Alcohols And Haloalkanes Flashcards
Are alcohols polar or non-polar? Why?
Generally polar due to the electronegative hydroxyl group which pulls the electrons in the C-OH bond away from the carbon atom. The -OH group is also polar with a delta negative charge on the oxygen atom and a delta positive charge on the hydrogen atom
How does the size of an alcohol affect its solubility? Why?
As alcohols increase in size their solubility in water decreases.
When alcohols are mixed with water, hydrogen bonds are formed between the OH group and H2O.
If it’s a small alcohol hydrogen bonding let’s it mix freely with water.
In larger alcohols, most of the molecule is a non-polar chain, so there is less attraction for the polar H2O molecules.
What is the boiling point and volatility of alcohols like?
Relatively low volatility and relatively high BP compared to non-polar compounds of similar sizes because alcohols can form hydrogen bonds with each other &hydrogen bonding is the strongest type of intermolecular force.
What does a substitution reaction of an alcohol become? What catalyst is needed?
Alcohols react with compounds containing halide ions in a substitution reaction to become a haloalkane. Requires an acid catalyst such as H2SO4
What does an elimination reaction of an alcohol form? What catalyst is required?
Eliminating water from an alcohol forms an alkene. Can form an E/Z isomer as the OH group is removed but also an H, the H will be removed from a carbon adjacent to the carbon with the OH attached. Different isomers can form depending on which H is removed. (Pg248) Acid catalyst needed (concentrated H2SO4 or concentrated H3PO4. The mixture is then heated.
What oxidising agent is needed to mildly oxidise an alcohol?
Acidified potassium dichromate(VI). (K2Cr2O7/H2SO4)
What are primary alcohols oxidised to? What method is used to get the products?
Aldehydes and the carboxylic acids. Distillation to get aldehyde, reflux to get carboxylic acid
What are secondary alcohols oxidised to? What method is used?
Ketones. Using reflux
What is the colour change when oxidising an alcohol with acidified potassium dichromate?
Orange dichromate(VI) ion, is reduced to the green chromium(III) ion
What is the functional group of an aldehyde and a ketone?
CnH2nO
What is the suffix of an aldehyde?
-al (e.g. propanal)
What is the suffix for a ketone?
-one (e.g. propanone)
What is the difference between an aldehyde and a ketone?
Aldehyde has =O on end of chain, ketone has =O in middle of chain
What is a haloalkane?
An alkane with at least 1 halogen atom in place of a hydrogen
Are haloalkanes polar?
Yes - halogens generally much more electronegative than carbon, so the carbon-halogen bond is polar
What mechanism do haloalkanes react in?
Nucleophilic substitution reactions
What are haloalkanes hydrolysed to make? How?
Alcohols:
1. Hydrolysis with aqueous alkali
2. Hydrolysis with water
What does the speed of haloalkanes being hydrolysed depend on? How can this be measured?
Bond enthalpy - weaker carbon-halogen bonds break more easily. Iodoalkanes have the weakest bonds so hydrolyse fastest, fluroalkanes have strongest bonds, so are slowest at hydrolysing.
Can be measured by adding silver nitrate solution and timing how quickly a precipitate forms and a cross disappears
How can you identify a haloalkane?
React sample with water, silver nitrate solution and ethanol. Colour if precipitate formed tells you which halogen is present. Yellow = iodoalkane, cream = bromoalkane, white = chloroalkane
What are features of chlorofluorocarbons?
Very stable, volatile, non-flammable, non toxic
What is the issue with CFCs?
Destroys ozone layer. Ozone molecules absorb a lot of ultraviolet radiation which can cause sunburn and skin cancer
What is the mechanism for ozone depletion?
CF2Cl2 + UV -> CF2Cl radical + Cl radical
Cl radical + O3 -> O2 + ClO radical
ClO radical + O -> O2 +Cl radical (regeneration of Cl radical)
Overall reaction: O3 + O2 -> 2O2 (Cl radical is catalyst)
Other than CFCs what also breaks down ozone?
NO radicals from nitrogen oxides
What are alternatives to CFCs
HCFCs & HFCs used for now
HCFCs still damage ozone but much less
HFCs don’t contain Cl so don’t damage ozone
Both HCFCs and HFCs are greenhouse gases
Some hydrocarbons used in fridges, most aerosols use pump spray systems or nitrogen as propellant, industrial fridges & freezers use ammonia
What is the greenhouse effect?
The absorption and re-emission of infrared radiation by greenhouse gases in the troposphere
What are the main greenhouse gases?
Water vapour, carbon dioxide, methane
How do greenhouse gases cause global warming?
The C=O, O-H and C-H bonds in these molecules absorb IR radiation which makes the bonds vibrate more, extra energy is passed on to other molecules in the air by collisions giving other molecules more kinetic energy and raising overall temperature.
What does the contribution of a greenhouse gas on the greenhouse effect depend on?
- How much IR radiation one molecule of the gas absorbs
- How much of that gas there is in the atmosphere
- How long the gas stays in the atmosphere for
What is global warming?
The warming if the planet due to increased concentrations of greenhouse gases in the troposphere, which enhance the greenhouse effect
What are the consequences of global warming?
- Warmer oceans will expand & ice sheets could melt causing sea levels to rise and more flooding
- Stormier less predictable weather
- Less rainfall in some places leading to droughts & crop failures
- Increased rainfall in some places could bring diseases such as cholera
