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3.1.4 the pH scale

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chem whatarethemechanismsofchemicalchange

Reactivity 3.1.4 - the pH scale can be used to describe the of a solution

since the majority of acids encountered are weak, the hydrogen ion concentration expressed directly as produces numbers with large negative exponents

taking the logarithm of the concentration of hydrogen ions makes expressing the concentration of an acid more user-friendly

the scale is theoretically infinite and can extend into negative numbers, but common acids and bases will have positive values and fall within the range of

this corresponds to in the range to

a change of 1 represents a 10-fold change in

measuring pH

  • universal indicator
    gives a colour that can be compared with a colour chart. narrower-range indicators are more accurate. the interpretation of the colour of an indicator is always subjective, so they are useful for estimations and comparisons rather than for precision.

  • pH meter
    pH meters are more objective and usually more accurate method, reading the directly.

must be calibrated and standardised for the temperature

challenge questions
  1. derive equations to show why aluminium sulfate, when added to water, gives a cloudy appearance and has a low pH.
  1. suggest why some gardeners water hydrangea flowers with a weak solution of vinegar

vinegar is a weak acid, so to turn hydrangea flowers blue

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