C5 - Chemicals of the Natural Environment

Question 1

Compare the structure of Diamond and Graphite.

Answer 1

• In diamond, each carbon atom is covalently bonded to four other carbon atoms.
• In graphite, each carbon atom is covalently bonded to three other carbon atoms.
• In graphite, there is weak intermolecular forces. This is because it is in layers, which slide off each-other and are therefore soft. In between the layers are excess, free electrons, therefore it can conduct electricity.

Question 2

What are the properties of Silicon Dioxide?

Answer 2

Silicon dioxide is present in the lithosphere and is a giant covalent, so it has properties similar to diamond.

Silicon dioxide has the following properties:

• Hard.
• High melting point.
• Does not conduct electricity.
• Insoluble in water.

Question 3

Explain why ionic compounds do not conduct electricity until molten or dissolved.

Answer 3

Because the ions are not free to move.

When molten, the ions are released from the lattice and in water, the water molecules will deattach ions from the lattice (They are polar and have a positive and negative end).

Question 4

When is electrolysis used?

Answer 4

When metals are too reactive to be extracted by heating with carbon.

Question 5

When aluminium is extracted via electrolysis, cryolite is added. Why is this?

Answer 5

Because cryolite lowers the melting point of the aluminium oxide, used in electrolysis.

Question 6

Why do metals conduct electricity?

Answer 6

Because they have a sea of electrons where the electrons are free to move.

Question 7

Why are metals malleable?

Answer 7

Because their ions are arranged in a lattice, where rows of ions can slide over each other.

Question 8

Explain the laboratory method of making Copper Sulphate Salt with copper oxide and hot sulphuric acid.

Answer 8

1. Add copper oxide to a volume of hot sulphuric acid.
2. Stir until the black powder won’t dissolve anymore.
3. Filter to get rid of any black powder and you will get a blue solution.
4. Evaporate excess water to be left with the copper sulphate crystals.

Question 9

Explain the test for negative ions with carbonates.

Answer 9

Add an acid, it should fizz with carbon dioxide and therefore turn limewater cloudy.

Question 10

Explain the test for negative ions with halides.

Answer 10

Add dilute nitric acid,

Then add silver nitrate.

Chlorine ions will turn white, Bromide ions will turn cream and Ioidide ions will turn yellow.

Question 11

Explain the test for negative ions with sulfates.

Answer 11

Add dilute HCl then BaCl₂ (Barium chloride).

If sulfate ions are present, a white precipitate will form.

Question 12

How do you calculate reacting mass?

e.g) Find the mass of Zn that can be extracted from 100g of ZnO.

Answer 12

1) Write down the formula.
2) Calculate the relative formula mass.
3) Work out the percentage mass of the metal.
4) Work out the mass of the metal.
e. g) Find the mass of Zn that can be extracted from 100g of ZnO.
1) ZnO.
2) RFM of ZnO = 65+16 = 81. RAM of Zn = 65.
3) Percentage of zinc present = 65/81 * 100 = 80%.
4) In 100g of ZnO, there will be 80/100 * 100 = 80g of Zn.

Question 13

What happens during the electrolysis of Al₂O₃?

Answer 13

As the positive anodes are made from carbon, CO₂ is produced as the negative O^2- ions go to the anodes.

The container acts as the negative cathode, and Al³⁺ is deposited here.

Question 14

What are the percentages of elements in the atmosphere?

Answer 14

• Nitrogen - 78%.
• Oxygen - 21%.
• Argon - 1%.
• Carbon dioxide - 0.04%.

Question 15

How are atoms held together in covalent bonds?

Answer 15

Because the positively charged nuclei of two atoms is attracted to the negatively charged pair of electrons.

Question 16

How can you tell if something is a gas at room temperature?

Answer 16

If it’s melting and boiling points are below 25^oC.

Question 17

Why do nitrogen and oxygen have such low melting and boiling points (-210, -196; -218, -183)?

Answer 17

Because they have very little attractive forces, due to their small atomic size.

Question 18

Why do pure molecular substances not conduct electricity?

Answer 18

Because they have no electrical charge.

Question 19

For small covalent molecules, the forces _______ molecules are weak, and the forces __________ molecules are strong.

Answer 19

For small covalent molecules, the forces between molecules are weak, and the forces within molecules are strong (Covalent bonds).

Question 20

What is a salt?

Answer 20

Any chemical compound formed from the reaction of an acid with a base, with all or part of the hydrogen of the acid replaced by a metal or other cation.

Question 21

What is a precipitate?

Answer 21

An insoluble solid that gets deposited.

Question 22

What sphere are rocks found in?

Answer 22

The lithosphere.

Question 23

State a way of removing metal oxides from ore.

Answer 23

Heating with carbon, to reduce the oxygen.

This is called a redox reaction.

This is because the metal oxide loses oxygen, and the carbon gains oxygen (Producing CO₂).

Question 24

Define electrolysis.

Answer 24

Passing an electric current through an ionic compound when it is either molten or dissolved in water.

Question 25

In electrolysis, what is the compound that conducts electricity called?

Answer 25

The electrolyte.