3.5 Alcohols Flashcards
What is the functional group of an alcohol ?
Hydroxide (OH-)
What is the general formula of an alcohol ?
CnH2n+1OH
What kind of intermolecular forces do alcohols have ?
•Van der waals
•Hydrogen bonds (OH)
How do alcohols mp and bp compare do other hydrocarbons ?
Higher, as alcohols have Hydrogen bonding whereas other molecules like alkanes do not
Are alcohols soluble in water ? Why does solubility depend on chain length ?
•Short chains are soluble as the OH has slight charges
•Long chains are insoluble as the non polar C-H take priority.
What makes an alcohol primary ?
When the carbon that contains the OH group is only bonded to one other carbon.
What makes an alcohol secondary ?
When the carbon containing the OH group is bonded to two other carbons.
What makes an alcohol tertiary ?
When the carbon containing the OH group is bonded to 3 other carbons.
How can ethanol be made from a product of crude oil fractionation ?
Hydration of ethene via electrophilic addition (H2PO4 catalyst).
What are the advantages and disadvantages of producing ethanol via hydration of ethene ?
Advantages - fast, continuous process with high yield purity
Disadvantages - non renewable as ethene is obtained from crude oil.
How can ethanol be made from fermentation ?
Plant carbohydrates are broken down and fermented by enzymes in yeast -> ethanol.
What conditions are needed for fermentation of plant carbohydrates to take place
•Enzymes in yeast as a catalyst
•35 degrees C
•anaerobic conditions.
Write an equation for the fermentation of glucose
C6H12O6 (aq) -> 2C2H5OH + 2CO2.
What are the advantages and disadvantages of obtaining ethanol from fermentation ?
Advantages - renewable
Disadvantages - slow, batch process, enzymes denature at low alcohol conc so is not pure and requires distilling.
Define carbon neutral
No net CO2 emissions into the atmosphere.
Explain why the combustion of ethanol as a fuel is described as neutral ?
As the CO2 released in fermentation and combustion is the same as what is taken in during photosynthesis.
Why, in actuality, is using fermented ethanol as a fuel not carbon neutral ?
As other costs, such as that of transport, affect neutrality.
What an equation for the combustion of ethanol.
C2H5OH + 3O2 -> 2CO2 + 3H2O
What is an elimination reaction ?
The removal of a smaller molecule from a larger one.
What group leaves the parent molecule in elimination reactions of alcohols ?
The OH and a H to form water
What physical conditions are needed for the elimination reactions of alcohols to alkenes ?
Excess hot concentrated sulphuric acid or pass over hot aluminium oxide.
Describe the mechanism for the dehydration of ethanol
Describe a method for dehydration of ethanol in a lab
Ethanol is heated with an excess of concentrated sulfuric acid at a temperature of 170°C, all in a boiling tube
What forms if you partially oxidise an alcohol ?
An aldehyde.
What conditions are needed to partially oxidise a primary alcohol ?
Dilute sulphuric acid, potassium dichromate, distill product as it is produced, gentle heating.
Write an equation for the partial oxidisation of ethanol
CH3CH2OH (l) + [O] -> CH3CHO (g) + H2O (l)
What is formed if you fully oxidise an alcohol ?
A carboxylic acid
What conditions are needed for the complete oxidation of an alcohol ?
Concentrated sulphuric acid, potassium dichromate, reflux for 20 mins, strong heating.
Write an equation for the full oxidation of ethanol.
CH3CH2OH + 2[O] -> CH3COOH + H2O
What forms if you oxidise a secondary alcohol ?
A ketone
Why can a ketone not be oxidised and why can tertiary alcohols not be oxidised ?
As a carbon-carbon bond would have to break and that requires too much energy
What conditions are needed for the oxidation of a secondary alcohol ?
Concentrated sulphuric acid, potassium dichromate, reflux for 20 mins, strong heating
Write an equation for the oxidation or propan-2-ol
CH3CHOHCH3 + [O] -> CH3COCH3 + H2O.
What is an aldehyde ? What is it’s functional group ?
A molecule with a C=O group at the end of a carbon chain.
What is a ketone ? What is it’s functional group ?
A molecule with a C=O group in the middle of a carbon chain.
What is a carboxylic acid ? What is it’s functional group ?
Molecule with a COOH group at the end of a carbon chain
Carboxyl group (COOH) consists of carbonyl (C=O) and hydroxyl (OH)
What does the Tollens test give a positive result for ?
Aldehydes
What molecule in Tollens Reagent reacts with aldehydes to give a positive result ?
Silver nitrate in NH3
This oxidises aldehydes but not ketones
Complex silver (I) ions reduced to Ag(s), forms a mirror.
How do you carry out the Tollens test ?
Add equal volumes of reactant and tollens solution to a test tube
Leave in water bath for 10 mins and observe changes.
What does the fehlings solution test for ?
Aldehydes
What is in Fehlings solution ? How does this react with the solution being tested ?
Copper (II) complex ions - a slight oxidising agent
The Cu2+ is reduced to Cu+ (brick red)
What conditions do you need to do the Fehlings solution test
Heat
What result do aldehydes and ketones give the Fehlings test
Aldehydes - brick red ppt forms
Ketone - no reaction.
