Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Unit 2 assignment 2 - Lab Report on Study of Cooling curves
Essential Chemistry (University of East London)

SATABDI MORSED 25201308 UNIT 2 Assignment 2
STUDY OF COOLING CURVES:
A cooling graphically shows the change in state of substances from liquid to solid
...

To study the cooling curve of paraffin wax
...


Calibration of thermometers:
Equipment:

•
•
•
•
•
•

Boiling hot water
...

Alcohol thermometer
Digital thermometer
...

Beakers

Risk assessment:
•
•
•
•

There was a risk of burns from the boiling hot water
...

In case any burns had occurred during the experiment, the injured person would have splashed
water on the injured part, and also medical attention would have been provided to the parson
...

In case there were any breaks, the tutor in charge was immediately informed in order to prevent the
risk of cuts
...


Method:
Using ice:
1)
2)
3)
4)

A beaker was filled with ice cubes, and then some water was put in the beaker
...

The ice was stirred again, and then thermometers (digital and alcohol) was placed in it
...
This reading was recorded of results, and
the thermometer was offset
...

2) Once it was boiled, the thermometers (digital and alcohol) were both put in the water
...

3) After 3 minutes, the readings on the thermometers were read and recorded on a table of results
...
(0C)
Digital thermometer
...


1
0
...
(0C)
100
100

Analysis:

The two thermometers were very accurate whereby, their freezing point was at OOCand their boiling point
was at 1000C
Equipment:

•
•
•
•
•
•
•

2 Thermometers (alcohol and digital)
...

Boiling tubes
...

Water
...

Stearic acid
...
This was prevented by
wearing lab coats and also taking care while using the Bunsen burner
...

There was also a risk of cuts in case the glass equipment broke, this was prevented by wearing lab
coats and goggles
...

2) The boiling tube was put into a hot water bath
...

3) The boiling tube was taken out of the water
...
As shown in the table of results for paraffin wax and stearic acid
below;

Results for the cooling curve of Paraffin wax:

2

Time (minutes)1

2

Alcohol
thermometer
...

Temperature (0C)
Time (minutes)18

19

20 21

Alcohol thermometer
...

Temperature (0C)

Time (minutes)34

35

Alcohol thermometer
...

Temperature (0C)

Graph showing the cooling curve of paraffin wax:

4

As the time increases, the temperature of the paraffin wax decreases
...
The
roughly horizontal part of the graphs represents the transition phase (time taken for paraffin wax to fully
transform from liquid to solid state), it shows that there is no change in temperature of the paraffin wax
this part can also be referred to as the melting point
...
This was important whereby, the highest temperature of the paraffin wax
was found, which helped in finding the various changes as it was cooling
...
This was useful in that, the change in temperature at every point
was recorded on the table of results which made it easy to accurately draw a cooling curve of the paraffin
wax
...
The recordings were accurate in both thermometers whereby, the
temperature of the stearic acid decreased per minute
...

Graph:

The graph was accurately plotted with the results that were accurately recorded on the table of results that
are talked about above this is seen from the shape of the graph in that
...
In the alcohol thermometer,
it decreased from 690Cto 580Cin 4 minutes whereas, in the digital thermometer, it decreased from 780Cto
580C in 1 minute
...
The temperature in both
thermometers then moderately decreases in that, in the temperature in the alcohol thermometer,
decreases from SSOCto 360Cin 34 minutes, whereas in the digital thermometer, it decreased from 540Cto
300C in 34 minutes
...


Rate of cooling of paraffin wax in the alcohol thermometer:
Liquid state at 4 mins
...


Transition phase at 21 mins
...


R = 740C— 450C/ 21

R = SSOC—360C/ 34min

= 3
...


= 0
...


Rate of cooling of paraffin wax in the digital thermometer:
Liquid state at 4mins
...
250C/min
...

R = 600C— 370C/ 27min

Solid state at 34mins
...
700C/min
...
85 C / min
...
The calculation was
done by using different time points from different regions of the graph
...
A tangent was then
drawn at the meeting point and the gradient of the tangent was found, this is seen in the calculations
above
...
The tangent
and finding its gradient were carried out at different stages and different a time from the graph, as shown
on the graph and calculations above, in order to find out the rate of cooling at the different time points of
the graph
...
This could have led to an incomplete graph that could not be used to
find the rate of cooling at different stages of the cooling curve
...
Recording the temperature of the paraffin wax after
every minute would sometimes not be done due to lack of concentration, this could have led to an
inaccurate cooling curve because some of the temperature points were absent, making the curve to be
irregular
...

Results:
Some temperature readings at different times could have been wrong due to human errors like writing
down wrong numbers, repetition of numbers and also, missing out numbers
...

Graph:
While plotting the graph, some points could have been missed or drawn wrongly, this could have led to an
inaccurate graph leading to a wrong conclusion of the cooling curve
...
Drawing the tangent in order to
find the rate of cooling was tricky in that, the procedures below should have been followed: the tangent
line should only touch one point of the curve, the opposite angles that were formed by the tangent and the
curve should be equal and also, the tangent line should not cross the respective curve
...
Calculating the rate of cooling (gradient) using the tangent drawn could have been
wrong sometimes due to the use of wrong points and also use of wrong numerical signs during the
calculation
...

Table of results for the cooling curve of stearic acid:
Time (minutes) 18 19 20

21

22

23

23 23 23 23

23 22

24 25 26 27 28 29
22

22 22

22 22

22

21 21 21 21 21 20 20 20 20 20 20

20 20

20 20

Time (minutes)

1

2

Digital thermometer
...


22 22

22 22 22

30 31 32 33

Temperature (0C)
Alcohol thermometer
...

Temperature (0C)

3
45 45 44 41 38 35 34 30

28 27

26

25

24

23 23 22 2

Graph showing the cooling curve of stearic acid:

As the time increases, the temperature of the stearic acid rapidly decreases
...
The

roughly horizontal part of the two graphs shows / means that there is no change in temperature of the
stearic acid
...
This was important whereby, the highest temperature of the stearic acid
was found, which helped in finding the various changes during its cooling
...
This was useful in that, the change in temperature at every
point was recorded on the table of results which made it easy to accurately draw a cooling curve of the
paraffin wax
...
The recordings were accurate in both thermometers whereby, the
temperature of the stearic acid decreased per minute
...

Graph:

The graph was accurately plotted with the results that were accurately recorded on the table of results that
was talked about above, this is seen from the shape of the graph in that;
At the beginning of the graph in both the alcohol and digital thermometer, the temperature rapidly
decreased for a long time
...
The temperature then slightly
decreased in both the thermometers for a short time whereby, in the digital thermometer, it decreased
from 700Cto 310Cin 12 minutes whereas in the alcohol thermometer, the temperature decreases from
230C to 210C in 4 minutes
...
The variations above accurately show the
detailed decrease in temperature of stearic acid
...

Rate of cooling of stearic acid in the digital thermometer:
•

Liquid state at 3mins:
75—63
- 4
3

q

•

= 40C/min
...
25 = 3
...

12

Solid state at 24mins:

22— 22
=0
24

-00Cgmin

Rate of cooling of stearic acid in the alcohol thermometer:
Liquid state at 3mins:
R=

50 —44
-2
3

= 20C/min
...
3= 0
...

16
Solid state at 24mins:
R=

20 —20
0
24

= 0 C/min
...
The rate of cooling at the different points was accurately calculated as
seen above in that, this was accurately done by using different time points from different stages of the
graph
...
A tangent was then drawn at the meeting point and the gradient of the tangent was found, this is
seen in the calculations above
...
The tangent of the curve and finding its gradient were carried out at different stages and different
time from the graph, as shown on the graph and calculations above, in order to find out the rate of cooling
at the different time points of the graph
...
This could have led to an incomplete graph that could not be used to find the
rate of cooling at different stages of the cooling curve
...
Recording the temperature of the stearic acid after every
minute would sometimes not be done due to lack of concentration, this could have led to an inaccurate
cooling curve because some of the temperature points were absent, making the curve to be irregular
...
Less stearic
10

acid was used, which could have led to the rapid loss of its temperature, therefore leading to less time of
transition of the acid from its liquid form to its solid form
...


Results:

Some temperature readings at different times could have been wrong due to human errors like writing
down wrong numbers, repetition of numbers and also, missing out numbers
...

Graph:
While plotting the graph, some points could have been missed or drawn wrongly, this could have led to an
inaccurate graph leading to a wrong conclusion of the cooling curve
...
Drawing the tangent in order to
find the rate of cooling was tricky in that, the procedures below should have been followed: the tangent
line should only touch one point of the curve, the opposite angles that were formed by the tangent and the
curve should be equal and also, the tangent line should not cross the respective curve
...
This could have been prevented by precisely following the above procedures
...




---