CALCULATION OF THE EQUILIBRIUM CONSTANT OF INDICATOR

Purposes  Use the Spectrophotometer (T60U) and pH meter to measure 【 HIn 】, 【 In - 】 and 【 H + 】 in the solution, and calculate the equilibrium constant (Ka) of the equation.  Compare the result with the literature to calculate the deviation.  Observe the effect of the indicator through the titration.

Materials and Apparatus  Spectrophotometer (T60U)  pH meter  Phenolphthalein  bromthymol blue  methyl red  methyl orange  lacmus(litmus)  hydrochloric acid  sodium hydroxide

Procedures Prepare the solution of indicator Experiment One ： Use the Spectrophotometer (T60U) to measure 【 HIn 】 and 【 In- 】 Experiment Two ： Use pH meter to measure 【 H + 】 Compare experiment one and two, and calculate the Ka calculate the Ka of the equation Compare the result of the experiment and the Ka from literature to calculate the deviation and find the reason of the deviation. 為什麼並列

Acid-based Titration Figure out the color changing range of each indicator by Ka thymol blue fluoresceinlacmus methyl orange phenolphthalein Figure out the appropriate color changing range of the indicator Find out the deviation of the indicator in the inappropriate range during the titration conclusion

Step(One)-Preparation  Prepare the solution of the indicator ： mix the indicator with 20% of C 2 H 5 OH 、 0.1M NaOH solution 、 0.1M HNO 3.  Take seven volumetric flasks( 50ml ), formulate seven kinds of solutions ( from acid to basic ), and add NaOH into the 7 th volumetric flask which turns it into the form of “ In -.”  (Not finished?)

Step(Two)-Experiment 1  Set the Spectrophotometer’s wavelength at the range of 400nm~700nm, scan the sample in the acid (1 th volumetric flask )and the basic(7 th volumetric flask ) situation, and find the maximum wavelength( λ HIn 、 λ In- ).  Set the wavelength at λ HIn and measure the absorbance of all the samples.  Set the wavelength at λ In - and measure the absorbance of all the samples.  Calculate its equilibrium constant.

Step(One)-Experiment 2  Use pH meter to measure the pH value of all the samples and infer their 【 H + 】.  Calculate its equilibrium constant.