(b) Liquids and solutions

• Method and uses of linear and log dilution

  • Dilutions in a linear dilution series differ by an equal interval, for example 0·1, 0·2, 0·3 and so on.

  • Dilutions in a log dilution series differ by a constant proportion, for example 10-1, 10-2, 10-3 and so on.

• Production of a standard curve to determine an unknown

  • Plotting measured values for known concentrations to produce a line or curve allows the concentration of an unknown to be determined from the standard curve.

• Use of buffers to control pH

  • Addition of acid or alkali has very small effects on the pH of a buffer, allowing the pH of a reaction mixture to be kept constant.

• Method and uses of a colorimeter to quantify concentration and turbidity

  • Calibration with appropriate blank as a baseline; use of absorbance to determine concentration of a coloured solution using suitable wavelength filters; use of percentage transmission to determine turbidity, such as cells in suspension.