Lab 704, 2 students or 1 student

1
Exp 3. Hydrolysis of Salts and pH of Buffer
Solutions

• Lab 704, 2 students or 1 student

2

• Objective
• To learn about the concept of hydrolysis and to
  gain familiarity with
• pH meter and the behavior of buffer solutions

• Chemicals
• NaC2H3O23H2O, NaOH(6M), HCl(6M), HC2H3O2(3M)

NaCl
0.1 M
Na2CO3
0.1 M
NaC2H3O2
0.1 M
NH4Cl
0.1 M
0.1 M
ZnCl2
0.1 M
KAl(SO4)2
3
Use of pH meter

• To prepare the electrode to make pH measurements,
  follow this procedure.
• Remove the storage bottle from the electrode by
  first unscrewing the lid, then removing the
  bottle and lid. Thoroughly rinse the lower
  section of the probe, especially the region of
  the bulb, using distilled water.
• Connect the pH Sensor to the interface.
• Start the data-collect software. Press the power
  button.
• The software will identify the pH sensors and
  load a default data-collection setup. You are now
  ready to make pH measurements.
• Note Do not completely submerge the sensor. The
  handle is not waterproof.

4
Use of pH meter
-Rinse the electrode with distilled water and
place it in the sample to be measured. -Rinse the
electrode with distilled water again and try
another sample. Maintenance and storage -
Short-term storage (up to 24 hours) Place the
electrode in pH-4 or pH-7 buffer solution. -
Long-term storage (more than 24 hours) Store the
electrode in a buffer pH-4/KCl storage solution
in the storage bottle. ( When you are finished
making measurements, rinse the tip of the
electrode with distilled water. Slide the cap
onto the electrode body, then screw the cap onto
the storage bottle.)
5
Experimental

• Hydrolysis of Salts
• (Work in pairs, but evaluate your data
  individually.)

1. Boil 50mL of distilled water for 10 min to
expel dissolved CO2.
2. Prepare 50mL of 0.1 M NaCl, Na2C2H3O, NH4Cl,
ZnCl2, KAl(SO4)2, Na2CO3 solution, measure the pH
of these solutions and record the value.
NaCl
Na2C2H3O
NH4Cl
ZnCl2
KAl(SO4)2
Na2CO3
0.1 M
3. From the pH values that you determined,
calculate the hydrogen- and hydroxide-ion
concentrations for each solution. ?
Calculate the Ka or Kb
6

• pH of Buffer Solutions (Work this part
  individually)

1. Prepare Acetic acid-Sodium acetate Buffer.
Add 3.5g NaC2H3O23H2O 3 M Acetic acid 8.8 mL
Distilled water 55.6 mL
stirring
150mL beaker
2. Measure the pH of this solution by using a pH
meter.
7
3. Pour half (32 mL) of the buffer solution into
another beaker and label the two beakers 1 and 2.
1
Prepared buffer solution 1 (64.4ml)
2
8
4. Pipet 1mL of 6M HCl into beaker 1, mix and
then measure the pH of the resultant solution.
1
Measure the pH
mix
Add 1mL HCl (6M)
5. Pipet 1mL of 6M NaOH into beaker 2, mix and
then measure the pH of the resultant solution.
2
Add 1mL NaOH (6M)
mix
Measure the pH
9

• Summary

• Hydrolysis of Salts

1. Boil 50mL of distilled water for 10 min to
expel dissolved CO2. 2. Prepare 50mL of 0.1 M
NaCl, Na2C2H3O, NH4Cl, ZnCl2, KAl(SO4)2, Na2CO3
solution, measure the pH of these solutions and
record the value. 3. From the pH values that you
determined, calculate the hydrogen- and
hydroxide-ion concentrations for each solution ?
Calculate the Ka or Kb

• pH of Buffer Solutions

1. Prepare Acetic acid-Sodium Acetate Buffer and
measure the pH. (3.5g NaC2H3O2 -3H2O, 3 M
Acetic acid 8.8 ml, Distilled water 55.6 mL) 2.
Pour half of the buffer solution into another
beaker and label the two beakers 1 and 2. 3.
Pipet 1mL of 6M HCl into beaker 1, mix and then
measure the pH of the resultant solution. Pipet
1mL of 6M NaOH into beaker 2, mix and then
measure the pH of the resultant solution.
10
Using Hot Plates Safely
Hot plates offer convenience and important
safety benefits for use in preparing hot water
baths for mild to moderate heating. Use
only heat-resistant, borosilicate glassware, and
check for cracks before heating on a hot plate.
Do not place thick-walled glassware, such as
filter flasks, or soft-glass bottles and jars on
a hot plate. The hot plate surface should be
larger than the vessel being heated. Do not
use the hot plate in the presence of flammable or
combustible materials. Fire or explosion may
resultthe device contains components that may
ignite such material.
Stir control knob
Heat control knob
11
Place boiling stones in liquids being heated to
facilitate even heating and boiling. Do not
evaporate all of the solvent or otherwise heat a
mixture to dryness on a hot platethe glass may
crack unexpectedly when heated directly on a hot
plate. Use a medium to medium-high setting of
the hot plate to heat most liquids, including
water. Do not use the high setting to heat
low-boiling liquids. The hot plate surface can
reach a maximum temperature of 540 C. Do not
place metal foil or metal containers on the hot
platethe top can be damaged and a shock hazard
may result. Be careful when removing hot
glassware or pouring hot liquids from the hot
plate. Use tongs or silicone rubber heat
protectors (gripping devices). Turn off the
hot plate when not in use. The surface of a hot
plate stays hot for quite some timeand looks
exactly the same as a cold hot plate! Place a
bold, laminated HOT caution sign in front of
the hot plate immediately after use.
12
Balance Policies
Analytical balances, especially the four or five
place, digital or substitution balances, are
capable of measuring the weight of an object to
0.0001 or even 0.00001 grams-, -i.e. (0.1 mg or
0.01 mg). These balances if properly calibrated
and maintained are possibly the most
accurate and precise measuring instrument
found in any laboratory. Hence, it is
imperative that our shared analytical balances be
kept in excellent operating condition. I should
be noted that each balance is checked daily by a
member of the teaching staff for its proper
operation and general cleanliness. It is
absolutely imperative that each student needs to
first hear "Introductory Balance Talk" and do
the introductory about five minute weighing
experiment conducted by a qualified teaching
assistant. Then each student needs to adhere to
the rules that are given below.
13
General Rules for the Use of Analytical Balances
1. No one may use a balance without first hearing
an "introductory balance talk" given by a
teaching assistant. 2. Use only the balance to
which you are assigned. This must be done even if
the assigned balance is in use by another
assignee at this particular time. (Remember it
usually takes within 30 seconds. to accomplish
one weighing or only a matter of a few minutes to
complete a series of weighing). Posted
near the balance will be a list of those students
that have been assigned to use that particular
balance for the current semester. 3. If there
seems to be a problem with the balance, report it
immediately, to the instructor or
teaching assistant. Do not use another balance,
unless instructed to do so. 4. It is imperative
that you keep the balance and the immediate area
around the balance clean! Clean-up all chemical
spills and excess chemical after each use of the
balance. Do not leave old Kimwipes or crumpled
papers on the balance table. 5. When the
balances are not in use, the balance should be
always turned-off and in the case of the
substitution balances the beam arrested, all
weights on zero and the doors closed.
14
Please, clean the analytical balance an table
after use. Remember that chemicals and salt water
cause rapid and severe corrosion of
instruments.
15
Additional Usage Notes
16
Fast-Release Pipette Pump
Fit pipet up to 25mL Flexible elastic
thermoplastic rubber chuck holds pipet snugly for
safe, sure use. -Simply insert pipet into
detachable, cone-shaped chuck with light finger
pressure -To fill, grasp pump in palm of hand
and rotate knurled wheel with thumb -To empty
rapidly, lightly press thumb on quick-release
lever -To empty gradually, rotate wheel -Parts
disassemble for maintenance
17
Safety Wide Mouth Wash Bottle
Labeled Water with Blue Cap Use Distilled
Water ONLY.
Labeled Acetone with Red Cap Use Acetone ONLY.