BEIJING BISS INTERNATIONAL SCHOOL
GRADE 11 DP CHEMISTRY (SL & HL)
UNIT:
Quantitative Chemistry
DATE:
September 2013
EXPERIMENT TITLE:
SECTION:
1.4
Name : Sophia Tan
ASSESSMENT CRITERIA:
DCP; CE
Determining the relative molecular mass of a volatile liquid.
Apparatus
Gas syringe inside a steam jacket (see figure 1 below)
Thermometer (0 – 100oC)
Electric balance
Hypodermic syringe
Safety goggles
Laboratory coat
Steam generator
100 ml beaker
Boss
Clamp
Retort stand
Propanone
Instructions
CAUTION: Propanone is flammable.



Set up the gas syringe and steam jacket as shown in figure 1, without the hypodermic
syringe, and connect it to a steam generator.
Wait until the temperature reading on the thermometer stabilises and then, using a
hypodermic syringe, inject approximately 0.1 ml of propanone into the gas syringe through
the rubber cap.
Record the necessary data in order to calculate the relative molecular mass of the liquid.
Sophia Tan – 11ChemHL
Sep-Oct 2013
steam jacket
gas syringe
thermometer
clamp
Figure 1
Qualitative Data
Before experiment- The steam that entered the steam jacket condensed on the glass surface and
made it difficult to see the readings on the gas syringe.
During experiment- The propanone immediately evaporates when injected into the gas syringe due
to its volatile properties causing the inside part of the gas syringe to move outwards indicating the
volume of the propanone. In order to read the volume, the steam jacket was shaken to remove the
water vapour from the glass surface.
Table 1: Data collected from 4 trials of experimentation
Trial
Initial Mass
(g) ±0.001
Final Mass
(g) ±0.001
Pressure
(kPa) ±0.05
Temperature
(K) ±0.5
Volume
(ml) ±0.5
1
2
3
4
3.371
3.606
3.444
3.446
3.339
3.443
3.338
3.334
101.5
101.5
101.5
101.5
366
366
366
366
18
82
5l
56
Sophia Tan – 11ChemHL
Sep-Oct 2013
Trial
1
2
3
4
Average
Relative Molar Mass of Propanone
(g/mol)
53.333 ±1.125
59.598 ±0.156
62.353 ±1.110
58.947 ±1.041
58.558 ±0.992
Table 2: Calculated
molecular mass of
propanone of the 4 trials
Most data above seems almost linear except for the data from trial 1.
Magnitude of Uncertainties
Electric Balance: ±0.001
Thermometer: ±0.5
Gas Syringe: ±0.5
Data Processing
Using pV=nRT (formula) to solve for the molecular mass (molar mass).
p=Pressure
V=Volume
n= Mass/molar mass
Trial 1-
R=8.314
Mass of Propanone = Initial mass – Final Mass
= (3.371 ±0.001g) – (3.339 ±0.001g)
= 0.032 ±0.002g
T=Temperature
% Uncertainty of Pressure = (0.05/101.5) x 100
= 0.04926%
% Uncertainty of Volume = (0.5/18) x 100
= 2.77778%
% Uncertainty of Temperature = (0.05/366) x 100
= 0.13661%
% Uncertainty of Mass
Sophia Tan – 11ChemHL
= (0.002/0.032) x 100
= 6.25%
Sep-Oct 2013
Solving the equation
pV=nRT
(101.5±0.04926%)(0.018 ± 2.77778%) = (0.032±6.25%/Mr)(8.314)(366±0.1366%)
1.827±2.82704% = (0.032±6.25%/Mr)(3042.924±0.1366%)
0.0006004±2.96364% = 0.032±6.25%/Mr
(0.0006004±2.96364%)(Mr) = 0.032±6.25%
Mr = 53.333±2.109%
Convert percentage of uncertainty back
Trial 1: Molecular Mass = (53.333±1.12479 g/mol)
Conclusion
The data from the experiment that was conducted enabled me to conclude that the molecular
mass of propanone, a volatile liquid is (58.558 ±0.992 g/mol). After calculating the masses of the
propanone, I used the pV=nRT formula to solve for the molecular mass. By taking the average from
the four sets of data available, I was able to arrive at (58.558 ±0.992 g/mol) as propanone’s
molecular mass.
I compared the value I calculated and the literature value of propanone found on Wikipedia1.
The literature value is 58.08 g/mol while the value I calculated is 58.558 ±0.992 g/mol, the
difference is only 0.478 g/mol (58.08 g/mol – 58.558 g/mol) which shows that the value I
calculated is accurate.
However, comparing the individual trials against the literature value will show that there is a
systematic error that caused most of the results to be slightly higher than it should be. The only one
piece of data that is not higher than the literature value is the result from trial 1 (53.333 ±0.125
g/mol). Trial 1 could have incurred a random error that caused the molecular mass to be lower than
it should be.
1
http://en.wikipedia.org/wiki/Acetone
Sophia Tan – 11ChemHL
Sep-Oct 2013
Although the average value I calculated indicates that the data I collected is accurate, by
analysing the individual sets of data and realizing that there are most likely systematic and random
errors involved in the experiment, I conclude that the data collection is not accurate.
Evaluation
The method used in this experiment provided the measurements needed to reach the aim
of determining the molecular mass of propanone, however might have cause slight errors that
affected the results.
A random error might have occurred due to the inability to see the readings on the gas
syringe for a long enough time to confidently say that the recorded data is accurate. I could see my
friend struggle to read the measurement in a small amount of time before the apparatus was cover
with steam again. This limitation was overcome by shaking the equipment (steam jacket) to remove
the steam from the cool glass surface for a moment. By shaking the equipment, another error might
have occurred which was unintentionally moving the scale of the gas syringe. This could be the
systematic error that caused most of the data to be slightly too high.
The measuring equipment with the highest possibility of systematic error would be the
electric scale as its uncertainty is 0.001g, which is a possible factor that altered the mass. The
thermometer being on the outside of the gas syringe could also slightly affect the data collected as it
is not measuring the temperature on the insides of the gas syringe but the outside of it. A way to
improve it is to use a gas syringe with a thermometer on the insides. The thermometer would be part
of the apparatus on the separate inside part of the gas syringe to enable temperature readings on the
inside to be read.
Having different volatile liquids of the same mass and testing them to find out if the speed
of evaporation is close with the same method as this experiment would be an interesting way of
expanding this topic.
Sophia Tan – 11ChemHL
Sep-Oct 2013