Acid / base titration

 

background [prelab assignment (25 points) due at the beginning of the lab]

This laboratory activity is based on investigation 4 in your AP chemistry lab manual; thus, it provides some relevant background for the following prelab questions and this laboratory activity. While investigation 4 analyzes fruit juices, you will be analyzing an aqueous solution of a strong acid (HCl) and strong base (NaOH).

purpose

using a 0.5 M NaOH solution, standardize a HCl solution, then use the HCl solution to determine the concentration of an unknown NaOH solution

compare the determination of the unknown [NaOH] [HCl]using the equivalence point ( i.e. find the inflection point using your calculus background) versus end point (i.e. pH indicator color change)

materials

buret; ring stand with buret holder, 100 mL volumetric flask

beaker, pH meter, bromothymol blue

~ 0.5 M NaOH (prepared by YOU);  unknown [HCl] & [ NaOH]

2 aqueous solution of HCl & NaOH [unknown concentrations]

 

methods [delegate lab work]

rinse buret with solution (acid or base) prior to use

use the above solution to determine the concentration of the unknown [HCl] & [NaOH] solutions (~50 mL)

use / calibration of probe device - record the experimental protocol in your lab notebook, since you will use the pH probe in a subsequent lab

  1. insert pH probe into pH transducer, which is inserted into the Xplorer device
  2. turn-on Xplorer data collection device
  3. rinse pH electrode with water prior to entry into any solution - to prevent contamination between solutions
  4. press display button until the calibration screen appears
  5. press the check button
  6. press the tab button - to move among sign / digits
  7. press - or + button, as needed, to change sign / digits - to be adjusted to reflect pH of buffer
  8. put pH probe into buffer & swirl for at least 15 seconds [to ensure good contact between pH probe & buffer]
  9. press the check button
  10. repeat steps 6-9 for second buffer
  11. press display button; should see pH of solution
  12. press start / stop; wait ~ 10 seconds; press start / stop (to "save" calibration)
  13. press display button until the pH screen reappears
  14. DO NOT PRESS ANY OTHER BUTTON DURING YOUR MEASUREMENT
  15. the probe has being calibrated and is now ready for use; with about a minute of inactivity the probe will automatically power-down; simply turn it back on.

data analysis

student design

 

Content of lab report [35 points]

data analysis (15 points)

determine [HCl]

determine [NaOH]

statistical analysis (include interpretation of p-value) of class data  &  conclusion

questions  (20 points)

basis of selecting a pH indictator 

specify / justify a pH indicator you could use in this titration (except bromothymol blue) and an indicator that you should not use in this titration (hint: figure 16.4 in your textbook). 

error analysis - refers to postlab assesssment in investigation 4 in the AP chemistry lab manual

# 1, 2, 4

resource

example of titration protocol

lab activity source (examples):  site 1  & site 2 [access 4 / 2009]