows depict how electrons move, not where atoms move, within or between chemical structures. Further, one can avoid this mistake by remembering that every arrow must start at an electron source (a bond or lone pair) and terminate at an electron sink (an atom that can accept a new bond or lone pair). 

Likely the most common mistake is pushing the arrow backwards. In other words, the arrow is started at a sink and ended at a source. Three examples are given below. The easiest way to avoid this mistake is to remember that the arrow must start from an electron rich region of a molecule. Most important, the arrow always starts with two electrons—namely, lone pairs, o bonds, or tt bonds. Do not use the positive regions of a molecule to start an arrow. The vast majority of the time the arrow will terminate at a center with some positive charge or a center that can accept a lone pair. 

This is a check on the reasonableness of the method chosen. For example, it would not be reasonable to select a method to investigate vibrational motions that are very anharmonic with a calculation that uses a harmonic oscillator approximation. To avoid such mistakes, it is important the researcher understand the method s underlying theory. 

This book gives a broad introduction to these properties and limitations. It cannot make you a materials expert, but it can teach you how to make a sensible choice of material, how to avoid the mistakes that have led to embarrassment or tragedy in the past, and where to turn for further, more detailed, help. 

Highly concentrated ether carboxylic acids with a low degree of ethoxylation even at room temperature can give an esterification reaction with the non-converted nonionic, especially with the fatty alcohol, to several percentage points. The result may be that a too low value is found for the ether carboxylate content. This mistake in analysis can be avoided by saponification of the formed ester [238]. Two hundred to 300 mg matter and ca 100 mg NaOH were weighed in a 50-ml Erlenmeyer glass, heated with 20 ml ethanol under reflux, and after cooling supplied with water to 100 ml. Afterward a two-phase titration was carried out. 

This combined manual is designed to help students avoid common mistakes and understand the material better. The solutions manual includes detailed solutions to all odd-numbered exercises in the text, except for the Chemistry Connections exercises. 

Terrence Collins is the Thomas Lord Professor of Chemistry at Carnegie Mellon University who contends that the dangers of chlorine chemistry are not adequately addressed by either academe or industry, and alternatives to chlorine and chlorine processors must be pursued. He notes, Many serious pollution episodes are attributable to chlorine products and processes. This information also belongs in chemistry courses to help avoid related mistakes. Examples include dioxin-contaminated 2,4,5-T, extensively used as a peacetime herbicide and as a component of the Vietnam War s agent orange chlorofluorocarbons (CFCs) polychlorinated biphenyls (PCBs the pesticides aldrin, chlordane, dieldrin, DDT, endrin, heptachlor, hexachlorobenzene, lindane, mirex, and toxaphene pentachlorophe-... 

The College Board uses some exams to help train high school teachers so that they can help the next generation of chemistry students to avoid common mistakes. If you check this box, you simply give permission to use your exam in this way. Even if you give permission, no one will ever know it is your exam. 

Shutdown and startup activities, as well as changes made to prepare for maintenance, can sometimes require some abnormal activity. It is essential that sufficiently trained individuals develop and review these little changes from normal practice to avoid the mistakes recorded in this chapter. 

In addition, 3D imaging also allows the trained eye to identify other important parameters such as e.g. the distance between the probes and whether the probes are colocalized (2D systems simply cannot reveal this). Furthermore, the documented improved accuracy and precision of 3D images help avoid potential mistakes such as image distortion and magnification common with 2D imaging technology. 

Before we illustrate this procedure, let s consider a few common mistakes. Avoiding these mistakes will help you to draw correct mechanisms throughout this course. 

The determination of photochemical quantum yields is not a simple task, and, in some cases, approximations are required. Nevertheless, according to the parameters chosen, various well-known photochemical reactions can be used to measure irradiance, which is an essential quantity in the field of photokinetics. Finally, some selected chemical actinometers will be discussed with respect to their pros and cons and their best areas of application. At the end, special applications of actinometry such as measurements of polychromatic light and high-intensity light sources (lasers) will be described. The overall aim of this chapter is to help the reader to choose the best actinometers out of the numerous examples in the literature and avoid technical mistakes. 

Particle diameter is included in the correlation as (dp/D). Chowdhury (1997 Penney et al., 1997) and others have found that Njs is virtually independent of (dp/D) for (dp/D) > 0.01. This is of no practical importance for large vessels where D could be 40" and it would be unlikely to encounter particles larger than 0.4" diameter however, it could give underpowered agitators for scale-up from small vessels where the minimum D could be 2" and the maximum dp could be 0.2", for a maximum (dp/D) = 0.1, which is 10 times (dp/D) = 0.01. Scale-up at equal P/V, which is typical for sohds suspension, could give an Njs about 100/(10) 2 = 60% of the required Njs. Avoid this scale-up mistake by using accurate suspension correlations to determine Njs for plant vessels, when scahng-up from laboratory experiments where (dp/D) >0.01. 

Very strong acids and bases will dissociate almost completely. This means that the HA or BOH concentration (for the acid and base respectively) will be nearly zero. Since division by zero is impossible, for such acids and bases, there is no Ka or Kh. Surprisingly, this fact makes it easier to find the pH of strong acid and strong base solutions. Since the entire concentration of acid or base is assumed to dissociate, the concentration of H or OH" is the same as the original concentration of acid or base. For instance, a 0.01 molar solution of HC1 will have 0.01 mol L 1 of H+ ions. Since 0.01 = 10 2, and -log(10"2) = 2, the pH of the solution will be 2. Likewise, in a 0.01 molar solution of NaOH, we will have 0.01 mol L 1 of OH" ions. (Be careful here ) The pOH will equal 2 so the pH will equal 12. You can avoid a mistake here by remembering that an acid has a pH below 7 and a base has a pH above 7. 

When all parental aspirations are centered on a single child, the pressure from that ambition can cause the boy or girl to try to do everything right, to be as successful as parents want, to demonstrate that he or she is after all, and first of all, the exceptional child they wanted. To strive to fulfill this unrealistic ideal, the only child must endure the twin pressures that perfectionism creates to live error-free (to avoid making mistakes at all costs), and to always excel (and not fail at all costs). 

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