Chemicals of the Natural Environment. Flashcards
What does dry air contain?
A mixture of non metal elements and compounds eg N2, O2, Ar, CO2
What is Ar?
Argon, a noble gas.
What percentage of dry air is oxygen?
21%
What percentage of dry air is nitrogen?
78%
What percentage of dry air is argon?
1%
What percentage of dry air is carbon dioxide?
0.04%
How are the molecules in the air held together?
Covalent bonds.
How does a covalent bond form?
Atoms share a pair of electrons.
How does that hold the atoms together?
Both positive nuclei are attracted by the electron cloud between them.
What sort of boiling and melting points do simple molecules have?
Very low, eg N2 -210C and -196C
Why do these small molecules have such low melting and boiling points?
The attractive forces between the molecules are very weak, so very little energy is required for them to move apart.
Why can’t pure molecular substances conduct electricity?
They are electrically neutral, and there are no free electrons.
How strong are the forces within the molecules for these small molecules like O2?
Very strong.
What happens when a molecular substance melts?
The molecules are separated from one another, but the covalent bonds are not broken.
What is the name given to all the water on earth?
The earth’s hydrosphere
What does the hydrosphere consist of?
Mainly water, with some dissolved ionic compounds called salts.
How are the ions in an ionic solid arranged?
In a giant regular 3D pattern called a lattice.
What is the name given to the force of attraction between positive and negative ions?
Ionic bond
Why do ionic compounds not conduct electricity when they are solid?
The ions are not free to move.
Why do ionic compounds conduct electricity when in solution, or molten?
The ions are free to move.
Why would it be true to say that ionic compounds only exist in the solid state?
When they are liquid or aqueous the ions are all moving independently, they are not moving as a pair.
What is the overall charge on an ionic compound?
Neutral
What do you call an ion made up of a group of atoms, eg OH-
A molecular ion
What is the charge on the SO4 ion?
2-
What is the charge on the OH ion?
-
What is the charge on the CO3 ion?
2-
What is the charge on the NO3 ion?
-
What colour are many salts of copper when in solution?
Blue
How can an insoluble precipitate be used to identify an ionic compound?
The colour of the precipitate can be distinctive.
What happens if you add sodium hydroxide to a calcium salt?
You get a white precipitate (insoluble in excess)
What happens if you add sodium hydroxide to a copper salt?
You get a light blue precipitate (insoluble in excess)
What happens if you add sodium hydroxide to an iron (II) salt?
You get a green precipitate (insoluble in excess)
What happens if you add sodium hydroxide to an iron (III) salt?
You get a red-brown precipitate (insoluble in excess)
What happens if you add sodium hydroxide to a zinc salt?
You get a white precipitate (soluble in excess)
How could you identify the carbonate ion?
Add dilute acid and look for effervescence (fizzing)
What is the name for the outer layer of the earth, made up of the crust and upper mantle?
The lithosphere.
What is the lithosphere made of?
Rocks and minerals
What are minerals?
Solids with ions or atoms arranged in a regular structure or lattice.
What are the abundant elements in the lithosphere?
Silicon, oxygen, aluminium
Where are most of the silicon and oxygen on earth found?
Joined together as SO2 in rocks, eg quartz
What is a rock containing a metal called?
An ore
How can you extract the metal if the metal ore is an oxide?
Copper, zinc and iron are all heated with carbon, which reduces the metal by taking away the oxygen
How much metal is there in an ore?
It varies, sometime huge amounts of ore give only small amounts of metal - eg copper.
What sort of reaction is the heating of metal oxide with carbon?
Redox, as both reduction and oxidation happen
What is reduction?
Losing oxygen
What is oxidation?
Gaining oxygen
What element makes up diamond and graphite?
Carbon
What is the structure of both diamond and graphite?
Many carbon atoms are bonded together in a regular pattern.
What would you call it when many atoms are covalently bonded together in a regular structure?
A giant covalent structure.
What is the shape of the lattice in diamond?
Each carbon atom is surrounded by 4 other carbon in the shape of a tetrahedron, this is a very strong structure.
What is the shape of the lattice in graphite?
The carbon is arranged in hexagons, which form layers. This structure breaks easily along the layers. (And conducts electricity).
Why does graphite conduct electricity?
There are free moving electrons between the layers of hexagons.
Which is the only covalently bonded substance that can conduct electricity?
Graphite.
What do you call the chemicals that react together?
The reactants.
What do you call the chemicals that are made?
The products.
What does a chemical equation show?
The reactants and the products.
What does a balanced chemical equation show?
The numbers of atoms on each side of the equation, these must be equal.
What do the state symbols show?
The state of each of the substances, solid (s), liquid (l), gas (g), or dissolved in water (aq)
What is the relative atomic mass of an atom?
The mass of an atom compared to an atom of carbon 12, which is given the value of 12.
What is the relative formula mass of a compound?
The sum of the relative masses of all of its atoms or ions.
What is the gram formula mass of a compound?
The relative formula mass in grammes. So, for water, H2o, we add up 1+1+16 = 18, so 18g
How can you work out the percentage of an element in a compound?
Take the relative mass of the element, divide by relative mass off the compound, then multiply by 100
What is the percentage iron in Fe2O3 (use your periodic table)?
70%
How much iron can you get from 160 grammes of Fe2O3?
112g
What does the word electrolysis mean?
Splitting with electricity - used to mean passing an electric current through a solution of an ionic compound, or a molten ionic compound, and splitting it.
Why is the ionic compound called an electrolyte?
because it conducts electricity and splits.
How can you make aluminium from aluminium oxide?
Electrolysis
What is produced at the anode when aluminium oxide is electrolysed?
Oxygen
Why does aluminium oxide need to be electrolysed rather than using a redox reaction with carbon?
Carbon can’t take the oxygen from aluminium, the aluminium is too reactive.
How many electrons would the Al3+ ion gain?
3
How many electrons would each O2- ion lose?
2
Is aluminium a cation or an anion?
Cation
Why are metals useful?
They are strong, malleable (they can be hammered into shape), have high melting points and can conduct electricity.
What bonds hold the atoms in metals together?
Metallic bonds
How are the atoms in metals arranged?
In a giant lattice
What do metals lose to form ions?
Their outer shell electrons.
What happens to the electrons in solid metals?
They form a “sea of electrons” which can move freely
Is the attraction between the positive atoms and the sea of electrons strong or weak? (Hint - think about the melting point of metals)
Strong
In a pure metal, all the atoms are the same size. True or false?
True
When a metal is reshaped, what do the atoms do?
Roll over each other.
Metal is easily reshaped, the word for this is?
Malleable
What property of metals can make them very dangerous to the environment?
They are poisonous, eg lead, mercury, cadmium.
What do waste poisonous metals from mines do?
Destroy habits, damage soil, pollute water sources.
What does extracting metal create that causes acid rain?
Pollutant gases
Large amounts of some ores need to be processed to get very small amounts of metal. True or false?
True
Processing large amounts of rock requires large amounts of ….?
Energy
If the ore contains a compound of metal and sulfur, what pollutant is likely to be made during the extraction of the metal?
SO2
What does SO2 form with water?
H2SO3 (sulfurous acid)
What water would SO2 in the atmosphere react with?
Rain
What would be the pH of rain that contains H2SO3?
Less than 7, acid
Why do we need large amounts of copper?
It is used for electrical wiring (very low resistance) and water pipes.
What poisonous metals did car batteries once contain?
Pb (lead)
What metal does modern batteries contain?
Lithium
Why is using lithium in batteries a problem?
It is hard to get enough lithium
