Module 4: Section 2 Flashcards
What is the general formula of alcohols?
CnH2n+1OH
Why are alcohols soluble in water?
Alcohola are generally polar due to the highlyelectronegative oxygen atom. The hydrogen atom has a slight positive charge which can attract lone pairs on an oxygen from a neighbouring molcule, forming hydrogen bonds.
Why does solubility of alcohols decrease as size increases?
As alcohols get bigger, more of the molecule is a non-polar carbon chain.
Name the reaction for making a haloalkane from an alcohol.
Give the reagants and conditions.
Substitution reaction.
Requires an acid catalyst (H2SO4)
20 degrees celsius
Name the reaction for making an alkene from an alcohol.
Give the reagants and conditions.
Elimination reaction (Water is eliminated to dehydrate the alcohol)
Acid catalyst is required (H2SO4 or H3PO4).
Heat
What 2 products are made when you oxidise an alcohol by burning it?
CO2 and H2O
What is formed when you oxidise a primary alcohol by:
- Distillation
- Reflux
Distill = Aldehyde Reflux = Carboxylic Acid
What is formed when you oxidise a secondary alcohol?
Ketone
What is formed when you oxidise a tertiary alcohol?
Nothing. There is no reaction as tertiary alcohols dont react with K2Cr2O7/H+.
What colour change occurs when oxidising alcohols?
Orange —-> Green
Except for tertiary alcohols, which stay orange.
What reagants are used when oxidising alcohols?
K2Cr2O7 / H2SO4
What is a haloalkane?
An alkane with atleast 1 halogen atom in place of a hydrogen atom.
Why are haloalkanes more reactive than alkanes?
Halogens are more electronegative than carbon. The carbon-halogen bond is polar and so can be attacked by nucleophiles.
Name the reaction to form an alcohol from a haloalkane.
What are the reagants and conditions?
Nucleophilic substitution reaction.
Warm aqueous alkali (NaOH or KOH).
Reflux.
In a nucleophilic substitution reaction, name the way the bond breaks
Heterolytically. Both electrons from the C-X bond are taken by the X-
When water acts a nucleophile, what is the general equation for the nucleophilic substitution reaction?
R-X + H2O —> R-OH + H+ + X-
What does speed of hydrolysis depend on?
Bond enthalpy of the C-X bond.
What haloalkanes will hydrolyse the quickest and why?
Iodoalkanes will hydrolyse the fastest as they have the weakest bonds.
C-F is the strongest bond.
Give 4 properties of CFC’s
Stable, volatile, non-flammable and non-toxic.
What does Ozone in the upper atmosphere do?
It absorbs a lot of UV radiation and re-emits, reducing the amount of UV radiation that reaches the Earths surface.
Give 2 alternatives to using CFC’s
HCFC’s (hydrochloroflurocarbons)
HFC’s (hydroflurocarbons)
Describe the Greenhouse effect.
Gases in the atmosphere that contain C=O, C-H or O-H bonds are able to absorb IR radiation and re-emit it in all direction, including back down towards earth, keeping us warm.
What are the main greenhouse gases?
Water vapour, Carbon dioxide and methane.
