C2- exam questions

Question 1

Explain why graphite is:
* a good electrical conductor
* soft and slippery
You should answer in terms of structure and bonding. (6)

Answer 1

• graphite is a giant structure with three covalent bonds per carbon atom
• only three electrons per carbon atom used in (covalent) bonds
• so one electron per carbon atom (is delocalised)
• these delocalised electrons can move through the structure
• carrying (electrical) charge so graphite conducts electricity
  soft and slippery:
  no (covalent) bonds between layers
• so the layers can slide over each other
• so graphite is soft and slippery

Question 2

Explain why the reactivity of elements changes going down Group 1. (4)

Answer 2

• reactivity increases (going down the group)
• (because) the outer electron / shell is further from the nucleus
• (so) there is less attraction between the nucleus and the outer electron / shell
• so the atom loses an electron more easily

Question 3

Explain why sodium oxide has a high melting point.

Answer 3

• giant structure
• (with) strong (electrostatic) forces of attraction between (oppositely
  charged) ions
• (so) large amounts of energy are needed to break the bonds / forces

Question 4

Describe what happens when a lithium atom reacts with a chlorine atom.
Answer in terms of electrons (4)

Answer 4

lithium (atom) loses (one) electron(s)
chlorine (atom) gains (one) electron(s)
reference to transfer of one electron
to form positive and negative ions

Question 5

Explain why nitrogen is a gas at room temperature. (3)

Answer 5

• weak intermolecular forces
• between molecules
• (which) need little energy to overcome

Question 6

Suggest why Buckminsterfullerene is a good lubricant (2)

Answer 6

molecules are spherical
(so molecules) will roll

Question 7

Silver nanoparticles are sometimes used in socks to prevent foot odour.
Suggest why it is cheaper to use nanoparticles of silver rather than coarse
particles of silver(2)

Answer 7

• (nanoparticles) have a larger surface area to volume ratio
• so less can be used for the same effect

Question 8

Potassium forms an ionic compound with sulfur.
Describe what happens when two atoms of potassium react with one atom
of sulfur.
Give your answer in terms of electron transfer.
Give the formulae of the ions formed.(5)

Answer 8

• electrons transferred from potassium to sulfur
• two potassium atoms each lose one electron
• forming K+
• sulfur atoms gain 2 electrons
• forming S2−

Question 9

The ball and stick model is not a true representation of the structure of
potassium sulfide.
Give one reason why. (1)

Answer 9

there are no gaps / sticks between the potassium ions and sulfide ions

Question 10

Sodium fluoride is an ionic substance.
What are two properties of ionic substances

Answer 10

Dissolve in water
1
High melting point

Question 11

Explain why this alloy is harder than the pure metal Y. (2)

Answer 11

• the atoms / particles / ions are different sizes
• so there are no rows / layers to slid

Question 12

Describe a safe method for making pure crystals of copper sulfate from copper carbonate
and dilute sulfuric acid. Use the information in the figure above to help you.

Answer 12

sulfuric acid in beaker (or similar)
* add copper carbonate one spatula at a time
* until copper carbonate is in excess or until no more effervescence occurs *
* filter using filter paper and funnel
* filter excess copper carbonate
* pour solution into evaporating basin / dish
* heat using Bunsen burner
* leave to crystallise / leave for water to evaporate / boil off water
* decant solution
* pat dry (using filter paper)
* wear safety spectacles / goggles

Question 13

Give one reason why is it important for the percentage atom economy of a reaction to be as high as possible (1)

Answer 13

• important for sustainable development
• Economic reasons
• Waste products may be pollutants / greenhouse gases