CHEMISTRY: EDEXCEL IAL UNIT 2 - PAST PAPER QUESTIONS

How is the bonding in gaseous hydrogen halides best described as?

mainly covalent with an increasing tendency towards ionic as you go up the group

what would be the colour of the solution when iodine is dissolved in a hydrocarbon solvent?

purple

Explain how 2-methylpropan-2-ol is formed from 2-chloro-2-methylpropane. Describe the role of water in this case.

1) water acts as a nucleophile/ water can donate a lone pair (from oxygen).

2) and attack (+ve) carbon (originally attached to Cl)/bonds to carbon/ bonds to the carbocation.

Explain how 2-methylpropene is formed from 2-chloro-2-methylpropane. Describe the role of water in this case.

1) the OH- ion in water behaves as a base.

2) and accepts a hydrogen ion/ proton/ removes a hydrogen ion.

Suggest why 1-chlorobutane reacts via a different mechanism with water than 2-chloro-2-methylpropane.

1) butyl group less electron releasing/ has less of a (positive) inductive effect.

2) so less stale (positive charge on) carbocation.

OR

1) 1-chlorobutane is primary halogenoalkane.

2) so forms a less stable carbocation.

OR

1+2) primary carbocation is less stable than secondary carbocation.

Suggest why 2-flouropropane would react more slowly than 2-chloropropane.

What reagent would be used instead of water to increase the ROR (2-flouropropane)? Explain why the reagent would have this effect.

1) C-F bond is stronger than C-Cl bond.

2) NaOH/ KOH - provide OH- ions.

3) as the OH- is a stronger nucleophile/ has a full negative charge (whereas water dipole)

State an explain whether the electronegativity of fluorine is greater than, same as or less than that of bromine.

Hence explain why HF can form H-bonds but HBr can't.

1) F more electronegative.

2) because it has less shielding.

3) so HF has a greater dipole moment/ is more polar than HBr.

Why is propane able to dissolve a large range of substances?

Because it has both polar and non-polar characteristics/ can form both London forces and H-bonds.

Thermal decomposition

The use of heat to break down a reactant into more than one product

Describe and explain the trend in thermal stability of group 2 carbonates down the group.

1) more thermally stable as you go down.

2) as the cations get bigger/ more shells.

3) so have less polarising effect/ distortion on the carbonate ion (anion)

Distillation:

What is the effect of the thermometer bulb being to high.

Incorrect boiling point reading/ product collected at wrong temp.

Carbon neutral fuel

A fuel that absorbs as much CO2 from the atmosphere (when it's produced) as it releases when it's burned.

Reasons why biofuels may not be carbon neutral.

1) energy required to manufacture fertilisers - to grow plants for good yield.

2) energy required to manufacture insecticides - to grown plants for good yield.

3) energy required to transport fuel to power plant.

2 effects that large scale production of biofuels may have on society.

CONS:

1) use of food crops to produce biofuels reduces food supply.

2) use of land for biofuels reduces biodiversity.

3) use of land to grow biofuels leads to reduced food supply.

4) use of land to grow biofuels leads to deforestation/leads to habitat loss.

PROS:

1) new jobs created to grow crops on new farmland.

2) less CO2 so less global warming.

3) less SO2 so less acid rain.

4) less SO2 so less respiratory illnesses e.g asthma.

Trend of hydroxides down group 2.

Solubility of hydroxides increases.

When chloroethane is heated with conc. ethanolic KOH what type of reaction occurs?

elimination.

when chloroethane reacts with aqueous KOH what type of reaction occurs?

substitution.

Use Maxwell-Boltzmann distributions to explain why gases react faster when the temperature is increased.

1) more molecules have energy greater than or equal to activation energy.

2) energy must be at least at activation energy for successful collision/ for reaction.

when chlorine is added to a solution containing bromide or iodide ions, a colour change occurs. What solvent would you add to the mixture to confirm the identity of the halogen produced?

hydrocarbon solvent/ named hydrocarbon solvent.

Give the result of the test of bromine in a hydrocarbon solvent.

brown.

Give the molecular formula of the organic product of the reaction between butanol and sodium.

C4H9ONa

Why is 2-chlorobutane more soluble in ethanol than in water? by considering the hydrogen bonding on the 2 solvents.

1) water has 2 hydrogen bonds per molecule whereas ethanol only has 1.

2) more energy required to break hydrogen bonds in water so it is less soluble/ H-bonding stronger in water.

secondary alcohol

An alcohol in which the -OH group is attached to a carbon atom that is attached to two other carbon atoms.