(5) Oxygen and Hydrogen

Chaps 7-8

What is true about oxygen?

-Most abundant element on earth
-21% of the atmosphere
-89% of the mass of water
-Acid former is what it means
-Highly electronegative

What are the physical properties of oxygen?

-Colorless, odorless and tasteless gas
-Heavier than air
-Slightly soluble in water
-Can be liquified and solidified by extreme pressure at low temperatures

What are the chemical properties of oxygen?

-Reacts with many substances slowly at ordinary temperatures, but rapidly at high temperatures
-Reacts with many metallic and nonmetallic elements to form oxides
-Supports combustion
-Acts as an oxidizing agent

What is the historical/classical method of preparing oxygen?

heating mercuric oxide which separates the oxygen from the mercury

What is the laboratory method of preparing oxygen?

A mixture of potassium chlorate and manganese dioxide is heated, resulting in oxygen, potassium, chloride and manganese dioxide

What are the commercial methods of preparing oxygen?

-Evaporation of liquid air at -200C
-Application of an electric current to water

What is a catalyst?

-A substance that speeds up a chemical reaction yet appears in unchanged form among the products of the reaction
-Lowers the amount of energy necessary for a reaction to occur

How does temperature affect a reaction?

-there is a direct relationship between temperature and the speed of a chemical reaction
-reaction rates increase at higher temperatures and decrease at lower temperatures

How does physical state affect reaction rates?

(This refers to the size of the particles of the reacting substance)
-influences physical as well as chemical changes
-The smaller the particle size, the alrger the surface area

How does concentration affect reaction rates?

-Rates of chemical reactions are proportional to the molecular concentration of the reacting substances
-The greater the concentration, the faster the reaction
-The lower the concentration, the slower the reaction

How does light affect reaction rates?

Many chemicals reactions are caused or accelerated by light, or photochemical means

How does pressure affect reaction rates?

-Very little effect on chemcial reactions other than those involving gases
-Reaction between gaseous reactants are accelerated by an increase in pressure and slowed by a decrease in pressure

Oxygen is an allotropic molecule, which means

it has 3 forms

What are the 3 forms of oxygen?

1: Ozone (o3, unstable)
2: Molecular oxygen (o2, stable)
3: Nascent oxygen (O, unstable)

What is ozone?

-Formed by passing a high voltage discharge through oxygen
-Pale blue colored gas
-Penetrating odor
-More chemically active than oxygen, but less stable
-Readily decomposes, liberating nascent oxygen
-Has bleaching and deodorizing qualities due to high oxidizing abilities
-Good for treating drinking and waste water
-Disinfecting swimming pools
-Used in home air purifiers
-Its use is limited as it has a toxic and unstable nature
-A true deodorant ebcause it literally destroys odor

What is important to know about hydrogen?

-Most abundant element in the universe
-Hydrogen typically appears in the combined state and may be found in acids, bases, water, plant and animal tissues and natural gases
-The free form of hydrogen exists in the earth’s crust and is released during volcanic erruptions
-Homonuclear like oxygen and is typically a diatomic molecule

What are the physical properties of hydrogen?

-Colorless, odorless and tasteless gas|
-Lighter than air- the lightest gas known
-Slightly solubel in water
-Highly diffisuble

What are the chemical properties of hydrogen?

-Burns with a hot, blue flame and then form water; usually an explosion
-Does not support combustion (pure hydrogen will extinguish a flame)
-Acts as a reducing agent (eagerly adds itself to other substances)

What is the commerical method of preparing hydrogen?

electrolysis of water

What is the laboratory method of obtaining hydrogen?

Addition of a dilute solution of hydrochloric acid to zinc