The pendant drop method for determination of surface and interfacial tension has been known for several decades
science
Description
1) The
pendant drop method for determination of surface and interfacial tension has
been known for several decades and has become popular relatively recently. Using any diagrams and equations you think
are necessary, outline;
I.
The principles of this
method, from both experimental and theoretical perspectives, referencing all
your sources.
II.
State the advantages and
disadvantages that the technique has in comparison to other methods (eg De Noüy
ring or Wilhelmy plate methods) and.
III.
Suggest why the method has
become commonplace only in recent years.
(200 words
Maximum)
(20 marks)
2) Use
the data
in the table below to;
a. Calculate
the dispersion and polar (hydrogen bonding) components of the surface tension
of water. Explain your approach and why.
(10 marks)
b. Making
use of the above result and any relevant data from the table, calculate:
I.
The interfacial tension of
octanol on water.
II.
Justify any approximations
or assumptions you have made.
(15 marks)
3) Determine:
a. whether
octanol will wet the surface of the polymer (PY).
b. Explain
your theoretical approach and outline any assumptions you have made. (18 marks)
Data for
questions 2) and 3) from pendant drop measurements
|
Species |
/ mNm-1 |
Interfacial
tension on water / mNm-1 |
Surface
contest angle on (PY) |
|
Water |
72.8 |
- |
113.7° |
|
Hexane |
18.4 |
- |
12.0° |
|
Octane |
21.3 |
46.3 |
- |
|
Octanol |
27.5 |
- |
- |
4) The
initial spreading coefficient of octanol on water has been measured as
36.8 mNm-1. From this
determine:
a. The
octanol/water interfacial tension.
b. Compare
this with your calculated value from question 2) and
c. suggest
reasons for the discrepancy between the two values.
(7 marks)
Instructions
a)
Show all working clearly
b)
Explain and justify your approach (eg
calculation method or principles used to solve the problem) and this must be
written in clear and unambiguous English.
c)
Aim your explanations at a scientifically
literate person who is a non-expert in this topic.
d)
Diagrams should may be used to enhance your
answers, and should may be neatly hand drawn and scanned in to the word
document. (not photographed please)
e)
You will need to reference each answer that
has been explained.
f)
Number of references should be At least 5
|
Question |
Assessment Criteria |
Mark |
|
1 |
Correct theoretical explanation and outline
of experimental setup |
15 |
|
1 |
Clarity of answer, including use of
diagram(s) and relevant references |
5 |
|
2a |
Validity & clarity of approach, with
correct calculated values |
10 |
|
2b |
Validity & clarity of approach, with
correct calculated values |
12 |
|
2b |
Discussion of assumptions |
3 |
|
3 |
Validity & clarity of approach, with
correct calculated values |
15 |
|
3 |
Discussion of approach to solving the problem |
3 |
|
4 |
Determination of interfacial tension |
3 |
|
4 |
Reasoned discussion of discrepancy with value
from question 2b. |
4 |
|
|
|
|
