WEBVTT 00:00:00.500 --> 00:00:03.976 Welcome to GCSE Edexcel Science revision. 00:00:04.126 --> 00:00:08.160 Unit S C 23: Alcohols and carboxylic acids. 00:00:10.833 --> 00:00:16.251 Alcohols contain the O H functional group attached to carbon, called a hydroxyl group. 00:00:16.401 --> 00:00:21.841 A functional group is the part of a molecule responsible for its characteristic reactions. 00:00:21.991 --> 00:00:29.286 The alcohol’s covalently bonded O H is different from a free hydroxide ion, O H, charge minus, in an alkali. 00:00:31.967 --> 00:00:47.090 The first four straight-chain primary alcohols here are methanol C H 3 O H, ethanol C H 3 C H 2 O H, propan-1-ol C H 3 C H 2 C H 2 O H and butan-1-ol C H 3 C H 2 C H 2 C H 2 O H. 00:00:47.240 --> 00:00:50.683 Show all atoms and bonds when asked for displayed formulae. 00:00:50.833 --> 00:00:55.698 The O to H group is bonded to the final carbon; all covalent bonds are shown. 00:01:00.367 --> 00:01:08.151 These members belong to a homologous series: they share the O H group, have similar reactions and differ successively by C H 2. 00:01:08.301 --> 00:01:11.264 Their boiling points generally rise with chain length. 00:01:13.933 --> 00:01:16.024 Alcohols burn in oxygen. 00:01:16.174 --> 00:01:26.413 Complete combustion produces carbon dioxide and water; ethanol obeys C 2 H 5 O H plus 3 O 2 produces 2 C O 2 plus 3 H 2 O. 00:01:26.563 --> 00:01:30.573 Insufficient oxygen can produce carbon monoxide or soot. 00:01:33.233 --> 00:01:37.337 Alcohols can be dehydrated to form alkenes by removing water. 00:01:37.487 --> 00:01:43.384 Ethanol forms ethene: C 2 H 5 O H produces C 2 H 4 plus H 2 O. 00:01:43.534 --> 00:01:48.983 Dehydration is removal of the elements of water, not simply evaporation of solvent. 00:01:49.133 --> 00:01:53.219 The carbon count is unchanged; an alkene double bond forms. 00:01:57.900 --> 00:02:00.821 Ethanol can be oxidised to ethanoic acid. 00:02:00.971 --> 00:02:11.221 Other suitable primary alcohols can similarly form the carboxylic acid with the same carbon count; the required oxidising reagents are beyond the recall scope here. 00:02:13.900 --> 00:02:17.062 Methanol is toxic, and alcohols are flammable. 00:02:17.212 --> 00:02:22.064 Do not infer that every alcohol has the uses or safety profile of ethanol. 00:02:24.733 --> 00:02:31.858 Compare ethanol, propanol, butanol and pentanol by burning them in spirit burners beneath a known mass of water. 00:02:32.008 --> 00:02:37.457 Measure initial and final water temperatures and weigh each burner before and after heating. 00:02:37.607 --> 00:02:41.403 Keep the separation between flame and water container constant. 00:02:46.067 --> 00:02:52.759 Keep the water mass, burner-to-container distance, apparatus, starting temperature and mixing method consistent. 00:02:52.909 --> 00:02:58.487 Stir the water for a representative temperature and use a lid or draught shield where appropriate. 00:03:01.167 --> 00:03:06.690 Water energy gain equals mass times specific heat capacity times temperature rise. 00:03:06.840 --> 00:03:18.007 With water mass in grams and c equals 4.2 joules per gram per degree Celsius, the result is joules; energy per gram burned equals energy gained divided by fuel mass burned. 00:03:20.667 --> 00:03:29.283 For comparison per mole, calculate fuel moles from mass divided by relative formula mass, then divide measured energy by the amount burned. 00:03:29.433 --> 00:03:32.992 Per-gram and per-mole comparisons answer different questions. 00:03:35.667 --> 00:03:44.006 Heat loss to the surroundings and container, incomplete combustion, evaporation of fuel and changes in flame conditions reduce accuracy. 00:03:44.156 --> 00:03:48.419 A simple apparatus usually captures less than the true combustion energy. 00:03:51.100 --> 00:04:01.456 Use repeats and means, identify anomalies and avoid concluding that a larger temperature rise means a better fuel unless the amounts burned and conditions are comparable. 00:04:04.133 --> 00:04:11.929 Wear eye protection, keep spare fuel away from flames, extinguish burners safely with their caps and allow hot apparatus to cool. 00:04:12.079 --> 00:04:14.799 Never refill a burning or hot spirit burner. 00:04:17.467 --> 00:04:25.187 Carboxylic acids contain the C O O H functional group: a carbon with a C double bonded to O bond and an O H group. 00:04:25.337 --> 00:04:38.882 The first four are methanoic acid H C O O H, ethanoic acid C H 3 C O O H, propanoic acid C H 3 C H 2 C O O H and butanoic acid C H 3 C H 2 C H 2 C O O H. 00:04:39.032 --> 00:04:44.161 The carboxyl carbon has a C double bonded to O bond and a C to O, H group. 00:04:44.311 --> 00:04:46.167 It counts in the chain length. 00:04:50.833 --> 00:04:56.059 The carbon in the C O O H group counts towards the molecule’s total carbon number. 00:04:56.209 --> 00:05:02.768 Ethanoic acid has two carbons, while methanoic acid has one; do not omit the functional-group carbon. 00:05:05.433 --> 00:05:14.669 Solutions of carboxylic acids show acidic properties: they turn blue litmus red and react with suitable metals, bases, alkalis and carbonates. 00:05:14.819 --> 00:05:20.716 Many simple carboxylic acids are weak acids because only some molecules ionise in water. 00:05:23.367 --> 00:05:31.739 A carboxylic acid and an alkali form a salt and water; ethanoic acid with sodium hydroxide gives sodium ethanoate and water. 00:05:31.889 --> 00:05:34.885 The salt name changes the acid ending to -oate. 00:05:37.567 --> 00:05:42.554 With a carbonate, a carboxylic acid forms a salt, carbon dioxide and water. 00:05:42.704 --> 00:05:49.509 Confirm carbon dioxide by its ability to turn limewater cloudy; bubbles alone do not identify a gas. 00:05:52.167 --> 00:05:57.084 With a suitable reactive metal, a carboxylic acid forms a salt and hydrogen. 00:05:57.234 --> 00:06:02.471 Reaction rates depend on the acid and metal; do not claim all metals react equally. 00:06:05.133 --> 00:06:11.116 Members of the carboxylic-acid series have similar reactions because they share C O O H. 00:06:11.266 --> 00:06:14.781 Use the same pattern to predict a reaction of another member. 00:06:17.433 --> 00:06:20.355 That completes Alcohols and carboxylic acids. 00:06:20.505 --> 00:06:23.850 Revisit the notes and test yourself on the revision website.