Suitability Test

Sensitivity

Durability

Easy To Use

Out of all of the methods, the cheapest is the Litmus paper.   But, the litmus paper has the worst accuracy.  The most accurate is the pH probe, but it is by far the most expensive piece of equipment.  The quickest method was the Soil probe.  It took about 1 minute per experiment.  The longest test to do was the pH probe.  It took about 10 minutes.  Both the U.I. solution and the pH probe are has the best sensitivity.  The pH probe is more accurate, as it finds the result to two decimal places, but the U.I. solution is second most accurate as it goes to 0.5.  

Method 1 – Litmus Paper

I measured out soil into each flask, and added two spatulas of Barium Sulphate.  I then added 80ml of distilled water into the conical flask.  I then put the bung and shake.  The flask was left to settle for five minutes.  Using a pipette fill 5 dimples in the dimple tray.  Dip a piece of red and blue litmus paper into each dimple and watch for any colour changes.

It was quite easy to do, but it was difficult to get equal amounts of soil by using a spatula, so it would be much more accurate if the soil was weighed out using something like scales or the pan balance.  

Method 2 – Universal Indicator Solution

I put one large spatula of soil into the conical flask.  I did one for Soil Sample A, one for B and one for C.  I then added 2 spatulas of Barium Sulphate to the conical flasks.  Next I added 80ml of distilled water to the flasks and placed the bung in the top.  I shook the conical flasks, and left it to settle for 5 minutes.  Using a pipette, I put approximately 1cm3 of the solution into each of the test tubes.  To analyse, I compared the colour with the pH chart and recorded all the results in the table.

There are two ways I can think of to improve, the first way would be to use something more accurate than a spatula, and secondly there should be a better and more accurate way to measure out 1cm3 of the distilled water.  A small measuring cylinder would do the job, or again you could use scales or the pan balance.        

Method 3 – Soil Probe

For this method, I put 50ml of the soil samples into the 50ml measuring cylinders.  Next, I used the 10ml measuring cylinder to measure out 5ml of distilled water.  Next I poured the water into the soil, and then waited for the water to soak into the samples.  I needed to calibrate the soil probe before each test.  This was done by dipping the end in distilled water in the conical flask.  Before taking readings, it needed to be dried.  To take the reading, I put the probe in the soil, and took a reading after 60 seconds.  I then removed the soil probe, wiped it clean and did 4 more readings.  

It was a very lengthy process doing this one, as I had to clean it well after each reading, making this method not the quickest!  A more accurate way again would be to use the Pan Balance to measure the soil samples out.  

Method 4 – pH Probe

To do this method, I put a large spatula of each soil into the conical flasks.   Next I added 80ml of distilled water to each of the conical flasks.  I then put a bung in the top and shook it.  Next I needed to filter the water and soil.  To do this I put a piece of folded filter paper into a funnel and put the funnel above a glass.  I poured the soil solution into the funnel and left it to drain into the glass.  When it was all drained into the glass, I evenly spread the mixture among five boiling tubes.  I was then ready to take the readings, but first the pH Probe needed calibrating.  To do this, I submerged the end in pH7 buffer solution in the glass beaker.  The probe should have a reading of pH7.  I then rinsed it in distilled water before finally putting it in the first boiling tube and taking a reading.   It then needed a rinse and clean.

This was definitely the most confusing method of them all, and also the longest, and most expensive!  It was very accurate but it’s not Worthwhile using this method.

If I was to choose a method I would choose the 2nd Method, the Universal Indicator solution as it is accurate and the most simple of the lot!