Acid / base titration

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

• sketch a data table for this lab containing entries for all required experimental measurements (i.e. review purpose & content of lab report)
• define "standardize" in the context of an acid or base
• pH indicator:  basis of its action ?  basis of its selection ?
• define:  end point & equivalence point
• msds information on HCl & NaOH
• review pH probe calibration video BEFORE lab (ipod download available, i.e. *.m4v file, which may be used during lab)
• review Excel tutorials screen casts (convert ; derivative) BEFORE day of lab data analysis 

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] 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 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 [30 points]

data analysis (25 points)

determine [HCl]

• titration curve& corresponding plot of its first derivative 
• based on the end point and equilivalence point

determine [NaOH]

• titration curves & corresponding plot of its first derivative
• based on the end point and equilivalence point

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

• compare [HCl] using end point versus equilivalence point
• compare [NaOH] using end point versus equilivalence point   

question  (5 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). 

resource

example of titration protocol

podcast of pH probe calibration

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