alcohols Flashcards
What is the general formula for alcohols?
C_nH_(2n+1)OH
Hydroxy suffix is used if the prefix cannot be applied.
What allows the -OH group in alcohols to form hydrogen bonds with water?
The -OH group is polar due to the electronegativity of oxygen
The oxygen is delta negative, and the hydrogens in water are delta positive.
Why are short chain alcohols soluble in water?
Hydrogen bonding predominates over van der Waals forces
The hydrocarbon chain is non-polar.
What happens to the solubility of alcohols in water as the chain length increases?
Solubility decreases
The non-polar hydrocarbon chain dominates.
How do the boiling points of alcohols compare to alkanes of similar molecular mass?
Alcohols have higher boiling points due to hydrogen bonding
The -OH group can hydrogen bond to other alcohol molecules.
What is the bond angle of the C-O-H bond in alcohols?
104.5 degrees
This angle is reduced due to lone pair repulsion.
What is the most important alcohol and its formula?
Ethanol, C2H5OH
Used as a solvent and can be made from crops.
What are the two main methods for producing ethanol?
- Fermentation
- Hydration of ethene
What is the primary raw material for fermentation?
Glucose from plants
Plants photosynthesize to produce glucose.
What is the temperature condition for fermentation?
Approximately 35°C
This temperature is a compromise to prevent enzyme denaturation.
What are the advantages of fermentation for ethanol production?
- Cheap
- Uses low tech equipment
- Renewable resources
What is a disadvantage of fermentation?
It is a batch process that is slow and costly
Produces impure ethanol requiring fractional distillation.
What is the overall equation for fermentation and combustion of ethanol?
C6H12O6 + 6O2 → 6CO2 + 6H2O
This illustrates carbon neutrality, although not entirely accurate due to fossil fuel use.
What is the temperature and pressure required for the hydration of ethene?
250-300°C and 70 atmospheres
High pressure is necessary to break the double bond.
What is the main disadvantage of the hydration of ethene?
It relies on non-renewable crude oil
This can lead to increased costs as resources diminish.
What are the three types of oxidation reactions for alcohols?
- Primary alcohol → aldehyde → carboxylic acid
- Secondary alcohol → ketone
- Tertiary alcohol → cannot be oxidized
What is the reagent used for the oxidation of primary alcohols?
Potassium dichromate (K2Cr2O7) and dilute sulfuric acid
This oxidizing agent is crucial for the reaction.
What observation indicates the oxidation of a primary alcohol?
Orange Cr+6 ions are reduced to green Cr+3 ions
This indicates the alcohol has been oxidized.
What distinguishes aldehydes from ketones in oxidation reactions?
Aldehydes can be further oxidized to carboxylic acids, ketones cannot
This is the basis for distinguishing tests.
What reagent is used in the Tollens’ test for aldehydes?
Tollens’ reagent, formed by mixing aqueous ammonia and silver nitrate
The active species is the [Ag(NH3)2]+ complex ion.
What is the observation when aldehydes react with Tollens’ reagent?
A silver mirror forms in the test tube
Ketones do not cause any visible change.
What happens in Fehling’s solution when an aldehyde is present?
Blue Cu2+ ions change to a red-orange precipitate of Cu2O
Ketones do not react with Fehling’s solution.
What is the product of the dehydration of alcohols?
Alkene
This reaction requires concentrated sulfuric or phosphoric acids.
