The bacterium Streptococcus pneumoniae is commonly found in the throat. S. pneumoniae produces hydrogen peroxide as it grows. A sample can be taken from a patient's throat and tested to measure the concentration of hydrogen peroxide. This can be used as a measure of the growth of the bacteria. You will determine the growth of bacteria by measuring the concentration of hydrogen peroxide in a solution that represents a sample taken from a patient. You will do this by measuring how long it takes for a sample of hydrogen peroxide to cause a colour change in a reaction mixture. The faster the mixture changes to a blue-black colour, the higher the concentration of hydrogen peroxide, and the greater the growth of bacteria. You will use a range of known concentrations of hydrogen peroxide to estimate the concentration of hydrogen peroxide in a sample. You are provided with the materials shown in Table 1.1. Table 1.1 labelled | contents | hazard | volume/cm³ ---|---|---|--- R1 | dilute sulfuric acid | irritant | 100 R2 | starch solution | low | 10 R3 | potassium iodide solution | low | 10 R4 | sodium thiosulfate solution | low | 10 H | 2.0% hydrogen peroxide solution | irritant | 25 U | solution representing patient sample | irritant | 10 W | distilled water | low | 100 If any solution comes into contact with your skin, wash off immediately with cold water. It is recommended that you wear suitable eye protection. You will need to carry out a serial dilution of the 2.0% hydrogen peroxide solution, H, to reduce the concentration by half between each successive dilution. You will need to prepare four concentrations of hydrogen peroxide solution in addition to the 2.0% hydrogen peroxide solution, H. After the serial dilution is completed, you will need to have 10cm³ of each concentration available to use.