• Determination of iron in a razor blade
• Determination of acetic acid in vinegar
• Determination of Alcohol in Blood
Must do three things before You start
• 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
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
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)
What I would like . . .
• In this experiment you will determine the
amount of acid needed by titration with the
strong base NaOH.
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,
Excellent to use!!!
Can actually obtain 1 mole of H+
by using a balance
• 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
• 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
Commonly used equipment
• Erlenmeyer Flask
• Magnetic Stir Plate
• Electronic Balance
• 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.
• 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.
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.
Goto pdf. . . .
XXXX g sample -> g KHP -> mol KHP ->
mol NaOH -> M NaOH
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
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
The net ionic equation
H + (aq) + H2O(l) <-> H3O + (aq)
• Pure water already contains small quantities
of the H + ion (proton), H3O + (hydronium ion)
• 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 g KHP
• Note that 1 equiv = 1 mol for both KHP and NaOH
so N = M and molecular weight = equivalent
• 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 g KHP mol KHP mol
NaOH M NaOH
• 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.