1. CHEM10101 Introductory Chemistry
Answer:
Introduction :
According to the definition of Arrhenius : “An acid ionizes in water to give a Hydrated
proton( indicated as H3O+ or H+), a base ionizes in water to give hydroxide ion(OH-)”. Also,
according to the definition of Bronsted-Lowry : “An acid is a proton donor, a base is a proton
acceptor”.
In aqueous solutions, Strong acids dissociate completely to form hydronium ions (H3O+) .
On the other hand, weak acids in aqueous solutions dissociates partially to form hydronium
ions (H3O+) and the extent to which it dissociates depends on the equilibrium constant (Ka)
of the acid.
HA + H2O H3O+ + A- (Dissociation of strong acid in water)
HA + H2O H3O+ + A- (Dissociation of weak acid in water)
The strength of an acid is dependent on the proposition of itself, that has reacted with water
(H2O) to produce ions and this is characterised by the term known as pH values. pH is a
measurement of the concentration of the Hydrogen ions in a solution. The lower the pH
value is, higher is the concentration of hydrogen ions in the solution.
pH = -log[H3O+]
The position of the equilibrium decides the strength pf weak acids, which in turn is reflected
by the equilibrium constant (Ka). Between the reaction of acid and water, the position of
equilibrium of the reaction varies from acid to acid (weak or strong acids). The further to
the left of the reaction it lies, meaning less dissociation of Hydrogen ions, the weaker is the
acid. The strength of weak acids is measured using the quantity known as pKa, which is
related to Ka as shown below. The greater the value of the pKa , the stronger is the acid.
pKa = -log[Ka]
2. pH = pKa + log([A-]/[HA])
An acid base titration is the determination of the concentration of an acid or base by exactly
neutralising the acid or base with another acid or base of known concentration. Typically,
the titrant is added through a burette to a known volume of the analyte until the reaction is
complete. Knowing the volume of the titrant added allows us to determine the
concentration of the unknown Analyte. A pH meter is used to measure the pH as the titrant
is added in small increments(0.1 mL) to the analyte. A graph is plotted with pH along the
vertical axis and volume of the titrant added along the horizontal axis, and curve is obtained
which is nothing but the Titration Curve.
When an acidic solution is titrated with a basic solution, the pH of the acidic solution is
initially low. As base is added, the change in pH is gradual until close to the equivalence
point, when equimolar amounts of acid and base have been mixed and the products of the
reaction are salt and water. Near the equivalence point, the pH increases very rapidly. The
change in pH then becomes more gradual again, before levelling off with the addition of
excess base.
HA(aq) + BOH(aq) H2O(l) + BA(aq)
When a weak acid is titrated with a strong base, the pH of the acidic solution is initially low
but higher than the initial pH of the strong acid. As base is added, the pH changes slowly and
gradually. This indicates the formation of buffer system as the titration approaches the
equivalence point. Another significant volume during a titration is when the number of
moles of acid (HA) remaining is exactly equal to the number of moles if conjugate base (A-)
produced. This point is called the “Half Equivalence Point” because it occurs when exactly
half the weak acid has been titrated. Using Henderson – Hassel Balch equation –
pH = pKa
Apparatus Required :
Funnel, stir bars, Magnetic stirrer, CH3COOH solution of 0.10 M concentration, HCl solution
of 0.10 M concentration, Sodium Hydroxide solution of unknown concentration, Wash
bottle with ultra-pure water for rinsing the probe, measuring cylinder, five 100 mL beakers,
a 50 mL burette, Standard buffers of pH 4.0, pH 7.0 and pH 10.0, pH meter, etc.
Strong Acid Titration :
pH meter is standardized using the provided standard buffers.
50 mL of the HCl solution is obtained in a clean, dry beaker. The beaker is labelled.
Small amount of HCl solution is used to rinse another beaker. The rinsing solution is
discarded into the sink.
Small amount of HCl solution is used to rinse the measuring cylinder. The rinsing solution is
3. discarded into the sink.
20 mL of the HCl solution is added to the measuring cylinder and the solution is transferred
to the second beaker. The beaker is labelled as : “HCl solution for Titration”.
100 mL of NaOH solution is obtained in another clean, dry beaker. The beaker is labelled.
Small amount of NaOH solution is used to rinse the burette. The rinsing solution is
discarded into the sink.
The burette is filled with the NaOH solution to a point higher than the 0.00 line the excess of
NaOH solution is allowed to flow into a waste container until the meniscus is on the 0.00
line.
A magnetic stirrer is carefully dropped into the beaker containing the HCl solution. The
beaker is set on the magnetic stirrer and the burette containing NaOH solution and the pH
electrode is positioned.
Stirring is carefully turned on and it is made sure that the electrode doesn’t hit the stirrer.
pH of the HCl solution is measured and recorded.
1 mL of NaOH solution is added from the burette and the pH is measured.
NaOH is added recurrently in amount of 0.1 mL until the pH reading become greater than
12.
Weak Acid Titration :
50 mL of 0.10 M CH3COOH solution is obtained in a clean, dry beaker and the beaker is
labelled.
A small amount of the acetic acid is used to rinse another beaker. The rinsing solution is
discarded into the sink.
The measuring cylinder is rinsed twice with deionized water and is followed by a small
amount of the acetic acid solution. The rinsing solution is discarded into the sink.
20 mL of the acetic acid solution is added to the measuring cylinder and then transferred to
another beaker. The beaker is labelled as :”CH3COOH solution for Titration”.
Burette is filled with NaOH solution to a point higher than the 0.00 line and then the NaOH
solution is allowed to leave slowly till the meniscus is on the 0.00 line.
A magnetic stirrer is carefully dropped into the beaker containing the acetic acid solution.
The beaker is set on the magnetic stirrer and the burette containing NaOH solution and the
pH electrode is positioned.
Stirring is carefully turned on and it is made sure that the electrode doesn’t hit the stirrer.
pH of the acetic acid solution is measured and recorded.
1 mL of NaOH solution is added from the burette and the pH is measured.
NaOH is added recurrently in amount of 0.1 mL until the pH reading become greater than
12.
Observations :
pH values from the titration of HCl with NaOH :
VNaOH(mL) added
17. 30
12.37
Graph :
For 1st table, graph is shown below-
For 2nd table, graph is shown below-
Calculations :
From the 1st graph :
Calculating concentration of NaOH solution –
MNaOHVNaOH = MHClVHCl
MNaOH(18.47) = (0.10)(20)
MNaOH =
= 0.108 M
Molarity of NaOH comes out to be 0.108 M
From the second graph,
pKa = pH = 4.988
Ka = 10-pH
= 10-4.988
= 1.028 x 10-5 units
Equilibrium constant for the neutralisation reaction of acetic acid (CH3COOH) and Sodium
Hydroxide (NaOH) comes out to be 1.028 x 10-5 units.
Results :
Using Titration for unknown concentration of base(NaOH) using HCL of known
18. concentration and volume, the concentration of NaOH is calculated as 0.108 M. Also, using
acetic acid(weak acid) in the process of titration, the equilibrium constant comes out to be
1.028 x 10-5 units.
Precautions And Sources Of Error :
All these chemicals with given concentration may cause skin burns. Therefore, these must
be handled with care.
Eye glasses must be used during the lab process.
Discharge from the burette must be made drop by drop in order to avoid missing the
equivalence point.
The waste chemicals must be disposed properly.
References :
Atkins P.(2018), Physical Chemistry, New York, Wiley Publications
![CHEM10101 Introductory Chemistry
Answer:
Introduction :
According to the definition of Arrhenius : “An acid ionizes in water to give a Hydrated
proton( indicated as H3O+ or H+), a base ionizes in water to give hydroxide ion(OH-)”. Also,
according to the definition of Bronsted-Lowry : “An acid is a proton donor, a base is a proton
acceptor”.
In aqueous solutions, Strong acids dissociate completely to form hydronium ions (H3O+) .
On the other hand, weak acids in aqueous solutions dissociates partially to form hydronium
ions (H3O+) and the extent to which it dissociates depends on the equilibrium constant (Ka)
of the acid.
HA + H2O H3O+ + A- (Dissociation of strong acid in water)
HA + H2O H3O+ + A- (Dissociation of weak acid in water)
The strength of an acid is dependent on the proposition of itself, that has reacted with water
(H2O) to produce ions and this is characterised by the term known as pH values. pH is a
measurement of the concentration of the Hydrogen ions in a solution. The lower the pH
value is, higher is the concentration of hydrogen ions in the solution.
pH = -log[H3O+]
The position of the equilibrium decides the strength pf weak acids, which in turn is reflected
by the equilibrium constant (Ka). Between the reaction of acid and water, the position of
equilibrium of the reaction varies from acid to acid (weak or strong acids). The further to
the left of the reaction it lies, meaning less dissociation of Hydrogen ions, the weaker is the
acid. The strength of weak acids is measured using the quantity known as pKa, which is
related to Ka as shown below. The greater the value of the pKa , the stronger is the acid.
pKa = -log[Ka]](https://image.slidesharecdn.com/chem10101introductorychemistry-230318021540-6a48a164/85/CHEM10101-Introductory-Chemistry-docx-1-320.jpg)
![pH = pKa + log([A-]/[HA])
An acid base titration is the determination of the concentration of an acid or base by exactly
neutralising the acid or base with another acid or base of known concentration. Typically,
the titrant is added through a burette to a known volume of the analyte until the reaction is
complete. Knowing the volume of the titrant added allows us to determine the
concentration of the unknown Analyte. A pH meter is used to measure the pH as the titrant
is added in small increments(0.1 mL) to the analyte. A graph is plotted with pH along the
vertical axis and volume of the titrant added along the horizontal axis, and curve is obtained
which is nothing but the Titration Curve.
When an acidic solution is titrated with a basic solution, the pH of the acidic solution is
initially low. As base is added, the change in pH is gradual until close to the equivalence
point, when equimolar amounts of acid and base have been mixed and the products of the
reaction are salt and water. Near the equivalence point, the pH increases very rapidly. The
change in pH then becomes more gradual again, before levelling off with the addition of
excess base.
HA(aq) + BOH(aq) H2O(l) + BA(aq)
When a weak acid is titrated with a strong base, the pH of the acidic solution is initially low
but higher than the initial pH of the strong acid. As base is added, the pH changes slowly and
gradually. This indicates the formation of buffer system as the titration approaches the
equivalence point. Another significant volume during a titration is when the number of
moles of acid (HA) remaining is exactly equal to the number of moles if conjugate base (A-)
produced. This point is called the “Half Equivalence Point” because it occurs when exactly
half the weak acid has been titrated. Using Henderson – Hassel Balch equation –
pH = pKa
Apparatus Required :
Funnel, stir bars, Magnetic stirrer, CH3COOH solution of 0.10 M concentration, HCl solution
of 0.10 M concentration, Sodium Hydroxide solution of unknown concentration, Wash
bottle with ultra-pure water for rinsing the probe, measuring cylinder, five 100 mL beakers,
a 50 mL burette, Standard buffers of pH 4.0, pH 7.0 and pH 10.0, pH meter, etc.
Strong Acid Titration :
pH meter is standardized using the provided standard buffers.
50 mL of the HCl solution is obtained in a clean, dry beaker. The beaker is labelled.
Small amount of HCl solution is used to rinse another beaker. The rinsing solution is
discarded into the sink.
Small amount of HCl solution is used to rinse the measuring cylinder. The rinsing solution is](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)