C5 - Chemicals of the Natural Environment

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  • Created by: hollych
  • Created on: 01-12-16 11:43
Earth's atmosphere contains many
Gasses
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What are the quantities of the main gases in the atmosphere?
78% nitrogen, 21% oxygen, 1% argon, 0.04% CO2
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What sized molecules do molecular sunstances usually exist as?
small molecules
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What type of elements and compounds are molecular?
Most non-metal ones
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Why do molecular substances have low melting and boiling points?
They have weak intermolecular forces, so only a small amount of energy is needed to break them.
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Why can't pure molecular substances conduct electricity?
Because they their molecules aren't charged - no free electrons.
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What is covalent bonding?
The sharing of electrons with other atoms to complete their outer electron shells.
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How do the atoms bond?
The electrostatic attraction between the positive nuclei and negative electrons bond them.
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Describe the difference between a double bond and a single bond?
A single bond is where just one electron is shared to complete the atom's outer shells. In a double bond the atoms need two atoms to complete their outer shells, so they share two pairs of electrons.
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Give an example of a molecule bonded in each way.
A diatomic hydrogen molcule. A carbon dioxide molecule.
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What is the hydrosphere?
All the Earth's water, and any compounds dissolved in it.
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What are ionic compounds called?
Salts
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Why do solid ionic compounds form crystals?
Because of the strong ionic bonds between the ions, the ions form a lattice.
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Why do ionic compounds have high melting and boiling points?
The forces between the ions are very strong, so it takes a lot of energy to break these forces.
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Given this, what state are ionic compounds at room temerature?
solid.
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When can an ionic compound conduct electricity?
When it is dissolved in water or when it is molten.
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How?
The ions seperate meaning the ions are free to move around, and can therefore carry an electrical current.
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How can you test for positive ions?
A flame test, or adding sodium hydroxide to a solution.
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How does a flame test work?
When some metals are heated, they produce a coloured flame. Sodium gives an orange/ yellow flame, potassium - lilac, calcium - red, copper - bluey green.
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How does a sodium hydroxide test work?
Most metal hydroxides are insoluble and form precipitates in water. When sodium hydroxide is added to a solution the sodium displaces the metal and a metal hydroxide precipitate is formed.
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What colour precipitates are formed?
Ca2 + is white, Cu2+ is blue, Fe2+ is sludgy green, Fe3+ is reddish brown, Zn2+ is white at first but dissolves in excess sodium hydroxide.
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What is the difference between an ionic equation and a full equation?
Ionic equations only show the reactants and products which don't appear on both sides of the equation, and aren't relevant to the reaction.
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How can you test for negative ions?
Hydrochloric acid can detect carbonates, because when the two react they give off carbon dioxide. You can test for sulfates with HCl and Barium chloride - the HCl gets rid of any carbonates, and if a white precipitate forms when the BaCl is added...
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cont.
then the compound was a sulfate as the white precipitate is Ba sulfate. You can identify halide ions by adding nitric acid then silver nitrate. A chloride gives a white precipitate (of silver chloride) , a bromide gives a cream, and iodide yellow.
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What is the lithosphere?
The Earth's outer layer.
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What tyoe of structure does carbon form?
A giant convalent structure.
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List the properties of diamond.
Rigid, hard, strong covalent bonds, high melting point, insoluble in water, insulator of electricity.
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List the properties of graphite.
Carbon atoms only form 3 covalent bonds so there are sheets of c atoms, these can slide over eachother, strong covalent bonds, high melting point, Spare elctrons conduct electricity.
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What is silicon dioxide?
A giant covalent structure that makes up most of Earth's crust. It is also called silica and is basically sand. Similar structure and properties to diamond.
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Explain what a metal ore is.
rocks which contain varying amounts of minerals from which, metals can be extracted.
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Why do large amounts of ores usually need to be obtained?
Because they only contain a small amount of metal. Eg copper mining.
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Name 2 examples of metal ores.
Iron ore - haematite, Copper ore - Chalcopyrite.
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How are most metals extracted?
Through a chemical reaction.
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Which types of metals are harder to extract?
More reactive metals as they are found as a number of compounds.
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How are metals which are less reactive than carbon extracted?
Through a reduction reaction, where carbon/carbon monoxide is oxidised and the metal is left alone.
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How are metals which are more reactive extracted?
electrolysis.
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What does electrolysis need to work?
An electric current which passes through an electrolyte (molten salts or dissolved salts). The anode takes the electrons away from the ions, and the cathode gives them electrons.
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How does electrolysis work to extract aluminium ffom bauxite?
Molten aluminium oxide is the elecrolyte as is conducts electricity. The positive metal ions are attracted to the cathode and the oxygen ions are negative so attracted the anode.
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What is the relative atomic mass?
How heavy an atom is compared to the mass of carbon - exactly 12.
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How can you find how much metal is in an ore?
Calculateing the percentage of the metal mass in the relative formula mass and multiplying this by the mas of copper oxide.
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List the properties of metals.
free electrons, conductors of heat and electricity, high tensile strength, malleable, usually have high melting and boiling points.
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What type of resource are ores?
Finite resources.
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Why is recycling metals important?
You don't need to mine them which wastes energy and money. Mining also destroys habitats. Metal not sent to landfill. Conserves earth's natural resources.
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Card 2

Front

What are the quantities of the main gases in the atmosphere?

Back

78% nitrogen, 21% oxygen, 1% argon, 0.04% CO2

Card 3

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What sized molecules do molecular sunstances usually exist as?

Back

Preview of the front of card 3

Card 4

Front

What type of elements and compounds are molecular?

Back

Preview of the front of card 4

Card 5

Front

Why do molecular substances have low melting and boiling points?

Back

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