Page 10 - Physical chemistry understanding our chemical world

CONTENTS ix

5.5 Phase equilibria and colligative properties 212
Why does a mixed-melting-point determination work? 212
How did the Victorians make ice cream? 216
Why boil vegetables in salted water? 217
Why does the ice on a path melt when sprinkled with salt? 218
5.6 Phase equilibria involving vapour pressure 221
Why does petrol sometimes have a strong smell and sometimes not? 221
How do anaesthetics work? 222
How do carbon monoxide sensors work? 224
Why does green petrol smell different from leaded petrol? 224
Why do some brands of ‘green’ petrol smell different from others? 225
Why does a cup of hot coffee yield more steam than above a cup of
boiling water at the same temperature? 229
How are essential oils for aromatherapy extracted from plants? 229

6 Acids and Bases 233
6.1 Properties of Lowry–Brønsted acids and bases 233
Why does vinegar taste sour? 233
Why is it dangerous to allow water near an electrical appliance, if water is
an insulator? 235
Why is bottled water ‘neutral’? 236
What is ‘acid rain’? 237
Why does cutting an onion make us cry? 239
Why does splashing the hands with sodium hydroxide solution make them
feel ‘soapy’? 239
Why is aqueous ammonia alkaline? 240
Why is there no vinegar in crisps of salt and vinegar flavour? 241
How did soldiers avoid chlorine gas poisoning at the Second Battle of
Ypres? 242
How is sherbet made? 244
Why do steps made of limestone sometimes feel slippery? 244
Why is the acid in a car battery more corrosive than vinegar? 245
Why do equimolar solutions of sulphuric acid and nitric acid have
different pHs? 250
What is the pH of a ‘neutral’ solution? 251
What do we mean when we say blood plasma has a ‘pH of 7.4’? 251
6.2 ‘Strong’ and ‘weak’ acids and bases 253
Why is a nettle sting more painful than a burn from ethanoic acid? 253
Why is ‘carbolic acid’ not in fact an acid? 254
Why does carbonic acid behave as a mono-protic acid? 259
Why is an organic acid such as trichloroethanoic acid so strong? 260
6.3 Titration analyses 261
Why does a dock leaf bring relief after a nettle sting? 261
How do indigestion tablets work? 262