Chemistry uncertainty conical flask

Chemistry Lab Report
Design
Research question: how to find the absolute uncertainty of a conical flask?

Variables: Independent variable: volume of water to be measured Dependent variable: mass of water Controlled variable: temperature wind speed type of chemical solution (water)

Apparatus: A 100 mL conical flask
A 4 decimal place electronic balance
Distilled water
A 250 mL beaker
A dropper
Tissue paper

Procedure:
1) The conical flask was weighted with the balance and the value was recorded.
2) The beaker was filled with distilled water and the water was added into the conical flask up to the 60 mL mark. The dropper was used when water level was approaching the 60 mL mark.
3) The weight of the conical flask containing water was recorded.
4) The mass of water was found by subtracting the weight of conical flask from the weight of conical flask with water.
5) The volume of water was found from the mass of water .
6) Steps 1) to 5) were repeated ten times.
7) 60 mL was subtracted from each of the calculated volume of water.
8) The data obtained from step 7) were compared with each other and the largest value was taken as the absolute uncertainty of the conical flask.

-The volume of water poured into the conical flask was being decided while the uncertainty of the conical flask, calculated from the experimental volume subtracting theoretical volume of water, was being investigated.
-The same conical flask and electronic balance was used throughout the experiment to ensure the results were not to be affected by the difference in apparatus used. -The volume readings were taken from the bottom of the meniscus of liquid and it was made sure all the liquid was emptied to ensure accurate reading of volume.
- A dropper was used when the water level approached 50 mL mark of the conical flask to prevent solution from overflowing the mark and to ensure accurate reading of volume of solution.
-Only distilled water was used in the experiment to access fair results in all rounds of experiments.
-The uncertainties of the balance were neglected because the value (±0.0001g) was too small and has very little effect on the results. -10 sets of data were taken into account for more accurate results. -The experiment was done in room temperature and in an environment of same wind speed to prevent the experimental results from being affected.
-The exterior and the upper 1/3 part of the interior of the conical flask was wiped dry with tissue paper before every set of experiment was carried out to assure accurate measurement of the mass of water contained.
-The density of water is assumed to be 1 g/dm³.
Data Collection and Presentation

(A) Mass of conical flask used: 66.7258 g

Observations: -The value displayed on the balance sometimes fluctuated within 0.0004 g when the conical flask with water was being weighed.

Tables of Results

Rough Collected Data (corrected to 4 d.p.)
Experiment
round
Mass of conical flask together with water up to 60mL mark (g)
1
124.3510
2
124.6126
3
124.5128
4
125.0068
5
125.6183
6
124.5978
7
124.9737
8
124.3511
9
125.6626
10
125.9358

Processed Data (corrected to 4 d.p.)
Experiment
round
Mass of conical flask together with water up to 60mL mark (g)
(M) Mass of water(g)
= Volume of water
(cm³)
Difference in mass of water from theoretical value (M-60)
1
124.3510
57.5982
-2.4018
2
124.6126
57.8868
-2.1132
3
124.5128
57.7600
-2.2400
4
125.0068
58.2540
-1.7460
5
125.6183
58.8925
-1.1075
6
124.5978
57.8720
-2.1280
7
124.9737
58.2479
-1.7521
8
124.3511
57.6253
-2.3747
9
125.6626
58.9368
-1.0632
10
125.9358
59.2100
-0.7900

The mass of water (M) was obtained by “mass of conical flask together with water up to 60mL mark - mass of conical flask used (A)”; the difference in mass of water from theoretical value (D) was obtained by M-60. The largest absolute value of D was taken as the absolute uncertainty of the conical flask as it is the greatest difference from the theoretical value.

Therefore,
Absolute uncertainty of a 100mL conical flask
= 2.4018 mL
= 2 mL (1 s.f.)

The result of the experiment has shown that the uncertainty of a 100mL conical flask is 2mL. Comparing to a 100 mL volumetric flask, which has absolute uncertainty of 0.08mL, a conical flask is rather uncertain and will give inaccurate results. This explains why a conical flask is usually used for holding chemicals (for example in titration, it is used for containing the solution being titrated against and the indicator) instead of used for giving measurements.
In this experiment, an observation was that the value displayed on the balance fluctuated within 0.0004 g. This observation was noted as it implied that even though the wind speed was kept constant around the environment (for example fans and air conditioner turned off), the movements generated by man or usage of balance had minor effect on the accuracy of the result. The effect of these small errors on the result can be eliminated by carrying out more rounds of the experiment, or by repeating with different electronic balances.
Further investigation could be done on finding the values of uncertainty of different sizes and grades of conical flasks. By repeating the experiment with different sizes and grades of conical flasks, we can gain understanding in different instruments and the result might be used as reference in future experiments involving conical flasks.