C5- Chemicals Of The Natural Environment

Question 1

Covalent bonds- sharing electrons?

Answer 1

Atoms make covalent bonds by sharing electrons with other atoms. Then both atoms have a full outer shell.

Each covalent bond provides one extra shared electron for each atom.

Each atom involved has to make enough covalent bonds to fill up its outer shell.

The atoms bond due to the electrostatic attraction between the positive nuclei and the negative electrons shared between them.

Question 2

What is the earths hydrosphere??

Answer 2

The earths hydrosphere consists of all the water in the oceans,seas,lakes,rivers and puddles.

Also it contains the compounds that are dissolved in the water. Many of these compounds are ionic compounds called salts.

Question 3

Solid ionic compounds?

Answer 3

• Ionic compounds are made of charged particles called ions.
• Ions with opposite charges are strongly attracted to one another.
• You get a massive giant lattice of ions built up.
• There are very strong chemicals bonds called ionic bonds between all the ions.
• A single crystal of salt is one giant ionic lattice.

Question 4

Melting and boiling points of ionic compounds?

Answer 4

• The forces of attraction between the ions are very strong.
• It takes a lot of energy to overcome these forces and melt the compound. And even more energy to boil it.
• Ionic compounds have high melting and boiling points which make them solid at room temperature.

Question 5

What happens when an ionic compound dissolves?

Answer 5

• The ions separate and are free to move in the solution.
• This means they can carry an electric current.
• When ionic compounds melt the ions are free to move. So they carry an electric current.
• When an ionic compound is solid the ions aren’t free to move and so an electric current can’t pass through the substance.

Question 6

Describe molecular substances?

Answer 6

• They usually exist as small molecules.
• The atoms within the molecules are held together by very strong covalent bonds.
• The forces of attraction between these molecules are very weak.
• You only need a little bit of energy to overcome the weak forces between the molecules. So molecular substances have low melting and boiling points.
• They are usually gases and liquids at room temperature.
• They don’t conduct electricity as their molecules aren’t charged.
• There are no free electrons or ions.

Question 7

What is a flame test?

Answer 7

Compounds of some metals give a characteristic colour when heated. This is the idea behind flame tests.

Question 8

Flame test results?

Answer 8

• Sodium gives orange/yellow flame.
• Potassium gives a lilac flame.
• Calcium gives a brick red flame.
• Copper gives blue green flame.

You can use these colours to detect and identify different ions.

Question 9

What is a precipitation reaction?

Answer 9

Is where two solutions react to form an insoluble solid compound called a precipitate.

Question 10

Sodium hydroxide test?

Answer 10

Metal hydroxides are insoluble and precipitate out of the solution when you add an alkali.

Hydroxides have a characteristic colour. If you put few drops of sodium hydroxide solution to the mysterious compound.

You will hopefully make an insoluble hydroxide.

Question 11

Hydrochloric acid test?

Answer 11

With dilute Hydrochloric acid, carbonates will fizz because they give off carbon dioxide.

You can test for carbon dioxide using limewater.

CO2 turns limewater cloudy. Of the water goes cloudy you have identified a carbonate ion.

Question 12

Testing for sulfates?

Answer 12

To identify a sulfate ion add dilute HCL followed by barium chloride solution.

A white precipitate of barium sulfate means the original compound was a sulfate.

The Hydrochloric acid is added to get rid of any traces of carbonate ions before you do the test.

As this would produce a precipitate and it would confuse the results.

Question 13

Testing for halides?

Answer 13

To identify a halide ion add dilute nitric acid followed by silver nitrate solution.

A chloride gives a white precipitate of silver chloride.

A bromide gives a cream precipitate of silver bromide.

An iodide gives a yellow precipitate of silver iodide.

Nitric acid is added to get rid of carbonate ions before the test.

Question 14

What is the earths lithosphere?

Answer 14

It is the earths rigid outer layer - the crust and part of the mantle below it.

It is made from a mixture of minerals containing silicon, oxygen and aluminium.

Question 15

What does carbon form?

Answer 15

Carbon can form two types of giant covalent structures - diamond and graphite.

Diamond and graphite are minerals which are found in the earths crust.

Question 16

Diamond?

Answer 16

• The carbon atoms in diamond each form 4 covalent bonds in a very rigid giant covalent structure.
• This structure makes the diamond the hardest natural substance.
• The strong covalent bonds give diamond a very high melting point.
• It doesn’t conduct electricity because it has no free electrons.
• Its insoluble in water.

Question 17

Graphite?

Answer 17

• It is made from carbon.
• Each carbon atom forms 3 covalent bonds creating sheets of carbon atoms which are free to slide over each other. So it is useful for lubricant.
• They layers are held together so loosely that they can be rubbed off.
• It has a high melting point- the covalent bonds need loads of energy to break.
• There are lots of spare electrons. This means they can conduct electricity - it’s used for electrodes.

Question 18

Silicon dioxide??

Answer 18

• Most of the silicon and oxygen in the Earths crust exists in the compound silicon dioxide.
• Silicon dioxide is what sand is made of.
• Each grain of sand is one giant structure of silicon and oxygen.
• It doesn’t conduct electricity
• It has a high melting point.

Question 19

What are rocks made of?

Answer 19

Minerals

Question 20

What are minerals?

Answer 20

They are solid elements and compounds.

Question 21

What are metal ores?

Answer 21

They are rock that contain varying amounts of minerals from which metals can be extracted.

Question 22

Where is gold found?

Answer 22

A few unreactive metals like gold are found in the Earth as the metal itself- rather then a compound.

Question 23

How are most metals extracted?

Answer 23

They can be extracted from their ores using a chemical reaction.

Question 24

Why are some metals harder to extract?

Answer 24

More reactive metals like sodium are harder to extract. This is why they take longer to discover it.

Question 25

How can metals be extracted by reduction?

Answer 25

Extracting a metal from its ore is chemical reduction using carbon or carbon monoxide.

When an ore is reduced oxygen is removed from it.

When a metal oxide loses its oxygen it is reduced. The carbon gains the oxygen and is oxidised.

How reactive the metal is compared to carbon determines whether it can be extracted by reduction with carbon or carbon monoxide.

Question 26

What is electrolysis?

Answer 26

It is the decomposition of substances using electricity.

Question 27

What is electrolyte?

Answer 27

Electrolysis needs a liquid to conduct electricity called electrolyte.

Electrolytes are free ions dissolved in water or molten ionic compounds.

It is the free ions that conduct the electricity.

Question 28

What happens in electrolysis?

Answer 28

Electrons are taken away from ions at the positive electrode and given to other ions at the negative electrode. As ions gain or lose electrons they become atoms or molecules.

Question 29

How does electrolysis remove aluminium?

Answer 29

• The main ore of aluminium is bauxite which contains aluminium oxide.
• Molten aluminium oxide contains free ions so it’ll conduct electricity.
• The positive ions are attracted to the negative electrode where they pick up three electrons and they turn into neutral aluminium atoms. These then sink to the bottom.
• The negative ions are attracted to the positive electrode where they lose two electrodes. The neutral oxygen atoms will then combine to form dioxide molecules.

Question 30

Decomposition of aluminium oxide equations?

Answer 30

Aluminium oxide → aluminium + oxygen

Question 31

What are metals made of?

Answer 31

Metals consists of a giant structure.

Question 32

What are metallic bonds?

Answer 32

Metallic bonds involve the free electrons which produce all the properties of metals.

These free electrons come from the outer shell of every metal atom in the structure.

The positively charged metal ions are held together in a crystal by a sea of free electrons that can move.

Question 33

What do free electrons carry?

Answer 33

The free electrons carry both heat and electrical current through the material so metals are good conductors of heat and electricity.

Question 34

Metals strong and malleable?

Answer 34

Metallic bonds means metals have high tensile strength.

The layers of atoms in a metal can slide over each other making metals malleable- they can be hammered or rolled into flat sheets.

Question 35

Metals have high melting and boiling points?

Answer 35

Metallic bonds are very strong so it takes a lot of energy to break them.

You have to get the metal very hot to melt it.

Question 36

Benefits of ores and mining?

Answer 36

• Ores are finite resources
• Mining metal ores is good as useful products can be made.
• Mining provides people with local jobs.
• Mining brings money to the area, this means health and transport can be improved.

Question 37

Disadvantages of ores and mining?

Answer 37

• Mining ores is bad for the environment as it uses lots of energy.
• It scars the landscape.
• It destroys habitats.
• Noise,dust and pollution are caused by increased traffic.
• Deep mine shafts can be dangerous after the mine is abandoned.

Question 38

Recycling metals?

Answer 38

• Recycling metals only uses a small fraction of the energy needed to mine and extract new metal.
• Recycling saves money.
• There are finite amount of metals - recycling conserves these resources.
• It reduces the amount of rubbish sent to the landfill.