Experiment 2:
Aim: To determine the strength of ammonia in given sample of water.
Apparatus Required: - Pipette, Burette, Funnel, Conical flask, Volumetric flask, and
Dropper.
Chemical Required: - Standard N/50 Na2CO3, HCl solution, Water sample, and
Methyl orange (indicator)
Theory: - Ammonia is found as ammonium hydroxide solution. It is formed when
ammonia gas dissolved in water as:
NH3 (g) + H2O (l) NH4OH (aq)
where NH3 is originated from the pesticide, insecticides fertilizer and other industrial
waste that are disposed into water bodies.
The titration of NH3 and HCl is called Acid-Base titration. Here, HCl is not a primary
standard solution. So it is firstly standardized by titrating with Na2CO3 solution.
Indicator: - Methyl Orange.
The end point: Yellow to light pink colour.
Procedure:
Standardization of HCl solution: (HCl / Na2CO3)
1. Rinse and fill the burette with HCl.
2. Pipette out 10 ml of Na2CO3 solution into conical flask and added 2 drops of
Methyl orange.
3. Titrated with HCl solution till colour change from yellow to light pink.
4. The experiment was repeated three times to get concordant readings.
Titration of water sample with HCl solution:- (HCl / Water)
1. Rinse and fill the burette with HCl.
2. Pipette out 10 ml water sample in conical flask.
3. Added 2-3 drops of Methyl orange and titrate with HCl solution till the colour
change from yellow to light pink.
4. The experiment was repeated three times to get concordant reading.
Observations: -
Standardization of HCl solution:-
S.No. Vol. of Na2CO3 Burette Reading Volume of HCl
sol.in conical Initial Reading Final Reading used (ml)
flask (ml)
Calculation: -
N1 = Normality of HCl, V1 = Volume of HCl
N2 = Normality of Na2CO3 solution, V2 = Volume of Na2CO3 solution
N1V1 = N2V2
(HCl) (Na2CO3)
N1 X 10 = (1/50) X Volume of Na2CO3 used
N1 = ______________N
Therefore, Normality of HCl = _________N
Titration of water sample with HCl solution:
S.No. Vol. of water Burette Reading Volume of HCl
sample conical Initial Reading Final Reading used (ml)
flask (ml)
Calculation –
N3 = Normality of water, V3 = Volume of water
N1 = Normality of HCl solution, V4 = Volume of HCl solution
N3V3 = N1V4
(Water) (HCl)
N3 X 10 = N1 X Volume of HCl used
N3 = ______________N
Therefore, Normality of water = _________N
Strength of NH3 in water = Equivalent weight of NH3 X Normality of Water
= 17 g X _____N
= ________ g/l
= ________ X 1000 ppm
Result:
Normality of HCl = _______N
Normality of Water = _______N
Strength of NH3 = _______g/l
Precautions:
1. Handle the apparatus carefully.
2. Do no pipette out hot solutions.
3. There should no air bubbles in burette
4. Lower meniscus of HCl solution be observed.
Viva Questions
Q1: What method was used to determine the strength of ammonia in the given
sample of water?
Sol: Strength of ammonia in a given sample of water can be measured volumetrically
through titration. In this method, a known volume of the water sample is titrated with a
standardized solution of an acid, typically Hydrochloric acid (HCl), in the presence of
an indicator, methyl orange, which changes colour at the endpoint of the titration.
Q2: Can you explain the principle behind the volumetric measurement of
ammonia in sample of water?
Sol: The principle behind the volumetric measurement of ammonia in a sample of
water is based on acid-base titration. Ammonia (NH3) is a weak base, and it reacts
with acids to form ammonium ions (NH4+). In the titration process, a known volume of
the water sample containing ammonia is titrated with a standardized solution of an
acid such as standard solution of Hydrochloric acid.
NH3 + HCl NH4Cl
The endpoint of the titration occurs when all the ammonia in the water sample has
reacted with the Hydrochloric acid. At this point, the solution becomes neutral, and
further addition of acid make the solution acidic which can be detected using an
indicator that changes color when the solution reaches a certain pH.
Q3: What is pH of ammonia?
Sol: Typically, the pH of an ammonia solution will be between 11 and 12, compared
with a pH of about 14 for sodium hydroxide solutions.
Q4: What is IUPAC name of Ammonia?
Sol: IUPAC name of Ammonia is Azane.
Q5: Is ammonia an acid or base?
Sol: Ammonia is a typical weak base. Ammonia itself obviously doesn't contain
hydroxide ions, but it reacts with water to produce ammonium ions and hydroxide ions.
Q6: How do you detect ammonia in an experiment?
Sol: We can dip a glass rod into concentrated hydrochloric acid and hold it near the
mouth of a vessel containing what we suspect is ammonia gas. If we allow the vapor
produced from concentrated hydrochloric acid, HCl, to mix with the gas produced from
the reaction, a dense white vapor will form if the gas is ammonia.
Q7: How does the strength of ammonia in a water sample affect its properties?
Sol: Ammonia concentration in water affects its properties, including pH, odour, the
solubility of metals, toxicity to aquatic organisms, corrosion, cleaning properties, and
chemical reactions. It is an essential factor to consider for environmental monitoring,
water treatment, and various industrial processes.
