OZ From Sep 2015

Question 1

What are the two most chemically important regions in the atmosphere?

Answer 1

The troposhere and the stratosphere.

Question 2

State the main gases in unpolluted air.

Answer 2

Nitrogen Oxygen Argon

Question 3

Why does increased mass normally lead to increased Boiling Point?

Answer 3

More mass means more protons (and so more electrons). The more electrons, the more likely to have uneven distribution of electrons. Uneven distribution of electrons causes instantaneous dipoles to form.

Question 4

Why does branching of alkanes normally lower Boiling Point?

Answer 4

Branched alkanes pack less closely together, so the intermolecular forces are weaker.

Question 5

What features must be present in a molecule for Hydrogen bonding to occur?

Answer 5

1. A Hydrogen atom covalently bonded to either N, O or F.
2. That Hydrogen atom must be free to get close to N, O or F in a neighbouring molecule
3. A lone pair of electrons on a N, O or F that can line up with the Hydrogen atom mentioned in “1”

Question 6

Draw a Hydrogen bond in water

Answer 6

Question 7

Explain whether or not the molecule of CF₃Cl is polar. (2 marks)

Answer 7

It is polar because the C-Cl bond is less polar than the C-F bond. This means the charges do not cancel out.

Question 8

What happens when ₉₀ ²²⁸Th gives out alpha radiation?

Answer 8

₈₈²²⁴Ra+₂⁴ H