Lab Report
Titration of Hydrochloric Acid with Sodium Hydroxide
Submit to
Dr. Patraphorn Sanguansat
By:
Apitta Kanchanapuping (Pao) 5961002
Nathapat Jaihow (Pooh) 5961039
Natwadee Nim-aussornkul (Dear) 5961078
Thunchanok Intachot (Earn) 5961100
Kannicha Eksuwancharoen (Dream) 5961101
Warit Ittisomboon (Heart) 5961123
Section 1107
General Chemistry
Mahidol University International Demonstration School
Semester 2 Academic year 2017 - 2018
Abstract
This lab report is about the experiment of the titration of Hydrochloric Acid (HCl)
with Sodium Hydroxide (NaOH). First, we draw HCl to the Erlenmeyer flask and add 2-3
drop of phenolphthalein. Second, we place the flask under the buret which contains NaOH
and open the stopcock to allow NaOH drop into the HCl flask. We add NaOH until the color
change to light pink and maintain for more than 30 seconds. After that, we did the same thing
two times. For the next part, we change the indicator from phenolphthalein to bromophenol
blue and follow same steps. However, we will look for gray when it starts to change color
instead of light pink. We record the data and calculate the unknown concentration of HCl. In
the end, the result that we get is: the concentration of HCl with the phenolphthalein indicator
is 0.0044 M and the concentration with bromophenol blue is 0.003567 M. Comparing both
results, the concentration with the phenolphthalein indicator is only very little higher.
Introduction
This lab report shows the result and the analysis of the experiment of the titration of
hydrochloric acid (HCl) with sodium hydroxide (NaOH). The purposes of the experiment are
to find the amount of NaOH that will affect the color of the solution once it reaches the end
point, to find the unknown concentration of HCl solution, and also to apply knowledge of
using glassware especially the buret and pipette.
Before doing this experiment, there are some background knowledges that we need to know:
1. Titration is a process of quantitative chemical analysis used to determine the unknown
concentration of an identified analyte. Since volume measurements play a key role in
titration, it is also known as volumetric analysis.
According to Helmenstine (2017):
A typical titration is set up with an Erlenmeyer flask or beaker containing a
precisely known volume of analyte (unknown concentration) and a color-change
indicator. A pipette or burette containing a known concentration of titrant is
placed above the flask or beaker of the analyte. The starting volume of the pipette
or burette is recorded. Titrant is dripped into the analyte and indicator solution
until the reaction between titrant and analyte is complete, causing a color change
(the endpoint). The final volume of the burette is recorded, so the total volume
used can be determined. (para. 2)
2. Hydrogen chloride (HCl) is a colorless gas at room temperature, which forms white
forms of hydrochloric acid upon contact with atmospheric water vapor.
3. Sodium hydroxide (NaOH) is a white ionic solid compound consisting of sodium
cations Na+ and hydroxide anions OH−. Sodium hydroxide is a highly caustic base
and alkali that decomposes proteins at ordinary ambient temperatures and may cause
severe chemical burns. It is highly soluble in water and readily absorbs moisture and
carbon dioxide from the air.
4. Bromophenol blue is used as a pH indicator, a color marker, and a dye. It can be
prepared by slowly adding excess bromine to a hot solution of phenolsulfonphthalein
in glacial acetic acid.
5. Phenolphthalein is a chemical compound with the formula C20H14O4 and is often
written as "HIn" or "phph" in shorthand notation. Phenolphthalein is often used as an
indicator of acid-base titrations. For this application, it turns colorless in acidic
solutions and pink in basic solutions. Phenolphthalein is slightly soluble in water and
usually is dissolved in alcohols for use in experiments. It is a weak acid, which can
lose H+ ions in solution. The phenolphthalein molecule is colorless, and the
phenolphthalein ion is pink. When a base is added to the phenolphthalein, the
molecule ⇌ ions equilibrium shifts to the right, leading to more ionization as H+ ions
are removed. This is predicted by Le Chatelier's principle.
6. The equation of how to convert molarity ⇔ mole
7. Acid and base color chart of indicator (phenolphthalein and bromophenol blue)
As stated by Wilson (2017):
Acid-base indicators are weak organic acids. Unlike most acids, however, the
acid and base forms of indicators are different colors. Since the color of the
indicator depends on the pH of the solution, indicators find wide use in
applications that involve pH changes, such as titrations, pH testing, and science
demonstrations.
The most important property of an indicator is its pH range, which is dependent
on the indicator's acid strength. An indicator's pH range is the range of pH
values over which the indicator changes colors from its acid form to its base
form. It extends from the highest pH at which only the acid form is visible to
the lowest pH at which only the base form is visible. The indicator is not
sensitive to pH changes outside its range because the indicator does not change
color over these pH values.
Experiment
1. Chemical/glassware
1) Beaker
2) Funnel
3) Buret
4) Volumetric Pipette
5) Erlenmeyer flask
6) Pipette gun
7) Distilled Water
8) Pipette
9) Sodium hydroxide (NaOH)
10) Hydrochloric acid (HCl)
11) Phenolphthalein (C12H14O4)
12) Bromophenol blue (C19H10Br4O5S)
13) Burette clamp
2. Procedures
Result
1. Prelab questions
1) How will you know when your titration is finished?
: When the color of the solution begin to change color and the new color persists for
at least 30 seconds, this means the solution reaches the endpoint. For phenolphthalein,
the color will change to light pink color and for bromophenol blue, it will change to
light gray color.
2) Label the pH scale below with acid, base, and neutral, indicating numbers for each.
3) On the scale above, use an arrow to show where your equivalence point is located.
: According to the chart, there is no equivalence point in the above indicator because
the end point of the indicator that we use isn’t pH 7; pH 9 for phenolphthalein and pH
4 for bromophenol blue. However, we suggest changing the indicator to bromthymol
blue or phenol red because their endpoint is the equivalence point (pH 7).
4) Write the neutralization reaction that occurs between hydrobromic acid (HBr) and
lithium hydroxide (LiOH).
: HBr + LiOH => H2O + LiBr
5) What is the concentration of 10.00 mL of HBr if it takes 16.73 mL of a 0.253 M
LiOH solution to neutralize it?
: 0. 253 M / 0. 01673 L = x M / 0.01 L
x
= 0. 253 ( 0. 01 ) / 0. 01673
x
= 0. 151 Mol
2. Data Sheet
Concentration of sodium hydroxide: 0.01 M
Balanced Chemical Equation of the titration reaction:
NaOH + HCl => H2O + NaCl
Phenolphthalein
Bromophenol blue
Trial 1
Trial 2
Trial 3
Trial 1
Trial 2
Trial
Initial buret
volume (mL)
20.9 mL
25.3 mL
20.2 mL
20.1 mL
23.9 mL
20.2 mL
Final buret
volume (mL)
25.4 mL
29.6 mL
24.6 mL
23.9 mL
27.5 mL
23.5 mL
Volume of base
(mL)
25.4-20.9
=
4.5 mL
29.6-25.3
=
4.3 mL
24.6-20.2
=
4.4 mL
23.9-20.1
=
3.8 mL
27.5-23.9
=
3.6 mL
23.5-20.2
=
3.3 mL
Volume of base
(L)
4.5/1000
=
0.0045 L
4.3/1000
=
0.0043 L
4.4/1000
=
0.0044 L
3.8/1000
=
0.0038 L
3.6/1000
=
0.0036 L
3.3/1000
=
0.0033 L
Moles of base
(mol)
0.01M x
0.0045 L
=
0.000045
mol
0.01 M x
0.0043 L
=
0.000043
mol
0.01 M x
0.0044 L
=
0.000044
mol
0.01 M x
0.0038 L
=
0.000038
mol
0.01 M x
0.0036 L
=
0.000036
mol
0.01 M x
0.0033 L
=
0.000033
mol
Acid to Base
Mole Ratio
1:1
1:1
1:1
1:1
1:1
1:1
Moles of acid
(mol)
0.000045
mol
0.000043
mol
0.000044
mol
0.000038
mol
0.000036
mol
0.000033
mol
Volume of acid
(L)
10 mL
/1000
=
0.01 L
10 mL
/1000
=
0.01 L
10 mL
/1000
=
0.01 L
10 mL
/1000
=
0.01 L
10 mL
/1000
=
0.01 L
10 mL
/1000
=
0.01 L
Acid
concentration (M)
Average
concentration (M)
0.000045
mol / 0.01
L=
0.0045 M
0.000043
mol / 0.01
L=
0.0043 M
0.000044
mol / 0.01
L=
0.0044 M
(0.0045 + 0.0043 + 0.0044) / 3
= 0.0044 M
0.000038
mol / 0.01
L=
0.0038 M
0.000036 0.000033
mol / 0.01 mol / 0.01
L=
L=
0.0036 M 0.0033 M
(0.0038 + 0.0036 + 0.0033) / 3
= 0.003567 M
Discussion
1. Postlab question
1) How would it affect your results if you used a beaker with residual water in it to
measure out your standardized sodium hydroxide solution?
: If we used a beaker with residual water, there is a possibility that it makes the
concentration and color of the solution inaccurate.
2) How would it affect your results if you used a wet Erlenmeyer flask instead of a dry
one when transferring your acid solution from the volumetric pipette?
: There is a chance that the Erlenmeyer flask is coated with another solution other
than water, which could also cause some mistakes or discrepancies in the recorded
data, for example:
The endpoint of the solution changes (the color will change quicker or slower
than it should be)
- The solution is contaminated.
- The concentration of HCl and NaOH that we calculate will be inaccurate.
3) How do you tell if you have exceeded the equivalence point in your titration?
-
: When the color of each solution overchange
- Phenolphthalein: the color change to pink (over than light pink)
- Bromophenol blue: the color change to purple (over than gray)
4) Vinegar is a solution of acetic acid (CH3COOH) in water. For quality control
purposes, it can be titrated using sodium hydroxide to assure a specific %
composition. If 25.00 mL of acetic acid is titrated with 9.08 mL of a standardized
2.293 M sodium hydroxide solution, what is the molarity of the vinegar?
: 9.08x2.293/25 = 0.833M
Vinegar molarity: 0.833 M
2. Error
1) We dropped NAOH a little too much, as a result, the color didn’t come out as
accurate. For example, we wanted the color of the solution to be light pink and graygreen as much as possible.
2) The Burette is not vertically upright to the table, so this made us read the number
wrong.
3) We were not expert, so when we mix the chemical we do it not good enough and
sometimes not stable.
4) The HCl in the beaker was a little bit not equal to each other so the number of NaOH
that we drop will not be the same.
Conclusion
From the experiment and calculation, the solution with phenolphthalein will change
color from transparent to light pink when it reaches pH 9. The concentration that we obtain is
0.0044 M. The solution with bromophenol blue will to gray once it reaches pH 4. The
concentration is 0.003567 M. Comparing both results, the concentration with the
phenolphthalein indicator is only very little higher.
Phenolphthalein indicator
Bromophenol blue indicator
Suggestion
1. Be more careful in emitting the solution from the pipette into the beaker so that it
wouldn’t be too concentrated/cause any mistake.
2. Hold the equipment/appliances more carefully to reduce the risk of them falling down
and being broken.
3. Make sure you wear the glasses, gloves, and lab coat before doing the experiment to
prevent skin irritation from direct contact with the solution.
References
Helmenstine, M.H. (2017). Titration Definition (Chemistry). Retrieved 27 February, 2018,
from https://www.thoughtco.com/titration-definition-602128
National Center for Biotechnology Information. PubChem Compound Database; CID=313 .
Retrieved 19 February, 2018, from https://pubchem.ncbi.nlm.nih.gov/compound/313
National Center for Biotechnology Information. PubChem Compound Database; CID=14798,
Retrieved 19 February, 2018, from https://pubchem.ncbi.nlm.nih.gov/compound/14798
The editors of encyclopædia britannica. (n.d.). Titration. Retrieved 19 February, 2018, from
https://www.britannica.com/science/titration
Wilson, B. (2017). Acid-Base Indicators. Retrieved 27 February, 2018, from
https://www.carolina.com/teacher-resources/Interactive/acid-base-indicators/tr10647.tr
Worklog
Student
Work
Apitta Kanchanapuping (Pao)
-
Abstract
Reference
Result (pre-lab)
Conclusion
Nathapat Jaihow (Pooh)
-
Introduction
Post-lab questions
Suggestion
Natwadee Nim-aussornkul (Dear)
-
Glassware
Thunchanok Intachot (Earn)
-
Flowchart
Post-lab
Error
Kannicha Eksuwancharoen (Dream)
-
Datasheet
Calculation
Warit Ittisomboon (Heart)
-
Error
Pre-lab (calculation question)
Post-lab (calculation question)