Physics lab report
Experimentation on surface tension through Ring method/ tension metric method
Abstract
Surface tension in liquids is an important property that directly and indirectly dictates the usefulness and application of liquids for various purposes. Therefore investigation and analysis of this fluid property are quite essential for decision making. Though there are quite a number of methods to investigate surface tension, however tensiometric is the most commonly used technique due to its simplicity of the experimental setup and precision in measuring thus providing most accurate results this report presents a laboratory experiment conducted to analyze surface tension of pure water and nonyl-phenol ethoxylate solution with experimental findings and observations explicitly explained in the preceding sections.
Introduction
Surface tension is one of the essential properties of fluids and liquids with different fluids displaying a varied surface tension index. This property also dictates the application of a given fluid on a specific function, for example on applications that involve high temperatures such as lubrication fluids need to have high surface tension. Experimentation of fluids to determine surface tension is essential in quality control and the establishment of various products and processes with enhanced performance efficiency. The necessity for surface tension experiment is manifested on the information extracte4d from the findings such as emulsification, wetting, forming, and washability among other processes related to the fluid surface.
There are quite a number of experimental methods and techniques available for measuring and determining the surface tension property of a given fluid. However, the selection of the best testing technique depends on the nature of the liquid under test. This documentation presents an experimental report on the surface tension using the ring method through the use of a tensiometer. The ring method utilizes a platinum ring fixed with well-defined geometry. It is one of the most common techniques used in most physics labs to investigate the surface tension properties of fluids and the reason behind its preference is on its precision, simplicity, and microbalance of test geometries on precision mechanism. The advantages of testing surface tension are that it provides high sensitivity measurements; through the use of tensiometer and torsion dynamometer, it records even very small measurements.
Methods
The essence of this method is that the rings formed through tensiometer are designed to maintain the surface in a non-equilibrium condition throughout the (surface tension) testing period.
The experiment involved two fluids, that is pure water and nonyl-phenol ethoxylate (non-ionic surfactant solution) with 9.5 units of ethoxylation degree in the water at 100 mg/L
Water and nonyl-phenol soluti0on ware put into two containers, 50 ml of water was placed in one container and 50 ml of nonyl-phenol also in another container.
Then the test instrument (tensiometer) used to measure the surface tension in each liquid as illustrate below.
The basis of ring tensiometry relies on pulling a ring out of the fluid samples on the container and recording the weight of the liquid meniscus attached to the instrument.
The ring of the liquid is then moved towards the surface and the container with test fluid is also moved upwards towards the tensiometer. This procedure is important in that it is applied to determine the zero point balance of electronic force. The ring was adjusted to make contact with the liquid surface to impose the buoyancy of the eth tensiometer ring.
The ring was immersed in both liquids (water and nonyl-phenol) and little force applied to ensure that the liquid samples wetted the ring. After immersion, the tensiometer ring was pulled out gently and at a constant speed. The ring pulled out a meniscus and recorded an increase in the force registered.
The procedure was repeated with solutions at different temperatures and outcomes recorded and as discussed in the preceding sections of this report.
Results and observations
The experiment was conducted in a confined laboratory and experimental set up arranged in a standardized manner. Observations were made on each and every step and results recorded as shown in table 1 and 2
| Rate of pulled-through ring During surface tension experimentation (Mm/min) | Surface tension recorded of pure water (mN/m) | Surface tension recorded of Nonyl-Phenol Ethoxylate Solution (mN/m) |
| 15 | 74.52 | 39.42 |
| 10 | 72.46 | 38.27 |
| 7 | 73.53 | 37.03 |
| 4 | 73.75 | 36.31 |
| 2 | 74.04 | 35.74 |
| 1 | 73.45 | 33.26 |
| 0.5 | 72.50 | 32.34 |
It was observed that for both pure water and nonyl-phenol ethoxylate, the surface tension decreases gradually with a decrease in the rate of ring immersion. However pure water recorded higher values of surface tension as compared to the nonyl-phenol ethoxylate solution.
Table 2 Surface tension of water at different temperatures
| Temperatures 0C | Surface tension (mN m^-1) | Temperatures 0C | Surface tension (mN m^-1) |
| 10 | 75.24 | 21 | 72.30 |
| 11 | 75.06 | 22 | 72.23 |
| 12 | 74.93 | 23 | 72.07 |
| 13 | 74.76 | 24 | 71.98 |
| 14 | 74.62 | 25 | 71.78 |
| 15 | 74.35 | 28 | 71.66 |
| 16 | 73. 22 | 29 | 71.53 |
| 17 | 72.98 | 30 | 71.42 |
| 18 | 72.80 | 32 | 71.16 |
| 19 | 72.64 | 34 | 69.85 |
| 20 | 72.55 | 40 | 69.56 |
As illustrated in table 2, it was observed that the surface tension of pure water decreases gradually with an increase in the solution temperature as the experiment was started at 100C and it decreases up to 400C when the experiment was stopped.
Discussion
The ring technique is often used in the test where it is submerged in the liquid and as the ring is pulled out of the test fluid samples. And the measurement of the forces that are needed to detach the fluids on the ring is precociously measured. The force that is for the fluid detachment is related to the surface tension of the fluid. The total force needed to attach the ring denoted as Wtot is equivalent to the weight of the ring Wr. The surface tension is then multiplied by 2 since it acts on the circumferences of the ring both from the inside and outside.
General expression is as
Wtot =Wr + 4π R γ= Wr + 2l γ
Where R- the ring radius, the inner and outer radius is assumed to be the same since the wire is very thin.
The surface tension value of the solutions was tune fined through a correction factor and changed with an error of up to 25%. With expression F {R3/V, R/r}
From the results recorded in table 1 explicitly shows that water has better surface tension as compared to the nonyl-phenol solution thus proves to be of better properties. Table 2 shows that temperature affects surface tension and an increase in temperature reduces the surface tension of the liquid.
References