2. PURPOSE:
• To standardize a solution of sodium hydroxide
by titration with a primary standard,
potassium hydrogen phthalate (KHC8H4O4)

3. Use ph electrode

4. ANALYTICAL CHEMISTRY
• Determination of iron in a razor blade
• Determination of acetic acid in vinegar
• Determination of Alcohol in Blood

5. Must do three things before You start
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1. Clean the Buret
2. Delivering Solution from the Buret
3. Filing the Buret for a titration
4. Preparing the KHP Sample
5. Titrating the KHP
* Must use Your Lab book today!
*** This is one of the MOST complicated labs

6. KHP

7. Why use KHP?
• The hydrogen is slightly acidic, and it is often
used as a primary standard for acid-base
titrations because it is solid and air-stable,
making it easy to weigh accurately. It is not
hygroscopic. It is also used as a primary
standard for calibrating pH meters

8. as a buffering agent
• As a weak acid hydrogen phthalate reacts
reversibly with water to give hydronium (H3O+)
and phthalate ions.
HP- + H2O <->P2- + H3O+
• KHP can be used as a buffering agent(in
combination with hydrochloric acid (HCl) or
sodium hydroxide (NaOH) depending on which
side of pH 4.0 the buffer is to be)

9. What I would like . . .
• In this experiment you will determine the
amount of acid needed by titration with the
strong base NaOH.

10. What is a standardization???
• Since it is hard to prepare a NaOH solution of
accurately known concentration directly
from the solid, you will need to standardize
your NaOH solution against a precisely
weighed amount of standard acid.
• The acid used is the weak monoprotic acid,
potassium hydrogen.

11. Excellent to use!!!
Can actually obtain 1 mole of H+
by using a balance

12. A titration
• Knowing the volume of titrant added allows
the determination of the concentration of the
unknown. Often, an indicator is used to
usually signal the end of the reaction, the
endpoint

13. acid-base indicator
• An acid-base indicator is itself a weak acid (or
its conjugate base).
• An acid-base indicator is a weak acid having a
different colour in aqueous solution from its
conjugate base.

14. phenolphthalein

15. phenolphthalein
• Phenolphthalein
• Type: HIn + H2O <->In- + H3O+
pK: 9.5
Approximate pH range for color change:
• 8.0-9.8
Color of acid form: clear
Color of base form: red-violet

16. phenolphthalein

17. Commonly used equipment
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Buret
Erlenmeyer Flask
Magnetic Stir Plate
Electronic Balance

18. accuracy
• The accuracy of the results of your
titration will be a reflection of the
care you took while performing it.
When done carefully, titrations give
very accurate, precise results.
•

19. accuracy
• SOMETIMES!!!!!!!
• Titrations of unknown solutions are done in
two steps: a scout titration used to determine
the approximate amount of titrant needed
followed by the actual titration that you will
use to make your calculations.

20. What You will do . . .
• An 0.8167 gram sample of primary standard
KHP (assay = 99.95%) required 38.25 mL of
NaOH to neutralize.
Calculate the molarity of the NaOH solution.

21. Goto pdf. . . .
• Path:
XXXX g sample -> g KHP -> mol KHP ->
mol NaOH -> M NaOH

22. path
0.8167 g sample x (99.95g KHP)/(100 gram)
x (1molKHP)/(204.22g KHP)
x (1mol NaOH)/(1 mol KHP)
x (1 )/(0.03825 L)=
0.1040 M NaOH

23. Using the pH Probe

24. Using the pH Probe
• Using the pH Probe
• Preparation of the pH Sensor
• A pH sensor connected to a computer will be
used to measure pH. Plug the pH probe into
channel 1 of the interface box. Plug the power
cord on the interface box into an electrical
outlet.

25. Using the pH Probe

26. Best site
• http://www.chemistry.mtu.edu/~djchesne/cla
sses/ch2212/Tutorials/Vernier_pH_tutorial.ht
m

29. Arrhenius acids.

30. The net ionic equation
H + (aq) + H2O(l) <-> H3O + (aq)
• Pure water already contains small quantities
of the H + ion (proton), H3O + (hydronium ion)

31. On Exam
• Example: Calculate the weight of primary
standard potassium hydrogen phthalate
• (assay = 99.95%) that would be required to
standardize a 0.1 N NaOH solution,
• assuming a 40 mL titration.
• PATH: L NaOH 
mol NaOH 
mol KHP  KHP 
g
g sample
• Note that 1 equiv = 1 mol for both KHP and NaOH
so N = M and molecular weight = equivalent
weight.

32. • Example: An 0.8167 gram sample of primary
standard KHP (assay = 99.95%) required
• 38.25 mL of NaOH to neutralize. Calculate the
molarity of the NaOH solution.
• PATH: g sample  KHP 
g
mol KHP 
mol
NaOH  NaOH
M

33. • Example: A 1.7734 gram sample of KHP
required 40.11 mL of 0.1036 N for titration.
• Calculate the assay of the KHP and report with
a relative error of 1 part per 1000.