determining concentration of chemical substances

• Serial dilutions are created by taking a series of dilutions of a stock solution. The concentration decreases by the same quantity between each test tube

  Serial dilutions are completed as a “standard” to compare against

  Comparisons can be:

  • Visual

  • Measured through a calibration/standard curve

  • Measured using a colorimeter

  
• A colorimeter is an instrument that beams a specific wavelength (colour) of light through a sample and measures how much of this light is absorbed.

  Colorimeters must be calibrated before taking measurements. This is completed by placing a blank into the colorimeter and taking a reference, it should read 0 (that is, no light is being absorbed)

  This step should be repeated periodically during a practical to make sure that the absorbance is still 0
• Using a colorimeter allows us to gain quantitative data which we can then plot on a calibration curve. This curve can then be used to find unknown concentrations.

  • Absorbance/transmission of light against the known concentrations is plotted

  • Unknown concentrations can then be determined from the graph