Misconception

The course instructors or professors have not tried to intentionally deceive their students. Most individuals cannot grasp the full depth and detail of any chemical concept the first time that it is presented to them. It has been found that most people learn complex subjects best when first given a basic description of the concepts and then left to develop a more detailed understanding over time. Despite the best elforts of educators, a few misconceptions are at times possibly introduced in the attempt to simplify complex material for freshmen students. The part of this process that perpetuates any confusion is the fact that texts and instructors alike often do not acknowledge the simplifications being presented. 

Example A common misconception is that the conjugate base of a weak acid is strong This is sometimes but not always true It is true for example for ammo nia which is a very weak acid (pK 36) Its conjugate base amide ion (H2N ) is a much stronger base than HO It is not true however for acetic acid both acetic acid and its conjugate base acetate ion are weak The conjugate base of a weak acid will be strong only when the acid is a weaker acid than water... 

A common misconception is that a stereospecific reaction is simply one that is 100% stereoselective The two terms are not synonymous however A stereospecific reac tion IS one which when carried out with stereoisomeric starting materials gives a prod uct from one reactant that is a stereoisomer of the product from the other A stereo selective reaction is one m which a single starting material gives a predominance of a... 

Reported cases of vitamin toxicity owing to overdose are usually associated with increased over-the-counter availabiHty of supplemental vitamins and indiscriminate supplementation. The misconception that if a Httle is good a lot is better has compounded toxicological problems with the vitamins. Eat-soluble vitamins tend to accumulate in the body with relatively inactive mechanism for excretion and cause greater toxicological difficulties than do water-soluble vitamins. 

Many misconceptions exist about cascade control loops and their purpose. For example, many engineers specify a level-flow cascade for every level control situation. However, if the level controller is tightly tuned, the out-flow bounces around as does the level, regardless of whether the level controller output goes direcdy to a valve or to the setpoint of a flow controller. The secondary controller does not, in itself, smooth the outflow. In fact, the flow controller may actually cause control difficulties because it adds another time constant to the primary control loop, makes the proper functioning of the primary control loop dependent on two process variables rather than one, and requites two properly tuned controllers rather than one to function properly. However, as pointed out previously, the flow controller compensates for the effect of the upstream and downstream pressure variations and, in that respect, improves the performance of the primary control loop. Therefore, such a level-flow cascade may often be justified, but not for the smoothing of out-flow. 

There are numerous misconceptions about the sources of various chemical elements in waste, particularly those that are potential acid formers when the waste is incinerated or mechanically converted and used as a refuse-derived fuel. For example, it is often mistakenly stated that the source of chlorine in waste, hence a potential source of HCl emissions, is poly(vinyl chloride). The relative contents of selected, potentially acid-forming elements in the organic portion of a sample of waste collected from various households in one U.S. East Coast city is given in Table 2 (17). In this city, a chief source of chlorine in the waste is NaCl, probably from food waste. 

Fermentation. The term fermentation arose from the misconception that black tea production is a microbial process (73). The conversion of green leaf to black tea was recognized as an oxidative process initiated by tea—enzyme catalysis circa 1901 (74). The process, which starts at the onset of maceration, is allowed to continue under ambient conditions. Leaf temperature is maintained at less than 25—30°C as lower (15—25°C) temperatures improve flavor (75). Temperature control and air diffusion are faciUtated by distributing macerated leaf in layers 5—8 cm deep on the factory floor, but more often on racked trays in a fermentation room maintained at a high rh and at the lowest feasible temperature. Depending on the nature of the leaf, the maceration techniques, the ambient temperature, and the style of tea desired, the fermentation time can vary from 45 min to 3 h. More highly controlled systems depend on the timed conveyance of macerated leaf on mesh belts for forced-air circulation. If the system is enclosed, humidity and temperature control are improved (76). 

There are many common misconceptions about vinyl. Eor example, the idea that vinyl is not recycled is untme. Industrial scrap vinyl has been recycled for years, but in more recent years, post-consumer vinyl recycling is growing, too, with about 3.25 x 10 tons (6.5 x 10 lb) of post-consumer vinyl (primarily botdes) being recycled in the 1990s. When the Council for SoHd Waste Solutions (now the American Plastics Council) conducted a nationwide survey in 1991, it found that there were an estimated 1100 municipal recycling programs in place or plaimed in the United States that include vinyl. 

The misconception that vinyl gives off dioxin when it is incinerated is misleading. A study conducted by ASME in 1995 (162) found that the presence, or absence, of chlorine-containing wastes in incinerators had no effect on the levels of dioxin produced. Rather, it was found that incinerator operating conditions (primarily temperature) were the key to controlling dioxin formation. More recentiy, German officials examined the issue of incinerating vinyl waste and decided there was no cause for concern (180). 

The true influence of flaws and defects on component failure is commonly misunderstood. This misunderstanding often arises from one of two misconceptions. The first misconception can be clarified by simple definitions of a flaw and a defect. 

The second misconception involves the perception of what constitutes a defect. A defect is not simply a visually observable discontinuity such as a hole, lap, or seam in a component. Defects, from a failure-analysis standpoint, may also be such things as a high residual stress that may lead to cracking or unfavorable microstructures that can lead to either... 

All areas of the cooling water system where a specific form of damage is likely to be found are described. The corrosion or failure causes and mechanisms are also described. Especially important factors influencing the corrosion process are listed. Detailed descriptions of each failure mode are given, along with many common, and some not-so-common, case histories. Descriptions of closely related and similarly appearing damage mechanisms allow discrimination between failure modes and avoidance of common mistakes and misconceptions. 

Table 1 shows prevalent examples of misconceptions about QRA. Many are actually generalizations that are too broadly applied. Two of the most common misconceptions concern (1) the lack of adequate equipment failure data and (2) the cost of performing QRA. 

Chapter 1 defines QRA, discusses its essential elements, and dispels some misconceptions. Chapter 2 outlines considerations for deciding when to apply QRA. It presents some reasons for performing QRA and describes the types of information available from such studies. This chapter also describes practical situations in which QRA may be used successfully, as well as conditions that make QRA a less desirable choice. 

It is a popular misconception that plastics are cheap materials. They are not. On a weight basis most plastics are more expensive than steel and only slightly less expensive than aluminium. Prices for plastics can range from about 600 per tonne for polypropylene to about 25,000 per tonne for carbon fibre reinforced PEEK. Table 1.5 compares the costs of a range of plastics. 

The description of the physical characteristics of ventilation noise is based on more reliable knowledge than the description of the human effect. Misconceptions about the levels and frequency characteristics of ventilation noise are still common. This in turn has sometimes led to wrong suggestions about the measures that should be taken in order to eliminate the effects of a ventilation noise exposure. 

However, Scheele believed he had prepared a compound (dephlogisticated marine acid air) and the misconception was compounded by C.-L. Berthollet who showed in 1785 that the action of chlorine on water releases oxygen tCl2(g) -F... 

Myths and misconceptions about the characteristics of supercritical fluids have slowed their application to chromatographic separations. While these fluids do have interesting properties, they are not super fluids, and they are not suitable for all types of separations. An understanding of the fundamental behavior of supercritical fluids is key to identifying appropriate applications [10]. 

Karassik, 1., Fact or Fiction Some Misconceptions About Desirable Construction Features of Centrifugal Pumps, Chemical Processing Mid-March 1989. 

One of the most effective methods of preventing corrosion is the selection of the proper metal or alloy for a particular corrosive service. Once the conditions of service and environment have been determined that the equipment must withstand, there are several materials available commercially that can be selected to perform an effective service in a compatible environment. Some of the major problems arise from popular misconceptions for example, the use of stainless steel. Stainless steel is not stainless and is not the most corrosion-resistant material. Compatibility of material with service environment is therefore essential. For example, in a hydrogen sulfide environment, high-strength alloys (i.e., yield strength above 90,000 psi or Rc 20 to 22) should be avoided. In material selection some factors that are important to consider are material s physical and chemical properties, economics and availability. 

Arctic Drilling. Corrosion problems encountered in arctic area drilling are no different from problems faced in other areas of the world. It is a general misconception that during arctic drilling corrosion-related problems are either not very severe or totally absent due to low temperatures. Cool temperatures may slow down the corrosion process. However, they also increase the solubility of oxygen, carbon dioxide and hydrogen sulfide. Therefore, the net result can be an increase in the rate of corrosion. While cold temperatures may cause problems, the temperature fluctuation common in arctic environments can be a more severe source of corrosion-related problems [215]. 

Fitzpatrick, M., Common Misconceptions About the RCRA Subtitle C Exemption from Crude Oil and Natural Gas Exploration, Development and Production, Proceedings from the First International Symposium on Oil and Gas Exploration Waste Management Practices, pp. 169-179, 1990. 

A contract is made when the essential elements have been fulfilled and the offer and acceptance communicated, and, apart from contracts involving land, can be verbal. A common misconception is that a party signs a contract. In reality, a party signs a document, which contains the terms of the contract being entered into. Almost all contract documents omit many matters, which are important, and the reason for this is that the law says that certain matters are implied to be contained within a contract. An example is that if X buys an item of plant from y it is implied that X will receive it within a reasonable time, and that it will be of merchantable quality when he receives it. 

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