Reference no: EM132238375

Determination of the Effect of Various Dissolved Chemicals on the Surface Tension of Water

The aim of this experiment is to give you some experience of preparing suitable solutions of a number of common chemicals and performing a simple experimental procedure that compares the effect of both the chemical and its concentration on the resulting surface tension of the solution.

Learning Outcomes

By performing this practical, you will have experience of:-

• preparing simple solutions of common household chemicals with different chemical and physical characteristics
• using a simple experimental procedure to determine the relative effects of both the chemical's identity and the chemical's concentration on the resulting surface tension of its aqueous solutions
• recording procedures, observations and results in a clear form
• assessing the reliability and reproducibility of your observations, and any differences that may arise using simple statistical analyses
• evaluating the overall validity and significance of your results
• presenting your results in a suitable scientific report and drawing conclusions, supported by suitable literature references, and including a critical evaluation of the data and experimental findings
Materials
You will need to assemble some ‘simple materials and items of equipment' from around the home:
• Some small containers e.g. some small plastic cups (obtainable from most supermarkets)
• A marker pen
• A ‘one penny' coin (or similar coin in any currency, material is not important)
• A box of tissues or kitchen roll
• Some table salt - sodium chloride
• Some ordinary sugar - sucrose
• Some ‘washing up liquid'
• About 500 ml of de-ionised water (as used to ‘top up' old car batteries or as used in some steam irons)
• A small cooking measure e.g. a quarter of a teaspoon (about 1.2 ml)
• A larger capacity cooking measure e.g. an eighth of a cup (about 30 ml)
• 1 ml plastic syringe with appropriate gradations on the scale (to be sent by mail)

Experiment
1. Make up a series of solutions in your plastic cups as follows :-
1. Take five cups and number each cup (1-5) using a marker pen.

2. To the appropriately numbered cup, add the following components according to the table below (Table R1.2).

3. Swirl and mix the contents of each cup (2-5) to ensure all the salt is dissolved fully.

2. Take a ‘1 penny coin' and clean it with some tissue and water, and then place the coin on a level surface e.g. a kitchen work top.

3. Fill the 1 ml syringe with some of the contents of cup 1 (distilled/deionised water) to the 1 ml graduation accurately. Then gently and slowly dispense/drop the water onto the centre of the coin, from a height of about 5 - 10 mm above the coin. The liquid will accumulate on the coin's surface and form a ‘droplet' that will eventually cover the coin's entire surface and then ‘build up' on the surface of the coin. Always maintain a small gap between the outlet of the syringe and the liquid/droplet accumulating on top of the coin.
4. Continue slowly adding more liquid to the droplet on top of the coin. You may find that you need to refill your 1 ml syringe with more water, so you should make a note of the number of times that you have refilled your 1 ml syringe.

5. Continue slowly adding more liquid to the droplet on top of the coin until, on the addition of 1 drop, the accumulated liquid on top of the coin ‘overflows' onto your kitchen work top.

6. Note the total volume of liquid needed to cause the accumulated liquid on the coin to overflow, as accurately as you can (e.g. 1.45 ml).

7. Absorb the dispensed liquid (now mainly on your kitchen work top) into tissue or kitchen roll and dry the coin with tissue / kitchen roll. Repeat the experiment for a total of five times and note the volume of water used in each ‘run' of the experiment. Measurements performed with the contents of cup 1 constitute the control part of the experiment.

8. Repeat the experimental procedure (points 2 to 7 above) with each of the other salt solutions in cups 2 to 5. That is you will make 5 measurements for each of the 5 cups 1-5.

9. For the groups of measurements for each solution (cup), average (mean) the volumes needed in each case and calculate the standard deviation and the standard error on the mean.

10. Perform an Unpaired t-test (see later) on your data to see if the addition of various amounts of salt significantly alters the surface tension of water at both the 1 % and 5 % levels.

You can then perform further experiments following the same procedure (1 to 10 above) using other chemicals dissolved in the 30 ml of water in each cup. For example, you could repeat the above experiment substituting the salt with sugar (sucrose) or washing up liquid. Washing up liquid may be a little more difficult as the viscosity of the washing up liquid complicates the accurate addition of each amount to the solution (¼ teaspoon or about 1.2 ml). Ensure that each addition of washing

up liquid is fully dispersed and dissolved in the appropriate cup by gently stirring the water (avoid excessive foam formation) in each case by gently stirring the cup's contents with the ¼ teaspoon measure, until all the washing up liquid has dispersed into the water in that cup. Then wipe and dry the ¼ teaspoon measure with tissue and repeat the addition procedure as necessary. Also if you are reusing your cups, then see the notes below.

You can also combine additions - for example mixing certain amounts of washing up liquid with salt or sugar (or both) and noting the effect on the resulting estimate of surface tension.

In all cases, it is important to note exactly what you have done in your experiments, by recording the results of your experiments in a notebook.

Surface Tension Experiment - writing the report
After carrying out the experimental part of the experiment, you are now expected to analyse and evaluate the results that you have collected. The work should include summary tables of data and results, appropriate diagrams and graphs, and be structured in line with the "General Experiment Brief" (on Blackboard).

1. Introduction/Data Collection and Accuracy

Write a short introduction explaining briefly what the experiment is about and its aims.

Describe (in your own words) your experimental method/procedure, especially where it differs from the script.

For each solute (salt, sucrose, washing up liquid), you will have measured the effect of the addition of these solutes on the resulting surface tension of the solution under investigation, from the maximum volumes of solutions that will form 'a drop' on top of the coin, compared with similar measurements with pure water. These measurements will be replicated. Tabulate your raw measurements.

Calculate the mean and standard deviation of your measurements. These give a measure of the precision and reproducibility of your experimental technique and measurements. Discuss why the variations you see have occurred.

2. Data Presentation and Analysis
Calculate the standard error on the mean for each set of data. Then perform an
'Unpaired t-test' on your data to see if the addition of a solute significantly alters the surface tension of water at both the 1 % and 5 % levels. For details of how to perform a 'Unpaired t-test', see separate file Data Analysis Briefing for Report 1.

Graphically represent some of your data by plotting the effect of the amount of solute (volume of solute / 30 ml - in effect its concentration) on the resulting solution's surface tension (using the maximum volume that can be accommodated in a drop on top of the coin as a proxy measurement).

3. Discussion, conclusions and bibliography

4. Analyse your data in greater depth and evaluate the 'quality' of the data collected. The following questions will help you focus the discussion.

1. What effect(s) are the solutes having on the surface tension of water?

2. Are your findings consistent and reproducible?

3. Can you explain the scientific basis for any effects observed?

4. Are there alternative explanations?

5. Does the chemical nature of the solute matter?

6. Do your results agree with the same or similar measurements that you might find in the literature?

7. Are there any sources of inaccuracy or potential flaws in the methodology used? Can you suggest modifications to the experimental protocol in the light of your evaluations?

8. Link your work to the concepts introduced in the introductory passage of this experimental brief. Think about how the results might have relevance to the initial formation of life, and reflect on how they relate to the module materials in Sections 1 to 6. ie discuss the experiment in the context of Astrobiology.

Where possible your evaluations should be backed up by appropriate references of the literature and the reference sources should be cited in full.

Word count:2000

Attachment:- Report.rar