The Chemistry Of Carbon Compounds

Carbon is a chemical element( A chemical element or element is a species of atoms having the same number of protons in their atomic nuclei (i.e. the same atomic number)),with symbol C and atomic number 6.

Atomic Number is the number of protons found in the nucleus of an atom of that element. Remember proton is a subatomic particle, symbol p or p+, with a positive electric charge of +1e elementary charge

Carbon is the fourth most abundant element in the universe, and is absolutely essential to life on earth. Every organism on Earth needs carbon either for structure, energy, or, as in the case of humans, for both. Discounting water, YOU are about half carbon. Additionally, carbon is found in forms as diverse as the gas carbon dioxide (CO 2 ), and in solids like limestone (CaCO 3 ), wood, plastic, diamonds, and graphite.

Carbon is the lightest element on the periodic table that has four valence electrons. If each valence electron is used to form a bond with another atom, carbon reaches 8 electrons in its valence shell and is stable. Elements with either less or more than 4 valence electrons can only form a maximum of 3 covalent bonds, this is why 4 is a magic number and why carbon is special.

Compounds of Carbon

Compounds of carbon are defined as chemical substances containing carbon. More compounds of carbon exist than any other chemical element except for hydrogen. Organic carbon compounds are far more numerous than inorganic carbon compounds. In general bonds of carbon with other elements are covalent bonds.

KEY POINTS:*Organic chemistry is often defined as the chemistry of carbon*

The chemistry of carbon is dominated by three factors.

1. Carbon forms unusually strong C-C single bonds, C=C double bonds, and carbon-carbon triple bonds.

2. The electronegativity of carbon (EN = 2.55) is too small to allow carbon to form C4-ions with most metals and large for carbon to form C4+ ions when it reacts with nonmetals. Carbon therefore forms covalent bonds with many other elements.

3. Carbon forms strong double and triple bonds with a number of other nonmetals, including N, O, P, and S.

 

four carbon bonds

Allotropes of Carbon

Carbon occurs as a variety of allotropes. There are two crystalline forms -- diamond and graphite--and a number of amorphous (noncrystalline) forms, such as charcoal, coke, and carbon black.

The properties of diamond are a logical consequence of its structure. Carbon, with four valence electrons, forms covalent bonds to four neighboring carbon atoms arranged toward the corners of a tetrahedron,  Each of these sp3-hybridized atoms is then bound to four other carbon atoms, which form bonds to four other carbon atoms, and so on. As a result, a perfect diamond can be thought of as a single giant molecule. The strength of the individual C-C bonds and their arrangement in space give rise to the unusual properties of diamond.

Graphite consists of extended planes of sp2-hybridized carbon atoms in which each carbon is tightly bound to three other carbon atoms. (The strong bonds between carbon atoms within each plane explain the exceptionally high melting point and boiling point of graphite).

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STATES OF MATTER

What is matter:  matter is made of atoms. Atoms are the smallest particle of matter. They are so small that you cannot see them with your eyes or even with a standard microscope. A standard sheet of paper is about a million atoms thick. Matter is the air you are breathing. Matter is the computer you are reading from now. Matter is the stuff you touch and see. And it is more. Matter is defined as anything that has mass and takes up space.

STATES OF MATTER AND THEIR PROPERTIES. 

Some states(phases) of matter are;

1. SOLIDS:  Solids hold their shape at room temperature. The pencil that you left in the desk at school will still be the same shape when you return tomorrow.

Pencil

Even in solids there is a small space between the atoms. Depending on how tight the atoms are packed determines the density matter. This means that a one inch block of wood is not as dense as a one inch block of gold. There is more space between the atoms of the wood than the atoms of the gold.

2. LIQUIDS: Liquids do not hold their shape at room temperature. There is space between the atoms of a liquid and they move slightly all of the time. This allows you to stick your finger into water and pull it back out, letting the water fill back in where your finger once was. When a solid is heated above its melting point, it becomes liquid, given that the pressure is higher than the triple point of the substance.

3.GASES: A gas is a compressible fluid. Not only will a gas conform to the shape of its container but it will also expand to fill the container.In a gas, the molecules have enough kinetic energy so that the effect of intermolecular forces is small (or zero for an ideal gas), and the typical distance between neighboring molecules is much greater than the molecular size. A gas has no definite shape or volume, but occupies the entire container in which it is confined. A liquid may be converted to a gas by heating at constant pressure to the boiling point, or else by reducing the pressure at constant temperature.

4. PLASMA: Plasma does not have definite shape or volume. Unlike gases, plasmas are electrically conductive, produce magnetic fields and electric currents, and respond strongly to electromagnetic forces. Positively charged nuclei swim in a “sea” of freely-moving disassociated electrons, similar to the way such charges exist in conductive metal. In fact it is this electron “sea” that allows matter in the plasma state to conduct electricity. Lightning, electric sparks, fluorescent lights, neon lights, plasma televisions, some types of flame and the stars are all examples of illuminated matter in the plasma state.

5. Bose-Einstein condensates: In 1995, technology enabled scientists to create a new state of matter, theBose-Einstein condensate (BEC). Using a combination of lasers and magnets, Eric Cornell and Carl Weiman cooled a sample of rubidium to within a few degrees of absolute zero. At this extremely low temperature, molecular motion comes very close to stopping altogether. Since there is almost no kinetic energy being transferred from one atom to another, the atoms begin to clump together. There are no longer thousands of separate atoms, just one “super atom.” A BEC is used to study quantum mechanics on a macroscopic level. Light appears to slow down as it passes through a BEC, allowing study of the particle/wave paradox. A BEC also has many of the properties of a superfluid — flowing without friction. BECs are also used to simulate conditions that might apply in black holes.

OXYGEN AS A LIQUID

WHAT IS OXYGEN? 

Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table and is a highly reactive non metal and oxidizing agent that readily forms compounds (notably oxides) with most elements. By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium.

Key point: The chalcogens  are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. It consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the radioactive element polonium (Po).

Oxygen was discovered independently by Carl Wilhelm Scheele, in Uppsala, in 1773 or earlier, and Joseph Priestley in Wiltshire, in 1774, but Priestley is often given priority because his work was published first. The name oxygen was coined in 1777 by Antoine Lavoisier, whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion.

Oxygen is a highly reactive element and is capable of combining with most other elements. It is required by most living organisms and for most forms of combustion. Impurities in molten pig iron are burned away with streams of high pressure oxygen to produce steel.

Oxygen can also be combined with acetylene (C2H2) to produce an extremely hot flame used for welding. Liquid oxygen, when combined with liquid hydrogen, makes an excellent rocket fuel. Ozone (O3) forms a thin, protective layer around the earth that shields the surface from the sun’s ultraviolet radiation. Oxygen is also a component of hundreds of thousands of organic compounds.

OXYGEN AS A LIQUID

Liquid Oxygen is one of the physical forms of elemental oxygen. It is abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries. 

The first measurable quantity of liquid oxygen was produced by Polish professors Zygmunt Wróblewski and Karol Olszewski (Jagiellonian University in Kraków) on April 5, 1883.

PHYSICAL PROPERTIES OF LIQUID OXYGEN. 

Some of the physical Properties of Liquid Oxygen are;

1. Liquid oxygen has a pale blue color.                                                                   2. It is strongly paramagnetic; it can be suspended between the poles of a powerful horseshoe magnet.                                                                          3.  Liquid oxygen has a density of 1.141 g/cm3 (1.141 kg/L or 1141 kg/m3) 4.  4. It is cryogenic with a freezing point of 54.36 K (−218.79 °C; −361.82 °F) and a boiling point of 90.19 K (−182.96 °C; −297.33 °F) at 101.325 kPa (760 mmHg).                                                                                                                    5.Liquid oxygen has an expansion ratio of 1:861 under 1 standard atmosphere (100 kPa) and 20 °C (68 °F) and because of this, it is used in some commercial and military aircraft as transportable source of breathing oxygen.

Key Point:    cryogenics is the study of the production and behaviour of materials at very low temperatures.       

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ELECTROLYSIS

Electrolysis is a technique that uses a direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is also important as a stage in the separation of elements from naturally occurring sources such as ores using an electrolytic cell.

It also refers to the decomposition of a substance by an electric current. The electrolysis of sodium and potassium hydroxides, first carried out in 1808 by Sir Humphrey Davey, led to the discovery of these two metallic elements and showed that these two hydroxides which had previously been considered un-decomposable and thus elements, were in fact compounds

Electrolysis of molten alkali halides is the usual industrial method of preparing the alkali metals:

cathode:
Na+ + e → Na(l) = –2.71 v
anode:
Cl → ½ Cl2(g) + e = –1.36 v
net:
Na+ + Cl → Na(l) + ½ Cl2(g) = –4.1 v

 

Ions in aqueous solutions can undergo similar reactions. Thus if a solution of nickel chloride undergoes electrolysis at platinum electrodes, the reactions are

cathode:
Ni2+ + 2 e → Ni(s) = –0.24 v
anode:
2 Cl → Cl2(g) + 2 e = –1.36 v
net:
Ni2+ + 2 Cl → Ni(s) + Cl2(g) = –1.60 v

 

 

FARADAY’S LAWS OF ELECTROLYSIS

First law of electrolysis

In 1832, Michael Faraday reported that the quantity of elements separated by passing an electric current through a molten or dissolved salt is proportional to the quantity of electric charge passed through the circuit. This became the basis of the first law of electrolysis:

m = k \cdot q

or

m = eQ

where; e is known as electrochemical equivalent of the metal deposited or of the gas liberated at the electrode.

Second law of electrolysis

Faraday discovered that when the same amount of current is passed through different electrolytes/elements connected in series, the mass of substance liberated/deposited at the electrodes is directly proportional to their equivalent weight.

 

WHAT HAPPENS TO COPPER DURING ELECTROLYSIS:

Positively charged ions move to the negative electrode during electrolysis. They receive electrons and are reduced. Negatively charged ions move to the positive electrode during electrolysis.

 

PROBLEMS AND SOLUTIONS ON ELECTROLYSIS:

PROBLEM 1.

A metallic object to be plated with copper is placed in a solution of CuSO4.

a) To which electrode of a direct current power supply should the object be connected?
b) What mass of copper will be deposited if a current of 0.22 amp flows through the cell for 1.5 hours?

Solution:

a) Since Cu2+ ions are being reduced, the object acts as a cathode and must be connected to the negative terminal (where the electrons come from!)

b) The amount of charge passing through the cell is

(0.22 amp) × (5400 sec) = 1200 c
or
(1200 c) ÷ (96500 c F–1) = 0.012 F

Since the reduction of one mole of Cu2+ ion requires the addition of two moles of electrons, the mass of Cu deposited will be

(63.54 g mol–1) (0.5 mol Cu/F) (.012 F) = 0.39 g of copper.

PROBLEM 2.

How long must a 20.0 amp current flow through a solution of ZnSO4 in order to produce 25.00 g of Zn metal.

Solution:

  • Convert the mass of Zn produced into moles using the molar mass of Zn.

Mass of Zn = 25.00g, molarmass of Zn = 65gmol-1

Mole = mass/molarmass

Mole = 25/65 = 0.3846mol

  • Write the half-reaction for the production of Zn at the cathode.

Zn2+(aq) + 2e  Zn(s)

  • Calculate the moles of e required to produce the moles of Zn and convert the moles of electrons into coulombs of charge using Faraday’s constant.

1 mole of Zn liberate 2F (2 x 96500)C

0.386 mole will liberate: (2 x 96500 x 0.3846/1) = 74231C

  • Calculate the time using the current and the coulombs of charge.

Q = I x t

t = Q / I

t = 74231/20

t = 3712secs = 62 minutes = 1.03hr

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CHEMICAL REACTION

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between
atoms , with no change to the nuclei (no change to the elements present), and can often be described by a chemical equation.

The substance (s) initially involved in a chemical reaction are called
reactants or reagents. Chemical reactions are usually characterized by a chemical change , and they yield one or more products , which usually have properties different from the reactants.

NOTE: Antoine Lavoisier developed the theory of combustion as a chemical reaction with oxygen.

The general equation for a reaction is:
REACTANT + REACTANT = PRODUCT + PRODUCT
For example; When sulfur dioxide is added to oxygen, sulfur trioxide is produced. In the chemical equation shown below, sulfur dioxide and oxygen (SO 2 and O2 ) are reactants, and sulfur trioxide (SO 3 ) is the product.
It can be represented mathematically as;
2SO2 + O2 > 2SO3

TYPES OF CHEMICAL REACTION
Some types of Chemical reactions are;
1. •Direct Combination or Synthesis Reaction
In a synthesis reaction two or more chemical species combine to form a more complex product.
A + B → AB
The combination of iron and sulfur to form iron (II) sulfide is an example of a synthesis reaction:
8 Fe + S8 → 8 FeS

2. Oxidation-Reduction or Redox Reaction
In a redox reaction the oxidation numbers of atoms are changed.
Redox reactions may involve the transfer of electrons between chemical species.
The reaction that occurs when In which I2 is reduced to I- and S2O32- (thiosulfate anion ) is oxidized to S4O62- provides an example of a redox reaction :
2 S2O32−(aq) + I2(aq) → S4O62−(aq) + 2 I−(aq)

NOTE: Rust Is a Common Chemical Reaction

3. •Acid-Base Reaction
An acid-base reaction is type of double displacement reaction that occurs between an acid and a base. The H+ ion in the acid reacts with the OH- ion in the base to form water and an ionic salt:
HA + BOH → H2O + BA
The reaction between hydrobromic acid (HBr) and sodium hydroxide is an example of an acid-base reaction:
HBr + NaOH → NaBr + H2O

FACTORS THAT AFFECT RATE OF REACTION:
The following are factors that affect the rate of a reaction;
Concentration of Reactants, Temperature, Presence of Catalysts and Competitors, State of Matter, Pressure and Mixing reactants together increases their ability to interact, thus increases the rate of a chemical reaction.

Reference: Wikipedia,chemistry.about.com, ck12.org

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