Page 11 - Physical chemistry understanding our chemical world

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6.4 pH buffers 267
Why does the pH of blood not alter after eating pickle? 267
Why are some lakes more acidic than others? 267
How do we make a ‘constant-pH solution’? 270
6.5 Acid–base indicators 273
What is ‘the litmus test’? 273
Why do some hydrangea bushes look red and others blue? 274
Why does phenolphthalein indicator not turn red until pH 8.2? 276

7 Electrochemistry 279
7.1 Introduction to cells: terminology and background 279
Why does putting aluminium foil in the mouth cause pain? 279
Why does an electric cattle prod cause pain? 281
What is the simplest way to clean a tarnished silver spoon? 282
How does ‘electrolysis’ stop hair growth? 283
Why power a car with a heavy-duty battery yet use a small battery in a
watch? 283
How is coloured (‘anodized’) aluminium produced? 285
How do we prevent the corrosion of an oil rig? 286
What is a battery? 288
Why do hydrogen fuel cells sometimes ‘dry up’? 289
Why bother to draw cells? 291
Why do digital watches lose time in the winter? 293
Why is a battery’s potential not constant? 294
What is a ‘standard cell’? 295
Why aren’t electrodes made from wood? 300
Why is electricity more dangerous in wet weather? 302
7.2 Introducing half-cells and electrode potentials 303
Why are the voltages of watch and car batteries different? 303
How do ‘electrochromic’ car mirrors work? 305
Why does a potential form at an electrode? 306
7.3 Activity 308
Why does the smell of brandy decrease after dissolving table salt in it? 308
Why does the smell of gravy become less intense after adding salt to it? 308
Why add alcohol to eau de Cologne? 309
Why does the cell emf alter after adding LiCl? 312
Why does adding NaCl to a cell alter the emf, but adding tonic water
doesn’t? 314
Why does MgCl cause a greater decrease in perceived concentration than
2
KCl? 315
Why is calcium better than table salt at stopping soap lathering? 316
Why does the solubility of AgCl change after adding MgSO ? 318
4
7.4 Half-cells and the Nernst equation 321
Why does sodium react with water yet copper doesn’t? 321