Undertake heat capacity. After undertaking this process, a cooling

 

Undertake calorimetry to study cooling curves.

 

Introduction:

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

First of all, calorimetry is the
process of measurement of the heat transferred in a science investigation. It
uses a set up called a calorimeter, which is a basic container such as a glass
beaker with a thermometer placed inside used to measure the changes of state,
phase and chemical reactions. The general uses of this include monitoring
endothermic and exothermic reactions or measuring a specific heat capacity. After
undertaking this process, a cooling curve can be created. A cooling curve is a
representation of the changes of phase of matter which is usually displayed in
a line graph. The independent variable is time and the dependent variable is
temperature. During the experiment, the task I was given was to find the best
method to measure the cooling curve of 10g of stearic acid and 10g of paraffin.
This experiment took a considerable length of time to complete, and a key
factor in this was the room temperature which held at 25 degrees Celsius.

Hypothesis:

The temperature should get decrease
as the stearic acid cools down, and it should continue to decrease after the
state has changed.

Method:

1 )Put on a lab coat, and put on a
pair of safety googles to complete  PPE
to ensure safety during the experiment. 
Once prepared, collect a boiling tube from the heat and a stand from the
cupboard so everything is ready.

2) Ensure the thermometers were
correctly calibrated. This can this by placing the first thermometer in a bath
of boiling water to make sure that the boiling temperature on the thermometer
showed to be 100 degrees Celsius. Then place the thermometer in a tub of ice
and cold water to make sure that the freezing temperature was 0 degrees
Celsius.  This was repeated four times to
make sure accurate results were obtained.

3) Draw a table on a piece of paper
so the results can be recorded. After this is done, proceed to set up the
equipment.

4) As soon as the apparatus is set
up, begin the  stop watch and after every
minute, record the temperature on the thermometer into the table

5) Continue this until the
substance was completely frozen, and a completely white solid.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Equipment:

1.       Filter
funnel stand

2.       Test
tube

3.       Thermometer

4.       Hot
bath

5.       Safety
goggles

6.       Stop
watch

7.       Lab
coats

8.       Stearic
acid and paraffin wax

9.       Paper
pen

10.   Graph
paper

 

Results
tables:

1)      Stearic
acid 10g

Time (minutes)

Temperature (degrees
Celsius)

0

65

1

59

2

55

3

54

4

53

5

53

6

53

7

53

8

53

9

52.5

10

52.5

11

52

12

52

13

52

14

52

15

51

16

51

17

51

18

51

19

50.5

20

50

21

50

22

49

23

49

24

48

25

47.5

 

2)      Paraffin
10g

Time ( Minutes)

Temperature ( degrees Celsius)

0

59

1

55

2

55

3

54

4

53

5

53

6

52

7

52

8

52

9

52

10

52

11

52

12

52

13

51

14

51

15

50.5

16

50

17

49

18

48

19

46

20

45

21

42

22

41

23

40

24

39

25

38

 

3)      Calibration of
thermometer

CALABRATION

BOILING ( Degrees
Celsius)

FREEZING( Degrees
Celsius)

1

100

5

2

100

5

3

100

5

4

100

5

 

 

1( Graph of Stearic Acid

A

 

B

 

C

 

D

 

 

 

2) Graph of Paraffin wax

 

A

 

B

 

C

 

D

 

 

 

Graph:

 As my graphs show, the melting point can
clearly be seen as 52 degrees Celsius. I know this because there is a straight
line along that temperature. This shows that energy has been removed from the
substance with no change to the temperature. This is when it changes from a
liquid to a solid. This is because it had reached its melting, or freezing
point.  A phase change occurs when a
matter in one phase turns into a matter in a different phase. This is due to
temperature, or pressure. As the temperature decreased as it was cooling down.
It can be said that the substance lost energy. This resulted in the molecules
moving a lot slower, and the cohesion, which is the attractive force between
them, ends up  pulling the molecules
closer together leaving them in a fixed position. The melting point I had got
compares very closely to theoretical melting point which ranges from 67 degrees
Celsius. A number of errors could have been the reason for the slight
inaccuracy, such as human error, and the environment it Is done in.

The percentage
difference in my melting point in comparison to theoretical results can be
worked out by doing the following:

 

% difference = difference
in melting points  x 100

                             literature melting
point

Therefore, the
percentage difference would be 22.38%.

 

The cooling curve isn’t very smooth for the stearic acid,
as it seems to have more sudden drops in comparison to paraffin, which appears
to be a nice curve. Perhaps this was due to the rate at which the substances
melts, as the particles in each substance tend to act differently and unpredictably,
or simply human or apparatus error. For stearic acid, it seems to be in a
constant decrease with no signs of any rapid decrease, this means that it
remained approximately constant. This is different to paraffin where it can be
observed that up until the 19th minute, it decreases constantly and
steadily, however when it passes this point it begins to rapidly decrease.

 

 

Evaluation

One key factor in
this experiment was the calibration of the thermometer. This is important
because if the thermometers were not as accurate as they could have been, our
results wouldn’t be accurate therefore it would throw off our entire
experiment. Even though I did calibrate them beforehand, I still came across a
few errors.  As you can see in the
calibration table of results, the iced tub of water didn’t seem to reach 0
degrees Celsius. This could be due to a variety of factors. For example, the
iced water could have began to melt before I could calibrate the thermometer,
or because the thermometer was faulty, or the environment in which the iced
water was kept could have heavily affected its temperature.  Another possible reason could be that the
iced water was contaminated, as the water did have a brownish appearance. This
isn’t good because whatever else was in that water was preventing it from
reaching the freezing point of 0 degrees Celsius, which affected our
calibration. To avoid this next time, we should used an insulated tub and use a
cleaner water source. Furthermore, since the iced water was kept out for a
considerable amount of time before I could reach it, I believe this is the
reason the temperature didn’t reach 0 degrees Celsius. In order to avoid this
next time, I should keep the iced water in a controlled environment like an
insulated tub until I am able to calibrate it straight away. The reason why the
boiling water was so successful, was because I had calibrated it straight from
a kettle, hence the reasons why It continually read 100 degrees Celsius.

 

Another important
factor when it comes to thermometers is the type of thermometers used. In the
calibration, Mercury was used to calibrate the boiling water and an alcohol
thermometer was used to calibrate the freezing water. Mercury thermometers are
generally used clinically in hospitals, or for liquid temperature measurements
in schools and scientific investigations. The advantages of a mercury
thermometer is that it responds quickly to the temperature change. This means
that you wouldn’t have to wait very long for a reading, which would be a
positive factor for my investigation as we were measuring the temperature per
minute. Mercury also has a colour to it, which makes the line of temperature
easy to spot which is an advantage as you don’t have to waste time looking for
the line to read.  However, a
disadvantage is that the displays are generally difficult to read. This is a
hindering factor because it could be easy to misread the temperature, leading
to inaccurate results.  On the other hand,
alcohol thermometers are generally used in hospitals, industry and schools and
colleges, and for domestic uses. The advantage of alcohol thermometers is that
it can be used to measure low temperatures more accurately since its freezing
point is -115 degrees Celsius, and it is quite accurate due to its ability to
expand. This is good because it will be able to more accurately read the
changes in temperature when the substance is frozen, however, this wasn’t
needed in our experiment as the lowest temperature that was reached was 28
degrees Celsius.  Alcohol is also less
harmful than Mercury, as Mercury is poisonous .However a disadvantage of
Alcohol thermometers are that they are bad for measuring high temperatures due
to its really low boiling point.

 

Taking all of this
into account, it was decided that alcohol thermometers were the best ones to
use for the experiment.  All in all, they
did work well to an extent. The lines were really hard to read off of, and it
could have been a lot more accurate. Perhaps a better thermometer choice would
have been a data logger. A data logger is a portable measurement instrument
that is able to autonomously record temperature over a defined period of time.
An advantage of a data logger is that the measurements are automatically taken at
the correct time. This is good because unlike a person, it will not forget to
take the temperature at the right time and it will take it accurately. Another
benefit of data loggers is that the measurements are always taken correctly, as
the computers will never make mistakes unlike a computer. Lastly, when using a
data logger, a graph and table can be automatically made using a data logger
software. This is good because it will save us the time and potentially errors
of making our own tables. However, there is a disadvantage of data loggers
which is that they are quite expensive, and perhaps quite unrealistic for
college use.

There are other
factors which come into consideration when evaluating the accuracy of an
experiment. One factor to take into account is the room temperature. The room
temperature throughout the experiment varied. For example, at the beginning the
windows were left opened, then about halfway through they were closed. The door
was opened and closed throughout the experiment as well. This is important
because if the room temperature wasn’t kept at the average of 25 degrees, it
means that it wasn’t constantly monitored therefore we can’t know what affect
this had on the cooling of the substances. Next time, the windows and doors
should be kept shut and have a thermometer in the room to measure the average
temperature a lot more accurately.

 

Another factor to
take into consideration when assessing accuracy is the surface area of the
stearic acid and paraffin wax containers used. Surface area affects the melting
point by a considerable amount, therefore if the boiling tube used for paraffin
wax was different to the boiling tube used for stearic acid it is possible the
two had different surface areas, therefore the experiment wasn’t completely
fair or accurate.

 

In the experiment,
a lid was not used to cover up the top of the boiling tube. It is possible that
this could have caused slight inaccuracies in the experiment due to heat
escaping from the top, or other substances in the air which could have easily
contaminated the experiment since the air isn’t clean. If a lid was to be used,
it would have ensured that nothing contaminated got in, and nothing useful got
out therefore next time the experiment is conducted, for optimum results, a lid
would be beneficial.

Analysis:

As shown by my
graphs and my results table, there a various trends and patterns to be
discussed. For instance, they both appear to begin to drop at around the 52
degrees Celsius mark. This is because this is the melting point of both the
substances. When a substance melts, it goes through a change of state. When
matter changes state, energy is either lost or gained. When the stearic acid
and paraffin wax cooled down, energy was lost. Liquids solids and gases are
determined by their balance of intermolecular forces which keep them together,
and the kinetic energy of the molecules which drive them apart. We can measure
the amount of energy lost by using a thermometer- because temperature is
essentially a measure of the average kinetic energy. To understand the kinetic
theory, the basics of solids and liquids must be understood. In a solid, you
will find closely packed particles which vibrate in a fixed position in a
regular arrangement, and in a liquid you will find closely packed particles
which can move freely, in a random arrangement. So when something freezes or
cools down, so much energy is lost that the particles slow down so much due to
the lack of energy, that the forces of attraction are strong enough to keep the
particles in a solid arrangement. When the new bonds are forming, the heat
energy begins to evolve. When the stearic acid and the paraffin wax were cooled
down, the solidification releases latent heat into the air. Latent heat is
defined as the amount of heat required to turn a solid into a liquid or gas.

The cooling curve
isn’t very smooth for the stearic acid, as it seems to have more sudden drops
in comparison to paraffin, which appears to be a nice curve. Perhaps this was
due to the rate at which the substances melts, as the particles in each
substance tend to act differently and unpredictably, or simply human or
apparatus error. For stearic acid, it seems to be in a constant decrease with
no signs of any rapid decrease, this means that it remained approximately constant.
This is different to paraffin where it can be observed that up until the 19th
minute, it decreases constantly and steadily, however when it passes this point
it begins to rapidly decrease.