Calibrating pH meters

pH, a term commonly used but understood. The term pH simply is the indication the hydrogen ion concentration of a solution. The abbreviation stands for the French words ‘pouvoir hydrog�ne’ which simply means hydrogen power.

pH is one of the most common laboratory measurements because many chemical processes are dependent on pH. In our modern lives, virtually everything we use has been tested for pH at one time: from the tap water we brush our teeth with, the paper we write on, the food we eat, to the medicines we take, at some point a pH measurement was performed. Although everyone is familiar with Litmus paper, the only reliable way to measure pH is using electrodes. These electrodes essentially monitor the changes in potential voltage caused by differing concentration of Hydrogen ions.

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Aim:

Within this experiment I will be using a Ph meter to identify the pH of three unknown substances. Before conducting the experiment we will also be required to calibrate the pH meters for it to read the pH accurately of the unknown chemicals. The purpose of calibrating the pH meter is so the u can be 99%sure the ph mete is giving of an accurate reading as it is known that accuracy is one of them most factors when conducting an experiment. We will make sure the ph meter is calibrated by using a buffer solution to calibrate which has a guaranteed allowance of 0.001 from ph7.The purpose of this experiment is so that we can successfully use and understand pH meters. My aim to receive accurate results and a calibrated pH meter.

Safety

There are many safety issues that arise when dealing with chemicals and laboratory’s that is why when conducting an experiment all safety aspects need to be thought about before carrying out the experiment otherwise someone could occur contamination or a serious injury when conducting the experiment. One of the main parts of the human body when carrying out chemical experiments are they eyes do to the fact they can easily be damaged and are clearly one of the most delicate exposed parts of the human body. To protect these fragile biological sensors a form of protection is crucial. The most common form of eye protection in the laboratory are the goggles. The goggles appear to be very unattractive to many people but and are often interoperated as a burden and not a safety precaution. The goggles are made out of thick plastic which prevents any liquids entering the eye and causing any harm. Many people who wear contact lenses are under the illusion that there contact lenses will perform as eye protection not realising that the contact lenses are creating a risk of chemicals to become trapped between the lenses and they eye and create extensive eye damage. The goggles can also protect the eye from objects being hurled across the laboratory by immature minds or by the smashing of glass which would send pieces flying in all directions. In the case that somebody’s eye/eyes came in to contact with chemicals follow through the procedures of emergency eye was immediately:

* Water/eye solutions should not be directly aimed onto the eyeball, but rather, aimed at the base of the nose. This increases the chance of effectively rinsing the eyes free of chemicals (harsh streams of water may drive particles further into the eyes).

* Eyelids may have to be forcibly opened to attempt eye rinse.

* Flood eyes and eyelids with water/eye solution for a minimum of 15 minutes.

Clothing is also another aspect of laboratory safety it may not seem like it but It plays a vital part in protecting the skin from the harm of chemicals that is why it is advisory to cover as much of the body as possible while dealing with chemicals due to the fact that chemical can be corrosive and cause damage to the skin. The clothing can help by absorbing as much o the chemical as possible leaving hopefully a minor amount of the chemical to react with the skin. Another way of avoiding contact of chemicals with skin is to use instruments in laboratory such as pipits to transfer chemicals and tongues to handle test tubes etc.

Another aspect of safety to consider when dealing with chemicals is diffusion it is a known fact the by inhaling certain chemicals, these chemicals are labelled as toxic chemicals, can cause serious damage with in your body just by inhaling the vapour through the air. One way of preventing this is by closing lids on all chemicals after use by closing the lid you are also preventing spillages so if the container is dropped the chemical remains inside the container.

Within the laboratory there are frequent spillages that’s why it is important to try and prevent spillages and knowing what the effect of a spillage is and what to do about it. When these spillages occur they can be on minor scale or a disastrous scale. This depends whether the chemical is hazardous or not most lab spillages are on a minor scale and can simply be wiped up by using a damp cloth. With hazardous spillages do not attempt the spillage seek someone qualified to attend to the spillage.

Method

When the experiment was carried out the first thing that needed to be attended to was having all the correct equipment and materials at hand. The following equipment and material were gathered:

* Beaker- A beaker made out of glass with measurement markings on the side.

* pH meter- An electronic device used to measure the hydrogen ion concentration in a solution.

* Deionized water- Water that has been deionized.

* Screwdriver- A tool used to turn screws

* Goggles – Plastic goggles designed to protect the eyes

Once the equipment had been gathered it was placed and was set-up in the centre of the table. All the chemical solutions where poured in to individual beakers once this had been done the pH meter had been switched on and activated ready for use. The electrode of the ph meter had been placed in to the buffer solution and had been calibrated by adjusting the screw at the top of the ph meter so it read pH 7. Once the pH from the buffer solution after the pH meter has been calibrated and was rinsed thoroughly with deionised water. After the electrode has been rinsed it was placed in to the 1st unknown solution and the pH reading was recorded. After we had recorded the pH reading we then removed the electrode from the solution and was rinsed thoroughly with deionised water. This process was repeated with the other 2 unknown chemicals.

Results

As every good scientist knows the results are the main aim of the experiment and recording the results is even more important. Below is a table showing my

personal results along with my peers result as we decided to compare our results.

Name

A

B

C

Amy

4.95

8.89

9.55

Joanne

2.44

8.46

9.37

Mayur

2.24

8.16

9.38

Nicola

2.40

8.39

9.34

Richard

2.25

8.48

9.31

Rishaan

2.52

8.54

9.73

Sonia

2.35

7.99

9.33

Average

2.74

8.42

9.43

All averages are correct to 2decimal places (dp)

Evaluation

I will now evaluate my work to date be referring the aim set at the beginning of the assignment and will evaluate and analyse my performance and accomplishment the objectives.

Aim:

Within this experiment I will be using a Ph meter to identify the pH of three unknown substances. Before conducting the experiment we will also be required to calibrate the pH meters for it to read the pH accurately of the unknown chemicals. The purpose of calibrating the pH meter is so the u can be 99%sure the ph mete is giving of an accurate reading as it is known that accuracy is one of them most factors when conducting an experiment. We will make sure the ph meter is calibrated by using a buffer solution to calibrate which has a guaranteed allowance of 0.001 from ph7.The purpose of this experiment is so that we can successfully use and understand pH meters. My aim to receive accurate results and a calibrated pH meter.

Shown above is the initial aim which was stated within the introduction. When I first created this aim I thought I would have an easy journey. As I carried out my experiment, the errors that I encountered were many, to my surprise. However, in the end I successfully carried out the experiment coming out with accurate results.

As I carried out my experiment I encountered many errors. My first error was a malfunction with the ph meter. The problem was that the ph meter would not seem to switch on. To overcome this problem I tried various methods to turn it on. I tried taking the batteries out and putting them back in. this did not seem to have any effect so I tried replacing the batteries but my efforts were all a waste and I had to replace the ph meter. As I continued to set up my experiment I accidentally broke a beaker whilst pouring the buffer solution in to a beaker. The beaker fell and smashed a technician was informed and attended to the issue.

Once I had overcome setting the experiment up I began to conduct it and firstly I was required to calibrate the ph meter. This is done by using a buffer solution which has a guaranteed allowance of 0.001 from ph7. when the electrode is placed into the buffer solution it would give a reading of a figure and by adjusting a screw u can change that figure. So to calibrate it I dipped the electrode onto the buffer solution and adjusted the screw until the meter read ph7 or the closet figure I could get. Within this stage of the experiment I encountered the error of calibrating the ph meter accurately as the slightest movement could adjust the meter extremely. I mover cam this error of precise calibration by turning the screw driver 10 degrees at a time very slowly making sure I went past each figure on the ph meter. From here on I encountered no obstacles or problems due to the fact I thought about potential problems and how to overcome them.

Within this particular experiment at first I couldn’t see any potential errors but after a while I could only think of one. The potential error that I came up with was contamination of the electrode. I though of this error because I was not satisfied with cleaning the electrode with deionized water. So the solution to this problem that I came up with me involved two of my other peers. The solution was that after we had all calibrated our ph meters we use 1 meter for a solution. So we needle up with 3 meters and 3 solutions. So we allocated 1 meter to one solution.

Overall by looking at the problems and potential problems I had I think I have carried out a very accurate experiment. On the other with all the human error I think the accuracy was not as good as it could have been.

I think that the method and the equipment and the materials for this experiment are great for maximum accuracy but they do not eliminate the chance for human error.

Over all out of the whole experiment I enjoyed the theory the most due to the fact that it enhanced me knowledge about preparing accurate chemical solutions and it showed me it just wasn’t a basic skill but a crucial skill which involved a high level of accuracy I also enjoyed conducting the experiment even though I encountered many errors I enjoyed finding a solution to them. I also think that this experiment has challenged me mentally in every academic way. It has also helped me to develop personal thinking strategies.

During this experiment I learnt quote a lot and enhanced my general knowledge of chemicals as a whole and I learnt practical skills of preparing chemical solutions which I will be able to use in the future.

Over all this experiment has been an interesting and an enlightening experience which I have gained many skills and much knowledge even though I had encountered many problems I enjoyed the experiment thoroughly and would gladly repeat it.