Chemistry

Experiment A-7

It is not clear why human minds do so, but eventually we want to understand what we have observed and interpreted about the world around us.  We have historical records of early attempts to understand earthly materials starting over 2500 years ago.

The Greeks were among the first to propose physical explanations for materials.

Thales (of Miletos 624-546 B.C.) developed a Babalonian idea that the world was created from the waters.  He suggested that every substance is but a single reality, water, but appearing in different forms.  Water exhibits all the known states of matter, solid, liquid, and gaseous, and is clearly essential to life as well.

Anaximandros (of Miletos 610 to 545 B.C.) agreed with Thales that the world is made of some basic element.  But Anaximandros thought that element was some undetermined material: apeiron.

Anaximenes (of Miletos about 590 to 526 B.C.) claimed that air (pneuma) is the elemental material.  Variety of substance is due to thickening or thinning.

Heracleitos (flourishing in Ephesos in 484 B.C.) suggested everything consists of fire or some other single material and that is changed by eternal flux (then meaning up and down motion).

Anaxagoras (of Clazomenae perhaps 500 to 428 B.C.) suggested the world is essentially complex and divisible seeds controlled by mind (Nus)  The component seeds of everything are the same nature as the thing itself.

Empedocles (of Agrigentum 492 to about 400 B.C.) combined aspects of the previous ideas.  Empedocles suggested that everythings consists of four elements: Fire, air, water, and earth, and two forces: love (attraction) and strife (repulsion).  (Fire and these other elements were thought to be related to what we observe, but more pure.)

Aristotle (of Stageira 384 to 322 B.C.) compiled a consistent account of all knowledge.  Aristotle included Empedocles four elements of the world (Fire, air, water, and earth), but added a fifth element (æther) to account for the material of heavenly objects.

Unlike his teacher Plato, Aristotle believed that truth is found by observing the universe.  This became one of the tenants of science.  Aristotle was primarily an encyclopedist.  While earlier philosophers had also tried to explain the universe, Aristotle was the first to realize it was first necessary to inventory and describe.  Generalizations are derived from the observation of many examples.  Aristotle invented the rules of logic, a process necessary for science!

Aristotle tutored Alexander (the Great), who widely spread Aristotle's teachings.  Largely as a result, Aristotle's teachings, including the four earthly elements, remained accepted until the 18th Century!

Nearly a century earlier, Leucippos (perhaps born about 450 B.C. in Miletos) proposed an idea of materials that Aristotle found inconsistent with the concept of five elements.  Leucippos suggested that the universe is composed of an infinite variety of small particles.  The idea of Leucippos was developed by Democritos (born about 420 B.C. in Abdera) who studied with the learned men during his extensive travels.  Democritos claiming substances of the world are divided into small particles called atoms.  The atoms are infinite in number, indivisible, indestructible, and absolutely simple.  Observed changes are due to continual aggregation and disaggregation of atoms in an infinity of ways.  The empty space between atoms is void.

The comprehensive atomic explanations of Democritos could explain most known facts.  However Aristotle adopted the parallel but conflicting ideas of Empedocles about elements, which because of Alexander's influence became the accepted explanation of materials for the next 2000 years.  The concept of atoms languished in the backwaters of historical archives until more advanced observations and measurements needed such an idea to provide explanation.

Over the next 2000 years alchemists adopted the Greek explanations summarized by Aristotle and technology from the Babylonians and Egyptians to develop a secret, codified art for causing chemical changes and producing alloys which they sold providing for their living.  They significantly increased the body of known facts about ores and other minerals, discovered alkalis, and developed a penchant for carefully weighing ingredients to assure consistent products.

Robert Boyle (1627 to 1691, engraved at right→) criticized the FOUR ELEMENT THEORY and the THREE PRINCIPLES added by alchemists as not agreeing with the chemical facts.  Boyle requested chemists to review the experiments and devise a new theory.   Boyle proposed a new definition of element: A substance that cannot be decomposed into any simpler substance.  Boyle suggested the value of the ATOMIC THEORY of Democratus.  He began studies of air that inspired others to later find inadequacies in the FOUR ELEMENT THEORY.

Over the next century the collection and handling of gases was developed resulting in the discovery that a variety of airs could be created with very distinct properties.  While a theory involving the proposed substance Phlogiston tried to explain new observations and properties, inconsistencies and incorrect predictions, particularly of mass changes, raised doubts about the theory's validity.

For 101 days beginning October 1768 Antoine Lavoisier (1743 to 1794, in Paris) distilled and condensed water in a sealled container.  Its weight remained unchanged.  Water is inconvertable!

Antoine Lavoisier married Marie-Anne Pierrette in 1771.  She learned English to keep Antoine abreast of chemical progress occuring in England.  She helped with the experiments, recorded observations and results, and drew sketches for his notebook and publications.  They lived in an age when accomplishments were attributed to men.  But perhaps the new chemistry of Lavoisier should be considered the product of their teamwork. (their portrait at right→)

In 1772 he found, contrary to the Phlogiston theory, that burning both phosphorus and sulfur increases their weights, producing acid forming gases.

When the English chemist Joseph Priestly visited Paris in October 1774, he met Lavoisier and shared his discovery of dephlogisticated air. Lavoisier amplified Priestly's experiment to prove that that air absorbed by heating Mercury gently to form the red calx is exactly the same volume as the dephlogisticated air liberated by heating more strongly.

Convinced that evidence was finally at hand showing that air and water are not single elements, Lavoisier believed that Boyle's century old proposed definition of element could explain all the distinctly different airs as well as the weight contradictions in the Phlogiston theory.  Elements are the substances we have not discovered means for separating.  They are all the substances into which we are capable to reduce (in weight) bodies by decomposition.  Lavoisier conducted a great systematic series of experiments, reporting the results periodically in memoirs to the Academie Royale des Sciences.

All the while Laviosier was heavily engaged in official duties as fermier generale (financiers that leased the right for French tax collections on commerce).  He also was active promoting improvements for French political, social, and economic conditions.

Lavoisier published in 1789 the Traite elementaire de Chimie... describing a revolutionary new system of chemistry.  Lavoisier's book describes the new chemistry: besides the new concept of element, it contains

1. a vast amount of experimentally observed facts,
2. Lavoisier's explanations for those facts, and
3. the new rational system of nomenclature Lavoisier believed essential.

Underlying the new chemistry is the assumption that matter is conserved.  Weight becomes the tool for determining if a product is simplier or more complex than an ingredient.

The Four Element Theory was rapidly abandoned by most chemists:  Each distinctive Air becomes a different gas, many of them elements.  Water becomes a compound of the elements Hydrogene and Oxygene.  Earth is a variety of substances, mostly compounds.  Fire becomes two elements: Calorique (heat) and Lumiere (light).

The metal compounds studied by the alchemists become seventeen different elements.  Mercury is merely one of the metallic elements.  Mixtures of metals become alloys.

Combustion is the process of combination with Oxygene.  All acids are compounds containing Oxygene and a distinctive element.  Soufre (Sulfur) is one of six nonmetallic acidifiable elements.  Salts are the combination of acids and either metals or earthly bases.  Lavoisier expected the Alkalies to be found to be compound.

Experiment

Lavoisier suggested a much different explanation, claiming that the elementary composition of the water remained a fixed compound of the elements Oxygen and Hydrogen throughout.  Only their physical state of existence changed by adding or removing calorique (= heat we still measure as calories).  Lavoisier wrote That solidity, liquidity, and aeriform elasticity, are only three different states of existence of the same matter, or three particular modifications which almost all substances are susceptible of assuming successively, and which solely depend upon the degree of temperature to which they are exposed;  or, in other words, upon the quantity of caloric with which they are penetrated.  A footnote adds The degree of pressure which they undergo must be taken into account.

Materials

• tiny amount of ice
• quart, zip-locked bag or equivalent flexible, easily popped bag; do NOT use a rigid container.
• microwave oven or other heating device
• freezer
• safety goggles, gloves, long sleeved jacket and pants
• device for estimating volume (ruler?)

Procedure

1. Put a small amount of ice (less than ½ cm³) in a zip-lock bag (Too much ice will cause the bag to open making your measurement invalid.)
   
   
2. Estimate the volume of ice.
   
   
3. Remove as much air as possible before closing the bag
   
   
4. Allow the ice to melt at room temperature.
   
   
5. Estimate the volume of liquid water produced.
   
   
6. Steam can cause severe, painful burns and under some circumstances, death.  PLAN AHEAD to avoid any accidental steam burn.  Do not directly touch the bag containing steam.  Wear safety goggles, gloves, and cloth arms and legs to keep any accidental steam leak from scalding skin.  (After an experiment with no accident or injury, it sometimes seems like the safety precautions were a wasted time and effort.  But bad accidents are rarely expected!  If safety precautions only save your life once from your own or someone else's bad error, it will make all those seemingly wasted efforts worth it.)  Heat the bag containing the liquid water for the minimum amount of time needed to boil the water.  (If you have trouble getting all the water to boil, try setting it on an overturned styrofoam cup or placing it on a styrofoam or paper plate which will be slow to cool the steam.)
   
   
7. Estimate the volume of steam produced without touching the bag.
   
   
8. Allow the bag to cool and the steam to condense to liquid.
   
   
9. Estimate the volume of liquid water.
   
   
10. Place the cool bag in the freezer until all the liquid has frozen.
    
    
11. Estimate the volume of ice produced.
    
    
12. Calculate the ratio between the volume of the liquid water and the volume of ice.
    
    
13. Calculate the ratio between the volume of steam and the volume of the liquid water.
    
    
14. Consider the possible causes and sizes of error in your estimates and calculations.
    
    
15. Calculate how much water expands (or contracts) in each linear direction if it were composed of Aristotle's elements.
    
    
16. What difference would it make if water is as Lavoisier suggested rather than as Aristotle proposed?  (Scientists like to find a key experiment where rival theories predict different observable or measurable results.)

If you need course credit, use your observations recorded in your journal to construct a formal report.