Acid / base titration

background [prelab assignment (10 points) due at the beginning of the lab]

define "equivalence point" 

define "end point"

• include & define "pH indicator" in your response
• relate to equivalence point

• 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

compare the determination of [HCl] using

• the equivalence point by finding the inflection point using either DataStudio or Excel
• the end point   [record buret volume at color change]

materials

buret; ring stand with buret holder

beaker, pH meter, bromothymol blue

solid NaOH, water, balance, graduated cylinder

aqueous solution of HCl [unknown concentration]

methods [delegate lab work]

prepare 0.4 M NaOH solution

rinse buret with water, then NaOH solution prior to use

use the above solution to determine the unknown [HCl] solution (~30 mL)

use / calibration of probe device  [see vodcast; iPod download available]

1. turn-on Xplorer data collection device
2. insert pH probe into pH transducer, which is inserted into the Xplorer 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
12. DO NOT PRESS ANY OTHER BUTTON DURING YOUR MEASUREMENT
13. 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 [15 points; no lab report revision]

data analysis

titration curve & corresponding plot of its first derivative

determination of [HCl] based on the end point and equivalence point

statistical analysis  & conclusion

resource

example of titration protocol

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

video:  effect of acid on biological tissue (demo);  rinsing a buret  [access 1 / 2010]