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Friday, November 6, 2009

Oxygen

Oxygen
65% of Body Weight
Oxygen is present in water and other compounds.























Liquid oxygen in an unsilvered dewar flask.
Liquid oxygen is blue.
Warwick Hillier,
Australia National University, Canberra




Oxygen is necessary for respiration. You will find this element in the lungs, since about 20% of the air you breathe is oxygen.

Elements in the Human Body

99% of the mass of the human body is made up of only six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. Every organic molecule contains carbon. Since 65-90% of each body cell consists of water (by weight), it isn't surprising that oxygen and hydrogen are major components of the body.
Here's is a look at the major elements in the body and what these elements do.

Carbon

Carbon is found in every organic molecule in the body.







Photograph of graphite,

one of the forms of elemental carbon.

U.S. Geological Survey




Carbon is ingested in food that is eaten and breathed in as a component of air. It is found in the lungs as a waste product of respiration, carbon dioxide.

Thursday, November 5, 2009

10 Carbon Facts

The Chemical Basis for Life

  1. Carbon is the basis for organic chemistry, as it occurs in all living organisms.
  2. Carbon is a nonmetal that can bond with itself and many other chemical elements, forming nearly ten million compounds.
    Elemental carbon can take the form of one of the hardest substances (diamond) or one of the softest (graphite).
  3. Carbon is made in the interiors of stars, though it was not produced in the Big Bang.
  4. Carbon compounds have limitless uses. In its elemental form, diamond is a gemstone and used for drilling/cutting; graphite is used in pencils, as a lubricant, and to protect against rust; while charcoal is used to remove toxins, tastes, and odors. The isotope Carbon-14 is used in radiocarbon dating.
  5. Carbon has the highest melting/sublimation point of the elements. The melting point of diamond is ~3550°C, with the sublimation point of carbon around 3800°C.
  6. Pure carbon exists free in nature and has been known since prehistoric time.
    The origin of the name 'carbon' comes from the Latin word carbo, for charcoal. The German and French words for charoal are similar.
  7. Pure carbon is considered non-toxic, although inhalation of fine particles, such as soot, can damage lung tissue.
  8. Carbon is the fourth most abundant element in the universe (hydrogen, helium, and oxygen are found in higher amounts, by mass).

Wednesday, November 4, 2009

Carbohydrates

Chemistry of Carbohydrates

Carbohydrates or saccharides are the most abundant class of biomolecules. Carbohydrates are used to store energy, though they serve other important functions as well. This is an overview of carbohydrate chemistry, including a look at the types of carbohydrates, their functions, and carbohydrate classification.

What Is a Carbohydrate?

Carbohydrates are a common class of simple organic compouds. A carbohydrate is an aldehyde or a ketone that has additional hydroxyl groups. The simplest carbohydrates are called monosaccharides, which has the basic structure (C·H2O)n, where n is three or greater. Monosaccharides link together to form oligosaccharides and polysaccharides. Two monosaccharides link together to form a disaccharide.

Functions of CarbohydratesCarbohydrates serve several biochemical functions:

Monosaccharides are a fuel for celular metabolism.
Monosaccharides are used in several biosynthesis reactions.
Monosaccharides may be converted into space-saving polysaccharides, such as glyocogen and starch. These molecules provide stored energy for plant and animal cells.
Carbohydrates are used to form structural elements, such as chitin in animals and cellulose in plants.
Carbohydrates and modified carbohydrates are important for an organism's fertilization, development, blood clotting and immune system function.

Examples of Carbohydrates

Monosaccharides: glucose, fructose, galactose
Disaccharides: sucrose, lactose
Polysaccharides: chitin, cellulose

Carbohydrate Classification

Three characteristics are used to classify monosaccharides:

  • number of carbon atoms in the molecule
  • location of the carbonyl group
  • the chirality of the carbohydrate

aldose - monosaccharide in which the carbonyl group is an aldehyde
ketone - monosaccharide in which the carbonyl group is a ketone
triose - monosaccharide with 3 carbon atoms
tetrose - monosaccharide with 4 carbon atoms
pentose - monosaccharide with 5 carbon atoms
hexose - monosaccharide with 6 carbon atoms
aldohexose - 6-carbon aldehyde (e.g., glucose)
aldopentose - 5-carbon aldehyde (e.g., ribose)
ketohexose - 6-carbon hexose (e.g., fructose)

A monosaccharide is D or L depending on the orientation of the asymmetric carbon located furthest from the carbonyl group. In a D sugar, the hydroxyl group is on the right the molecule when written as a Fischer projection. If the hydroxyl group is on the left of the molecule, then it is an L sugar.

Tuesday, November 3, 2009

Balancing Chemical Equations

Introductory Stoichiometry

A chemical equation describes what happens in a chemical reaction. The equation identifies the reactants (starting materials) and products (resulting substance), the formulas of the participants, the phases of the participants (solid, liquid, gas), and the amount of each substance. Balancing a chemical equation refers to establishing the mathematical relationship between the quantity of reactants and products. The quantities are expressed as grams or moles.
It takes practice to be able to write balanced equations. There are essentially three steps to the process:

  1. Write the unbalanced equation.
Chemical formulas of reactants are listed on the lefthand side of the equation.
Products are listed on the righthand side of the equation.
Reactants and products are separated by putting an arrow between them to show the direction of the reaction. Reactions at equilibrium will have arrows facing both directions.

  • Balance the equation.
Apply the Law of Conservation of Mass to get the same number of atoms of every element on each side of the equation. Tip: Start by balancing an element that appears in only one reactant and product.
Once one element is balanced, proceed to balance another, and another, until all elements are balanced.
Balance chemical formulas by placing coefficients in front of them. Do not add subscripts, because this will change the formulas.

  • Indicate the states of matter of the reactants and products.
Use (g) for gaseous substances.
Use (s) for solids.
Use (l) for liquids.
Use (aq) for species in solution in water.
Write the state of matter immediately following the formula of the substance it describes

Worked Example Problem

Tin oxide is heated with hydrogen gas to form tin metal and water vapor. Write the balanced equation that describes this reaction.


  1. Write the unbalanced equation.
    SnO2 + H2 → Sn + H2O
Refer to Table of Common Polyatomic Ions and Formulas of Ionic Compounds if you have trouble writing the chemical formulas of the products and reactants.


Balance the equation.

Look at the equation and see which elements are not balanced. In this case, there are two oxygen atoms on the lefthand side of the equation and only one on the righthand side. Correct this by putting a coefficient of 2 in front of water:
SnO2 + H2 → Sn + 2 H2O

This puts the hydrogen atoms out of balance. Now there are two hydrogen atoms on the left and four hydrogen atoms on the right. To get four hydrogen atoms on the right, add a coefficient of 2 for the hydrogen gas. Remember, coefficients are multipliers, so if we write 2 H2O it denotes 2x2=4 hydrogen atoms and 2x1=2 oxygen atoms.
SnO2 + 2 H2 → Sn + 2 H2O

The equation is now balanced. Be sure to double-check your math! Each side of the equation has 1 atom of Sn, 2 atoms of O, and 4 atoms of H.

Indicate the physical states of the reactants and products.


To do this, you need to be familiar with the properties of various compounds or you need to be told what the phases are for the chemicals in the reaction. Oxides are solids, hydrogen forms a diatomic gas, tin is a solid, and the term 'water vapor' indicates that water is in the gas phase:
SnO2(s) + 2 H2(g) → Sn(s) + 2 H2O(g)
This is the balanced equation for the reaction. Would you like to see another example of balancing equations?

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