2 Determining the Concentration of Ammonia in Window Cleaner Solution

Sunny Ng Wing Lam
G10L (20)
Chemistry A Lab 10.2 Determining the Concentration of Ammonia in Window Cleaner Solution
Design (D)
Aim
To determine the concentration of ammonia, NH3, in the commercial window cleaner solution
Background
Window cleaner contains ammonia, NH3, a weak base, which helps remove dirt from glassware. The concentration of ammonia in the window cleaner solution varies by brands. Titrating the window cleaner solution with an acid of known concentration allows us to calculate the concentration of the ammonia in that brand of window cleaner solution.
In this experiment, you will be titrating a diluted window cleaner solution of unknown concentration against sulfuric acid of known concentration. The titrant will be the sulfuric acid and the analyte will be the diluted window cleaner solution. Methyl orange will be used as the pH indicator of this reaction.
Apparatus
 Burette, 50 cm3
 Small beaker / Weighing bottle
 Burette stand
 Wash bottle
 Conical flask, 100 cm3
 Dropper
 Volumetric flask, 250 cm3 with stopper
 Funnel
 Volumetric pipette, 25 cm3
 Standardized sulfuric acid, H2SO4(aq), ~ 0.01 M
 Pipette filler
 Window cleaner solution
 White tile
 Methyl orange
Procedures
Part A Preparation of the diluted window cleaner solution
1. Wash the glassware with water and appropriate solutions.
2. Pipette 25 cm3 of the window cleaner solution to a 250 cm3 volumetric flask.
3. Add water to fill the flask to the graduation.
4. Stopper and invert the flask to mix the content thoroughly.
Part B Titration between sulfuric acid and ammonia
1. Fill the burette with sulfuric acid.
2. Pipette 25 cm3 of the diluted window cleaner solution to a pre-cleaned conical flask.
3. Add 2 drops of methyl orange into the conical flask, swirl and mix the content.
4. Titrate the diluted window cleaner solution against the standardized sulfuric acid.
5. Repeat part B step 1 – 4 for 3 more times.
Data Collection and Processing (DCP)
Raw Data
The following are the data recorded during the experiment.
Concentration of Sulfuric Acid, H2SO4(aq): 0.0122M
Volume of Window Cleaner Solution added into volumetric flask: 25.00cm3 ± 0.03cm3
Volume of diluted Window Cleaner Solution, NH3(aq), in volumetric flask: 250.00cm3 ± 0.15cm3
Volume of diluted Window Cleaner Solution, NH3(aq), added into conical flask: 25.00cm3 ± 0.03cm3
Initial and Final Volumes of Sulfuric Acid, H2SO4(aq), before and after naturalizing 25cm3 of diluted Window Cleaner Solution:

Rough Trial
Trial 1
Trial 2
Trial 3
Initial Volume (cm3)
(± 0.05 cm3)
16.50
30.50
18.90
33.60
Final Volume (cm3)
(± 0.05 cm3)
30.50
44.80
33.60
48.20

Processed Data
In the experiment, the following reaction, as shown below, occurred:
2NH3(aq) + H2SO4(aq) (NH4)2SO4(aq)
Sulfuric Acid, H2SO4(aq), was added into diluted Window Cleaner Solution, NH3(aq). It neutralized the solution it and the product formed was Ammonium Sulfate Solution, (NH4)2SO4(aq).
To find out the concentration of ammonia, NH3, in the window cleaner solution, we have to do some calculation steps.
Step 1:
Firstly, we have to find out the volume of sulfuric acid, H2SO4(aq), used to naturalize 25cm3 of the diluted Window Cleaner Solution, NH3(aq). As the unit of concentration (M) is mol/dm3, we have to convert the units of all volumes from cm3 into dm3 for calculations.

Rough Trial
Trial 1
Trial 2
Trial 3
Initial Volume (dm3)
(± 0.00005 dm3)
0.01650
0.03050
0.01890
0.03360
Final Volume (dm3)
(± 0.00005 dm3)
0.03050
0.04480
0.03360
0.04820
Volume Used (dm3)
(± 0.00010 dm3)
0.01400
0.01480
0.01470
0.01460
Average Volume Used (dm3)
(± 0.00010 dm3)

0.01470

Step 2:
Secondly, we have to find out the number of moles of H2SO4.
Number of moles of H2SO4
= Concentration of H2SO4 × Volume of H2SO4
= 0.0122 × 0.01470
= 0.00017934 moles (± 0.680%) (3 s.f.)

Step 3:
Thirdly, we have to find the number of moles of NH3 in the diluted window solution used in the each titration, i.e. 25 cm3 of diluted window solution.
As the moles ratio of NH3 : H2SO4
= 2:1
Therefore, the number of moles of NH3 in 25 cm3 of diluted window solution
= number of moles of H2SO4 × 2
= 0.00017934 × 2
= 0.00035868 moles (± 0.680%) (3 s.f.)

Step 4:
Next, we can also find the concentration of NH3 in the diluted window cleaner solution by the following steps:
Concentration of NH3 in the diluted window cleaner solution
=
=
= 0.0143472M (± 0.800%) (3 s.f.)

Step 5:
Afterwards, we have to find out the number of moles of NH3 in the whole flask of diluted window cleaner solution, i.e. 250cm3 of diluted window cleaner solution.
Number of moles of NH3 in 250cm3 of diluted window solution
= Concentration of NH3 × Volume of NH3
= 0.0143472 × 0.250
= 0.0035686 moles (± 0.860%) (3 s.f.)

Step 6:
Lastly, we can calculate the concentration of ammonia, NH3, in the window cleaner solution.
As deionized water, H2O(l), was added to dilute the 25cm3 of window cleaner solution and it contains 0 moles of NH3, the 25cm3 of window cleaner solution should also contain 0.0035686 moles of NH3.
Therefore, concentration of NH3 in the window cleaner solution
=
=
= 0.143472 M (~0.143M) (± 0.980%) (3 s.f.)

Physical Observations
When 2 drops of methyl orange was added into the diluted window cleaner solution in the conical flask, the drops spread out throughout the solution extremely slowly. After swirling and mixing, the solution turned light yellow.
When the sulfuric acid, H2SO4(aq), was slowly added into the conical flask, the color of the solution gradually turned from light yellow to a bit of light pink. Suddenly, when a certain amount of sulfuric acid, H2SO4(aq), was added and the solution was neutralized , the color of the solution turned pale pink.
The colors of the methyl orange in the solutions might be affected as the color of the window cleaner solution is blue originally.
Conclusion and Evaluation (CE)
After conducting this experiment, it could be said that the aim was fulfilled and the results were reasonable.
The aim of this experiment was to figure out the concentration of ammonia in a commercial window cleaner solution.
At the beginning of the experiment, we diluted 25cm3 of window cleaner solution and created a 250cm3 of diluted window cleaner by adding deionized water. Then we pipetted 25cm3 of the diluted water cleaner solution for each titration and found out that 14.70cm3 of sulfuric acid, H2SO4(aq), is needed to neutralize the solution. As we know the concentration and volume of the sulfuric acid, H2SO4(aq), we can also found its number of moles, which is 0.00017934 moles. Next, using the ratio in the balanced equation of the reaction, we can also find the number of moles of NH3 in the 25cm3 of diluted window cleaner solution, which is 0.00035868 moles. After that, we can find the concentration of 25cm3 of diluted window cleaner solution to be 0.0143472M . Knowing that the concentration does not change, we can also find out that the number of moles of NH3 of 250cm3 of diluted window cleaner solution in the volumetric flask is 0.0035686 moles. Because deionized water does not contain any number of moles of NH3, the number of moles of NH3 will also be 0.0035686 moles in the 25cm3 of window cleaner solution. Lastly, we can find the concentration of ammonia, NH3, in the window cleaner solution: 0.143472M (~0.143M).
The uncertainties of the experiment are calculated step by step, as follows (using cm3).
Step 1:
Uncertainty = 0.05 × 2 = ± 0.10cm3
As the value is calculated by subtracting two values measured by the burette, the uncertainty of the answer shall be multiplied by 2.
Step 2:
Uncertainty = 0.680% (3 s.f.)
As the uncertainty of the Concentration of H2SO4 is not given, the uncertainty of the Volume of H2SO4 would be considered only.
Step 3:
Uncertainty 0.680% (3 s.f.)
As there is no uncertainty for the ratio 1:2, the uncertainty of the previous step will be used.
Step 4:
Uncertainty = 0.680% + () = ± 0.800% (3 s.f.)
The uncertainty of the Volume of NH3 used for each titration is added to the previous uncertainty. As the equipment used to measure the volume was the pipette, the uncertainty of the pipette will be used.
Step 5:
Uncertainty = 0.800% + () = ± 0.860% (3 s.f.)
The uncertainty of the Volume of NH3 in the volumetric flask is added to the previous uncertainty. The uncertainty of the volumetric flask will be used.
Step 6:
Uncertainty = 0.860% + () = ± 0.980% (3 s.f.)
The uncertainty of the volume of window cleaner solution added into the volumetric flask is added to the previous uncertainty. As the equipment used to measure the volume was the pipette, the uncertainty of the pipette will be used. This is the final uncertainty of the experiment.
The percentage uncertainty for this experiment (0.980%) is relatively low, which is good and makes the data more reliable. The reason behind is because the apparatus used in the experiment had very small uncertainties. For example, the pipette used only had an uncertainty of 0.03cm3, the burette had an uncertainty of 0.05cm3 and the volumetric flask’s was only 0.15cm3. Therefore, the apparatus used were well chosen and would make sure that uncertainties play a very insignificant role in the experimental results.
Though this experiment could be called a successful one, due to the high credibility of the data, there are some things that could have been done better. The following are some modifications for this experiment.
Problem on Experiment
Effect on Results
Possible Improvement
When the diluted window cleaner solution was prepared, there were some bubbles floating on the surface. There were also some bubbles stuck at the bottom of the burette.
The bubbles floating on the surface would be blocking our sight from seeing the line that marks the volume of the solution on the apparatus. The meniscus cannot be seen clearly too. This would affect the precision as the volume recorded would be inaccurate and thus affecting the final results.
If bubbles appear in the pipette, release the solution and suck up the solution again until there are no bubbles. If bubbles appear in the burette, keep on letting the liquid flow down until the bubbles disappear.
The color change of the solution at the near end of the titration was too sudden.
We might not react quick enough to rotate the stopcock and stop the flow of sulfuric acid. The amount of sulfuric acid recorded might exceed the actual value needed.
The rate of addiction should be controlled. The stopcock should be adjusted so that the flow of sulfuric acid is slow enough (for us to see each drop mixed with the solution).
The solutions might be contaminated.
The concentration of and number of moles in that solution will be affected and the results recorded would vary.
The apparatus, like the pipette and the conical flask, must be washed thoroughly after each trial. The same pipette must not be used to contain both solutions without being washed before and after.
The reaction between a weak and diluted acid and base would make it very hard to determine the exact equivalence point.
It would make it not easy for us to find the equivalence point.
Stronger and more concentrated acids and bases should be used instead. However, they have to be handled with great care.
The indicator, Methyl orange, did not have a very dramatic color change at the end point. (This occurred because the diluted window cleaner solution had a light blue color).
It might be hard to precisely see when the solution has actually changed its color completely. The end point recorded might not be accurate.
Another indicator, which has a dramatic change in color, could be used to replace methyl orange. It should also change its color at the end point (equivalence point is exactly at end point).
The Mixing of 25cm3 of window cleaner solution with deionized water (to form diluted window cleaner solution) might not be mixed well.
The concentration of diluted window cleaner solution for each trial might vary and affecting final results.
The mixing must be done thoroughly by swirling and inverting the volumetric flask so the concentration of ammonia can be spread equally. More time good be given as well.
The burette and/or pipette was/were washed with the wrong solution.
The (for example water) would remain on the walls of the burette and thus affecting the concentration of titrant. The results would vary.
The burette and pipette should be rinsed with the correct solution. (If this was not a quiz, the instructions would guide the steps clearly).
Not all the liquid were transferred into the flasks. Some dropped out from the pipette.
The actual volume and number of moles might vary from the original and the final calculated results might be inaccurate.
The pipette has to be transferred quickly from one beaker to another flask to make sure it does not drop any liquid. The beakers and flasks can be placed close together.
The conical flask is swirled too vigorously.
Some of the solution might splash out of the table before the end point had been reached. Some of the titrant might land on the table instead of inside the flask. The volumes recorded might vary.
The conical flask should not be swirled too vigorously. The flow of the titrant can be adjusted to a slower rate as well.
The meniscus was hard to see (especially in the pipette and burette). It was not easy for the meniscus to stop at the exact point.

Misreading of the volumes may occur. The final results might vary as a result.
The meniscus must be viewed at the same level with the eye. If possible, more advanced equipment could be used for the experiment to reduce such human error.

~~~~~THE END~~~~~