Carboxylic Acids and Alcohols

• Carboxylic acids are a homologous series of compounds containing the functional group '-COOH'.

Carboxylic Acids Formula and Naming

• The displayed formula for the '-COOH' group is -C(O)OH.
• The naming system mirrors alkanes and alkenes, using 'oic acid' as the suffix (e.g., methanoic acid, ethanoic acid, propanoic acid).
• Each molecule possesses the '-COOH' functional group, which can be situated at either end of the molecule.
• Displayed formulae can be converted into structural formulae.
• Vinegar constitutes an aqueous solution of ethanoic acid.

Alcohols

• Alcohols are a homologous series containing the '-OH' functional group, known as a hydroxyl group.
• Alcohols have the general formula CnH2n+1OH.
• The naming system aligns with alkanes and alkenes, using 'ol' as the suffix (e.g., methanol, ethanol).
• The position of the '-OH' group on the carbon chain is indicated by a number.
• The carbon chain is numbered to give the '-OH' group the lowest possible number.
• An exception to this rule involves methanol, as it only has one carbon atom; carbon number specification becomes unnecessary.
• For ethanol, the carbon atom with the '-OH' group is invariably carbon 1, eliminating the need to specify the carbon number.
• Displayed formulae can be converted into structural formulae.

Reactions of Alcohols

• Ethanol can undergo oxidation via complete combustion.
• In the presence of excess oxygen, complete combustion yields carbon dioxide and water represented by: C₂H₅OH (l) + 3O₂ (g) → 2CO₂ (g) + 3H₂O (l).

Ethanol Oxidation

• Ethanol can be oxidized in air by microorganisms (microbial oxidation), resulting in ethanoic acid and vinegar.
• This also occurs during fermentation as oxygen reacts with ethanol to form ethanoic acid.
• Heating ethanol with potassium dichromate(VI) (K₂Cr₂O₇) in sulfuric acid also oxidizes it to ethanoic acid represented by: CH₃CH₂OH + 2[O] → CH₃COOH + H₂O.
• The oxidising agent transitions from orange to green upon the conversion of the alcohol into a carboxylic acid.

Reactions of Carboxylic Acids

• Carboxylic acid solutions are weak acids with a pH around 5.

Chemical Test for Carboxylic Acids

• Add any carbonate to a suspected carboxylic acid sample. Carbon dioxide gas production, indicated by effervescence, confirms its identity.
• Carboxylic acids, react with carbonates to yield salt, water, and carbon dioxide (Metal carbonate + carboxylic acid → salt + water + carbon dioxide).
• Ethanoic acid forms an 'ethanoate' salt, and propanoic acid forms a 'propanoate' salt.
• Example Reaction: Reaction of zinc carbonate with ethanoic acid yields zinc ethanoate, water, and carbon dioxide.
• As weak acids, they react similarly to other acids, releasing H+ ions when reacting with a metal or base.

Ionic Formulae Production

• Determine the charge on the metal cation and non-metal anion.
• Check if the charges cancel: if they do, use a 1:1 formula, if they do not, calculate the cation-to-anion ratio.
• If more than one of an ion is needed, and that ion contains more than one element in its formula, use brackets.

Calcium Propanoate Example

• Calcium is located in Group 2, forming a 2+ cation, making propanoate a 1– anion.
• Two propanoate ions are necessary for each calcium ion, resulting in the formula Ca(CH₃CH₂COO)₂.
• Dilute carboxylic acids react with metals forming salt and hydrogen

Metal/Carbonate Observations

• Carbonates react away, producing CO₂ gas which causes fizzing. This reaction is slower than what is seen with strong acids like HCl.
• Metals react away, producing H₂ gas which also causes fizzing. Similar to reactions with carbonates, it's slower than reactions with strong acids like HCl.

Esters

• When a carboxylic acid reacts with an alcohol, it forms an ester. This is called a condensation reaction due to the production of a water molecule, which is also known as esterification
  • Reaction conditions: Heat and Concentrated H₂SO₄ (catalyst).
• Esters have the functional group '-COO-', with names split into two parts: alkyl -oate.
• Example Displayed Formula: Ethyl propanoate.
• The displayed formula can also be given as a structural formula.
• Reacting an ester with water alongside an acid catalyst reforms the original carboxylic acid and alcohol.
• Esters are volatile compounds, possess distinctive smells, and are used as food flavorings and in perfumes.

Condensation Polymerisation

• Condensation polymerization involves the reaction of a dicarboxylic acid with a diol, resulting in a polymer and water.
• A dicarboxylic acid has two '-COOH' functional groups, while a diol has two '-OH' functional groups.
• A polymer is a long chain containing many repeating units monomers.
• Dicarboxylic acid and diol are monomers that react together to form a condensation polymer through esterification.
• Each time monomers react, an H₂O molecule is released.
• This polymer type is classified as a polyester.
• With molecules containing millions of carbon atoms, repeat units can simplify things.

Polyester Repeat Units

• Polyesters feature repeating units of a dicarboxylic acid and diol.
• Trailing bonds and 'n' indicate the number of times the repeat unit repeats.
• Some polyesters, like biopolyesters, are biodegradable, meaning microorganisms in the environment can break down ester links naturally.

Manufacturing Ethanol

• Two Methods: Fermentation (renewable) and Hydration (non-renewable)

Fermentation Method

• Ethanol can be made from the fermentation of sugar using yeast, producing carbon dioxide as a waste gas in batches.
• Fermentation is anaerobic.
• If fermentation is carried out in the presence of air, the ethanol will oxidize via microbial oxidation, to form ethanoic acid.
• Temperatures of 30-40°C are optimal for enzymes.
  • Glucose ethanol + carbon dioxide: C6H12O6 -> 2C₂H₅OH + 2CO₂

Hydration Method

• Ethanol from ethene (crude oil product) heated at high pressure with steam and a catalyst, this is a continuous process that has no waste products
  • Ethene + water -> C₂H₄ + H₂O -> C₂H₅OH

Fermentation vs Hydration processes

• Fermentation: a batch process, inefficient, very slow, uses low temperatures and atmospheric pressure making it inexpensive and renewable material based on plant material.
• Hydration: a continuous process that is more efficient and very rapid. It uses high temperatures and pressures, so needing lots of energy input making it expensive, and uses finite resources based on crude oil.
• This is achieved Through fractional distillation: ethanol boils at 78°C, while water boils at 100°C.

Titration Method

• Steps:
  • Measure out 20cm³ of alkali into a conical flask using a pipette
  • Fill a burette to 50cm³ with the acid and put an indicator in the alkali
  • Add the acid drop-wise to the alkali until the indicator shows that the solution has become neutral.
  • Record how much acid was needed to neutralise the alkali.
• The titration is performed so we can measure the amount of one reactant (e.g. an acid) it takes to react with another reactant (e.g. an alkali) without excess of either one.
• The use of a burette makes the method reliable, this is the most accurate and precise piece of apparatus for measuring out volumes of liquids.
• 25cm³ is measured with a 25cm³ measuring flask. This is more accurate than a burette when measuring specific volumes.

Molar Volume

• Under standard conditions, one mole of any gas has a volume of 24dm³, also quoted as 24,000cm³ (dm³ * cm³ = multiply by 1,000)
• Standard conditions are when there is a temperature of 25 degrees C and a pressure of 1 atmosphere.
• Moles related to volume is: Moles = volume / 24, convert cm³ into dm³ by dividing cubic cm by 1000
  • To turn cm³ into dm³ divide by 1000

Solution Moles

• Moles = concentration (mol/dm³) x volume (dm³)