Chemistry

People’s perception of chemistry is influenced by the media.  Movies have often pictured chemists as mad scientists (Dr. Jekyll  and Mr. Hyde, 1931) or as crazy professors (Absent-Minded Professor, 1961, Flubber 1997). Unfortunately, very few people can accurately explain what chemistry is, or what chemists do.  It is no wonder, therefore, that people’s misconceptions about chemical principles abound.  The following are a few common misconceptions.  For each, we have introduced contradictory data from which one may reason to disprove the misconception.

misconception:  Fluid pressure acts only downward.

contradictory data: You feel pressure in both ears when swimming deep in the water, regardless of the way your head is positioned.

correct explanation:  This misconception probably comes from diagrams with arrows showing the downward pressure of the atmosphere or ocean upon objects below. According to Pascal’s principle, all points at the same depth in a fluid experience the same pressure.  If, for example, you release a Styrofoam cup from a bathyscaphe, deep in the ocean, it will not flatten like a pancake, but rather shrink equally in all dimensions so that it is a tiny replica of the original.   Pressure at depth video

misconception:   Ice is always at zero degrees Celsius (32 degree Fahrenheit)

contradictory data: The coldest temperature recorded on Earth is -129 degrees Fahrenheit at Vostok, Antarctica.  How can ice in Vostok remain a warm 32 degrees Fahrenheit (161 degrees warmer) without an external heat source?

correct explanation: Although the temperature of ice can vary widely, the temperature of ice-water  (where solid ice is in equilibrium with liquid water) is stable at zero Celsius.  The temperature of ice-water is widely known, and scientists calibrate temperature probes to zero Celsius by placing them in ice water. This familiarity with ice-water probably leads to the misconception about ice. Solid ice, however, can be colder than zero Celsius if the environment is colder.

misconception: Heat rises

contradictory data: Heat is defined as a form of energy arising from the random motion of the molecules of bodies.  It is not matter, and therefore cannot rise or fall.

correct explanation: Heat can be transferred by conduction, convection or radiation.  Warmer fluids rises above cooler fluids, carrying heat energy with them.  The molecules in warmer fluids are more energetic and widely spaced than those in cool fluids.  As a result, cooler fluids are denser and sink below warmer fluids (warmer fluids rise). 

misconception: Organic farmers use organic chemicals

contradictory data: Organic growers market their produce as “all natural”, but organic chemicals, such as synthetic fertilizers, pesticides and herbicides are man-made.

correct explanation: The adjective “organic” indicates that something was derived from living matter.   Organic farmers use fertilizers derived from living matter (e.g. manure, fish meal, etc.),  and manage pests using biological controls.  The term “organic chemistry” refers to carbon-based chemistry.  This term was derived from the fact that nearly all synthetic carbon-based chemicals are derived from petroleum, a product of decayed, compressed vegetation. Organic farmers, however, do not use synthetic organic chemicals.

Activity 7.5.1 – Clarifying misconceptions in chemistry

Note to teacher:  The following is a list of common misconceptions in chemistry. Give one to each student and instruct them to research  the misconception, explain why it is wrong by reasoning from observed facts and experiences, and provide a correct explanation.  Explanations are found in the answer section in this chapter.

• 1. (example) Objects float because they are lighter than water. Objects float if they are buoyed up by a force greater than their own weight (Archimedes principle).  Some barges are made of concrete and float well because they displace a greater weight of water than their own weight.  Fluids of lower density than water (not lower weight), float on top of water.

  2. Wood floats and rocks sinks.

  3. Liquids in straws and pipettes rise due to suction.

  4. The maximum temperature that water can be is 100ºC. 

  5. The bubbles in boiling water are made of air or oxygen.

  6. Electrons flow at the speed of light in copper wires. 

  7. Cations are positive because they have gained protons

  8. Iron and steel are the only strongly ferromagnetic materials.

  9. The faster a fluid moves, the higher its pressure.

  10. All radioactivity is man-made.

  11. Thermal expansion is due to the expansion of particles of matter. 

  12. Electrons orbit the nucleus like planets around sun

  13. The metric system is more accurate than the other measurement systems. 

  14. Heat and temperature are the same.

  15. There are 92 naturally occurring elements on Earth. 

  16. Solids are completely solid and contain no space.

17.  Air has no mass.

18.  Rusting iron does not change weight.

19.  Drops on the outside of a cold container are due to leakage.

20.  Chemical reactions continue until all the reactants are exhausted. 

21.  Endothermic reactions are never spontaneous

22.  Combustion reactions are endothermic because energy must be added before they will occur. 

23.  The space between electrons and the nucleus is composed of air. 

24.  Oxidation is the addition of oxygen in a reaction. 

25.  Reduction is the removal of oxygen in a reaction.

26.  Electrons enter an electrolytic cell at the cathode, travel through the solution, and exit at the anode.

27.  Energy is released when bonds are broken.