C2.7 Alcohols & Carboxylic Acids

What are carboxylic acids? Homologous series containing the functional group (often) written as –COOH or –CO2H Using R as the alkyl group, their structure is: They release H+ ions when added to water which makes them acidic. The pH of these solutions is between 3-6, showing that they are weak acids so that the equilibrium below lies mainly on the non ionised side (left hand side) RCOOH ⇋ RCOO- + H+

Reactions of carboxylic Acids – As An Acid General equations: Carboxylic acid + Base  Salt + Water Carboxylic acid + Carbonate  Salt + carbon dioxide + water Carboxylic acid + Hydrogen Carbonate  Salt + carbon dioxide + water Both soluble bases and solid bases neutralise carboxylic acids Both reactions would show a change in pH The carbonate reactions could be tested by adding limewater (turns milky with CO2) You need to be able to write word and symbol equations for each of these reaction along with state symbols!

Reactions of carboxylic Acids – As An Acid General equations: Carboxylic acid + Base  Salt + Water Carboxylic acid + Carbonate  Salt + carbon dioxide + water Carboxylic acid + Hydrogen Carbonate  Salt + carbon dioxide + water Word equation examples: e.g. Ethanoic acid + Sodium hydroxide  Sodium ethanoate + water e.g. Propanoic acid + Calcium carbonate  Calcium ethanoate + carbon dioxide + water e.g. Methanoic acid + Copper oxide  Copper methanoate + water e.g. Propanoic acid + Zinc carbonate  Zinc propanoate + water

Reactions of carboxylic Acids – As An Acid General equations: Carboxylic acid + Base  Salt + Water Carboxylic acid + Carbonate  Salt + carbon dioxide + water Carboxylic acid + Hydrogen Carbonate  Salt + carbon dioxide + water Symbol equation examples: e.g. Ethanoic acid + Sodium hydroxide  Sodium ethanoate + water CH3COOH(aq) + NaOH(aq)  CH3COONa(aq) + H2O(l) e.g. Propanoic acid + Calcium carbonate  Calcium ethanoate + carbon dioxide + water CH3CH2COOH(aq) + NaOH(aq)  CH3CH2COONa(aq) + CO2(g) + H2O(l) e.g. Methanoic acid + Copper oxide  Copper methanoate + water 2HCOOH(aq) + CaO(s)  (HCOO)2Ca(aq) + CO2(g) + H2O(l) e.g. Propanoic acid + Zinc carbonate  Zinc propanoate + water CH3CH2COOH(aq) + ZnCO3(aq)  (CH3CH2COO)2Zn(aq) + CO2(g) + H2O(l)

Knowledge Check 1. Write a word equation for the reaction between: Calcium carbonate (CaCO3) and Ethanoic acid Potassium hydrogen carbonate (KHCO3) and methanoic acid Propanoic acid and Sodium Hydroxide Pentanoic acid and Sodium Hydroxide 2. Write symbol equations for each of the above reactions including state symbols.

Knowledge Check 1. Calcium carbonate + Ethanoic acid  Calcium ethanoate + Carbon dioxide + Water Potassium hydrogen carbonate + methanoic acid  Potassium methanoate + Carbon dioxide + Water Propanoic acid and Sodium Hydroxide  Sodium Propanoate + water Pentanoic acid and Sodium Hydroxide  Sodium Pentanoate + Water 2. CaCO3(s) + 2CH3COOH(aq)  (CH3COO)2Ca(aq) + CO2(g) + H2O(l) KHCO3(aq) + HCOOH(aq)  HCOOK(aq) + CO2(g) + H2O(l) CH3CH2COOH(aq) + NaOH(aq)  CH3CH2COONa(aq) + H2O(l) CH3CH2CH2CH2COOH(aq) + NaOH(aq)  CH3CH2CH2CH2COONa(aq) + H2O(l)

Reactions of carboxylic Acids – Esterification General equations: Carboxylic acid + alcohol ⇋ Ester + Water Conditions: Heat and concentrated sulfuric acid catalyst You need to be able to write word, symbol and displayed equations for this reaction. e.g. Ethanoic acid + Ethanol  Ethyl ethanoate + Water CH3COOH + C2H5OH ⇋ CH3COOC2H5 + H2O Worked examples: Ethanoic acid + Methanol Propanoic acid + Ethanol

Reactions of carboxylic Acids – Esterificaton

Reactions of carboxylic Acids – Esterificaton The ester can be separated from the reaction mixture by distillation because it will have a different boiling point.

Knowledge check Write an equation to show the reaction that occurs when 2-chloro-3-methylbutanoic acid, CH3CH(CH3)CHClCOOH, reacts with butan-2-ol. Concentrated sulphuric acid is added to the reaction mixture. What is the purpose of the sulphuric acid? Why can the ester be distilled off, leaving the other organic substances in the reaction flask?

Answers a) b) Sulfuric acid acts as a catalyst 2. The ester has the lowest boiling point. Alcohols, carboxylic acids and water all contain the –OH group and can hydrogen bond. This increases their boiling point. Esters cannot hydrogen bond.