Catalyst Lab Academic Chem
By Michelle Penoyer
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Last updated over 1 year ago
10 Questions
Introduction:
We tend to think of ourselves as good observers. Yet there is much more to observation than meets the eye. It takes concentration, alertness to detail, ingenuity and patience. It also takes practice. Besides using your eyesight, the sense of smell, touch, taste and sound can also be used to make observations.
A physical property can be measured and observed without changing the composition or identity of a substance – for example, density, color, taste, hardness, and melting point.
Physical changes are changes affecting the form of a chemical substance, but do not change the chemical composition of that substance. Physical changes are used to separate mixtures into their component compounds. Examples of physical changes include changes of state such as melting, freezing, boiling, condensing, subliming. Cutting a sheet of paper and breaking a crystal are other examples of physical changes. Dissolving a substance in water or another solvent without any reaction is also an example of a physical change.
On the other hand, "hydrogen gas burns in oxygen gas to form water" describes a chemical property of hydrogen. Chemical properties can be measured and observed when the composition changes. Chemical changes occur when a substance combines with another to form a new substance. These processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. Some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. Some terms that generally indicate a chemical reaction include decompose, explode, rust, oxidize, corrode, tarnish, ferment, burn, or rot. Understanding chemical changes is a major part of the science of chemistry. There are five observations that indicate that a chemical change has occurred: Odor change, temperature change, color change, a solid produced called a precipitate, or a gas produced.
Catalyst
V2O5
2 SO2(g) + O2(g) -----> 2 SO3(g)
Reactants Products
SO2 is a severe irritant to the respiratory tract, eyes, mucous membranes, and skin. Exposure to high doses can cause pulmonary edema, bronchial inflammation, laryngeal spasm, and edema with possible airway obstruction. SO2 is most noteworthy as an environmental pollutant. It is formed when materials containing sulfur are burned and is thus an important air pollutant, especially in the vicinity of smelters and plants burning soft coal or high-sulfur oil. Others are automobile exhaust, wood-burning stoves, pulp mills, and smelters. Note that, in addition to SO2 itself, many related compounds and decay products of SO2: such as sulfurous and sulfuric acids, sulfates, sulfites, and bisulfites--are present in the ambient air.
SO2 is a pollutant that reacts with oxygen gas to form SO3. Then SO3 reacts with water to form H2SO4 in the reaction shown:
SO3 + H2O ---> H2SO4
The reaction above is an unfortunately common reaction that occurs in the atmosphere in some places where oxides of sulfur are present as pollutants. The acid formed in the reaction falls to the ground as acid rain. Acid rain has severe consequences on both man-made objects and nature. Acid rain degrades marble statues and can kill trees in forested areas with incidents of acid rain.
MnO2
2 NaClO3 --------→ 2 NaCl + 3 O2
The reaction shown above is used on airplanes to generate oxygen in case of an emergency. Aviation regulations require that an emergency oxygen supply is available to passengers in the event that there is a loss of cabin pressurization at an altitude where the partial pressure of oxygen would be insufficient to sustain consciousness. The weight, complexity, and maintenance issues associated with an oxygen tank system mean that the majority of transport aircraft use chemical oxygen generators to provide emergency oxygen for occupants of the passenger cabin.
Oxygen generators are usually installed above each seat row. If the cabin altitude reaches a predetermined height (14,000' is standard), or if the system is activated by the flight crew, overhead panels open and oxygen masks drop out. To put the mask on, it is necessary for the intending user to pull it down and this action releases the firing pin and activates the generator.
The oxidizer core of an oxygen generator usually consists mainly of NaClO3 mixed with <5% Barium Peroxide (BaO2) and <1% Potassium Perchlorate (KClO4). This core is activated by the application of heat, which is normally generated by a mixture of lead styphnate and tetracene which itself is activated by a small explosive charge in a percussion cap. This explosive charge is set off by the release of a spring-loaded initiation mechanism which is restrained until released by a pull on the lanyard which is visible when oxygen masks are released from overhead panels. Once activated, the chemical reaction and production of oxygen will continue until the generator has been exhausted, typically in the range of 12 to 20 minutes depending upon the type and size of the generator installed. The reaction of the chemicals produces a significant amount of heat and the generator canister in the overhead compartment can reach temperatures above 250°C. The effect of this is that an often-unanticipated burning smell may become apparent in the passenger cabin and cause alarm.
The amount of oxygen that must be able to be produced by an installed cabin oxygen generator, as a function of time, is not constant. The requirement depends on the maximum operating altitude of the aircraft and the emergency descent profile which it is expected to follow after a loss of cabin pressure before it reaches an altitude, generally 10,000 feet, where supplementary oxygen is no longer necessary. Also, since the amount of oxygen required at higher altitudes will be greater than that needed at lower altitudes, the chemical core of the generator has a larger diameter at the initiation end than at the outlet end so that relatively more oxygen is produced at the beginning of the reaction.
Each oxygen generator is attached to a number of emergency oxygen masks by plastic tubes. There is a regulatory requirement to provide at least 10% more masks than there are seats so some seat rows will have an extra mask available. This allows an additional mask in the event that someone has an infant in their lap or that someone in the aisle requires one. In the event of an onboard fire, passenger oxygen masks should not be deployed as the production of oxygen may worsen the situation.