Download Neutralization of acid and base

Neutralization Titration Package (SCS-200)
pH Neutralization Titration experiment
We feel itching when we are bitten by insects. When insects bite human, the acidic substances are injected to human
body. We can release the swallow by applying human spits or ammonia solution that are basic in property since they
neutralize with acidic substances from the insects. Let's find out about what neutralization is and how pH changes
occurs with ScieceCube’s Neutralization Titration Package.
1. Lab materials
Content
Product no.
Pcs
Specification
pH sensor
KDS-1005
1
pH 0 ~ 14
ScienceCube Pro
KDM-1002
1
Temperature sensor
KDS-1001
1
-25℃ ~ +125℃
Micro Stirrer
KDA-23
1
67 * 67 * 27mm
4
Hydrochloric acid, Acetic acid,
Reagent
Sodium hydroxide, Ammonia water
Indicator
3
BTB, Methyl orange,
Phenolphthalein
Micro stirrer Magnet
NTS-100
4
Sample Bottle
12
Stand
1
Stand Clamp
1
Beaker
1
50ml
Burette
1
70ml
2. Theory to Explore
1) Neutralization is also called as an acid-base reaction. It is a reaction in which acidic hydrogen ion(H+) meets basic
hydroxyl ion(OH-) and becomes water. We can observe the change in pH during the reaction.
HCL + NaOH-NaCl + H2O
2) Neutralization is usually completed with strong acid and base. In other cases, neutralization is not always guaranteed.
3) Quantitative analysis can be performed by neutralization from being proper with acid and base of unknown
concentration. Neutralization is fast in progress among chemical reactions. Generally, we can even use the way of
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observing the color change of test solution if strong acid and base are used. In other case, deciding of neutralization
point can be difficult since change in pH is too small even with using the test solution. We can easily obtain the proper
value of the neutralization however by MBL experiment. So forth, the process of finding out of the concentration of
acid or base of unknown concentration is called, neutralization titration.
[H3O+]
=(initial HCl mole concentration * intial HCl volume - NaOH volume * initial NaOH mole concentration)/(initial HCl
volume + NaOH volume)[OH-]
=(NaOH volume * initial NaOH mole concentration-initial HCl mole concentration * initial HCl volume)/(initial HCl
volume + NaOH volume)
3. Things to Consider
1) Avoid acidic and basic solution from contacting with human body and wear safety goggles and gloves during
experiment.
2) Be careful with glassware such as beaker since it can break and cause wounds.
3) Do the [zero-setting] of pH sensor by measuring of pH repeatedly in buffer solution pH 4.0, 7.0, and 10.0.(use
distilled water for washing the sensor)
4) Before using burette, wash it twice by sodium hydroxide solution.
5) The electrodes can be damaged if experimented for a long period with strong acidic or basic solution of more than
1.0M. Always keep the instruction manual of the pH sensor in mind.
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Notes !
Followings are explanations on safekeeping, zero-setting and using manual of pH sensor made of standard compound
electrodes(standard compare pole and glass pole Ag/AgCl).
1. When pH sensor is not used, reserve the compound electrodes (glass) by soaking in 3.3M KCl container provided after
washing them throughly with distilled water (dry with filter paper). For a short period, reservation of compound electrodes is
possible with standard buffer solution of pH 4.0 or 7.0. However, for a long period, they must be kept in pH 4.0 3.3M KCl solution.
2. Take out the pH sensor reserved in KCl container. Wash the electrode with distilled water and absorb moisture with filter
paper (Be careful not to wipe the glass pole).
3. Soak the poles in pH 7.0 standard solution and carry out [zero-setting] in science experiment menu [Design of experiment] in
Excel.
4. After completing [02], wash the pole with distilled water. Then dry water with filter pater and soak the pole in pH 4.0
standard solution. After that, start the [zero-setting]. Take out the pH pole from pH 4.0 standard solution then wash it again with
distilled water. Start [zero-setting] with pH 7.0 standard solution. [zero-setting] can be set with pH 10.0 standard solution when
using with basic solution.
5. Perform the calibration precisely by repeating the procedure [02] and [03].
6. After washing the pH pole with distilled water, measure the pH by soaking it in experimental reagent.
7. Setting can be reserved in interface once standard [zero-setting] is set. However, it can change back to original if interface
or sensor is disconnected from the computer.
8. In case of pH value that is measured in 3.3M KCl reserving solution changes greatly, reaction is slow, and measurement of
pH from standard solution comes out in error, disuse the pole and replace with new one.
[PICTURE
1] Washing pH pole
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4. Procedure
-pH Neutralization reaction
1) Prepare a computer, MBL interface and pH sensor and carry out [zero-setting] of pH sensor in science experiment
menu [Design of experiment] in Excel.
2) Put hydrochloric acid 4cc in a beaker by using the burette.
3) Let BTB indicator two drops in to 2).
4) Put small magnet in the beaker, and turn on the micro stirrer.
5)Drop sodium hydroxide one drop by one till the color changed completely. Let’s investigate the pH level and
temperature change with ScienceCube pH sensor and temperature sensor.
6) Analyze the relationship between the sodium hydroxide quantity and the pH level, temperature with ScienceCube
software.
7) Try above procedure with other kinds of reagent and indicator.
Tips
Burett
Always
perform
[zero-
setting]
of
sensor
before
use.
throughly
pH Sensor
water
pH
Wash
with
whenever
changing the materials.
Beaker
Amplifier
Micro
Sitrrer
[FIGURE 1] Experiment of neutralization reaction of acid and base
[PICTURE 2] Experiment of pH neutralization reaction
4
it
distilled
5. Result
-pH Neutralization reaction
Experimental design and analysis
Calculation formula of data and Excel
room temperature
23C
reagent
Phenolphthalein 5drops
NaOH speed of volume change (mL/s)
0.23
HCl mole concentration
0.1
HCl volume (mL)
30
NaOH mole concentration
0.1
NaOH volume (mL)
30(put 35mL in burette)
1 NaOH Volume(mL)
=+B4*$N$6
2 Δ (pH/ NaOH Volume)
=+(C5-C4)/(F5-F4)
3 H3O+
=+($M$8*$M$9-F4*$M$10)/($M$9+F4)
4 OH-
=+(F4*$M$10-$M$8*$M$9)/($M$9+F4)
<TABLE 1> Variable design of experiment of pH neutralization reaction
Tips
Prepare auto-calculation
formula as in <TABLE 111>
for
NaOH,
(3)[H3O+]
(1)volume
of
(2)^pH/NaOH,
ion,
(4)[OH-
]concentration of ion on
worksheet in Excel. Then,
[FIGURE 11-1] Experiment of neutralization reaction of acid and base
copy up to the data
series range with filling
handle.
[FIGURE 2] Results of experiment of pH Neutralization reaction
Notes !
Convert the rate of volume change of NaOH according to time as in [FIGURE 11-2].
Average rate of volume change of NaOH dropping from burette for 50 seconds is 6.5.L/50s=0.13mL/s. Multiply this value by
value of B series($J$6) which is the time data series and make a calculation formula(=+B4*$J$6) in F4 series. Then, copy it to
F series with filling handle. By doing this, volume of NaOH is calculated automatically according to time in Excel. Although
we actually measured the time and change of pH in experiment, draw the X-Y graph(volume F series in X-axis, pH C series in
Y-axis) by chart wizard after modifying the rate of change according to time to the rate of volume change. Also, measure
the rate of volume change of NaOH dropping from burette precisely with electronic scale.
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[FIGURE 3] Analysis of pH neutralization reaction 1
[FIGURE 4] Analysis of pH neutralization reaction 2
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6. Discussion
1) Explain the change of pH according to time. How can we obtain the graph of relationship of pH and volume?
2) Explain how the change of pH in relation to time is different from the change of pH in relation to volume.
3) Draw the neutralization reaction curve using various detergent in surroundings. Predict the shape of the graph and
compare with the actual result.
7. Investigation
-Principle of measuring of pH
Electrochemically, change of voltage that occurs in pH pole has a linear relationship with change of pH of solution.
change of voltage in pH pole is measured by calibration with slope and intercept.
Change of voltage in pH electrodes working with very small amount of current appears by mV level. To carry out the
precise measurement, the pH sensor should be shielded in order to cut it off from the electric effects by relatively large
voltage in our surroundings.
If we use automated neutralization experiment and program we can perform the experiment by controlling
concentration of NaOH precisely.
By the theory of Nernst, when gas constant(R), absolute temperature(T) and Faraday constant(F) relationship between
voltage of solution and [H+] is indicated as
E = E0 −
RT
1n[ H + ] …①
F
Thus, voltage in solution is linear in properties with change of pH. To obtain the relative formula of line from ①, we
need standard buff solution of known pH value in fixed temperature. Basically, we can perform the calibration with one
pH 7.0 standard solution for all pH range. However, for more precise experiment, other standard solution such as pH
4.0 or pH 10.0 is needed.
It is important that we stir the solution regularly with a stir station to measure pH more precisely. The calculation
formula for pH neutralization point is shown as next.
Since [H+] of n1 mole and [OH-] of n2 mole are equal, relationship of volume of mole concentration and mole numbers
are as next.
n1 M 1V1 = n2 M 2V2 …②
We can explore on relationship between [H+] and [OH-] in relation to change of volume of NaOH solution, once we put
down the equation ② in worksheet in Excel.
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Rev. 24/8/2007
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