Therefore: Moles of NaOH= Moles of HCl
Gastric Juice is found in the stomach and is extremely acidic with a pH of around 1.0. Therefore as it is a strong acid, it will be good to titrate against NaOH that is a strong base.
The equipment involved in a titration is a Burette, Volumetric pipette and a Conical flask. The Burette is used to measure accurately the volume of a solution added. Reading can usually be read to an accuracy of +0.05. A 25cm3 pipette is used to accurately measure a standard volume. Lastly I will be using a Conical Flask which will contain the 25cm3 of either HCl or Gastric Juice.
[1] Figure 1: Equipment set up for a titration
Experimentation
- Take the burette out of the clamp and place a funnel at the top.
- Pour the given NaOH into the burette through the funnel until the meniscus is at 0 at eye level.
- Place the inverted burette back into the clamp making sure that the tap is fully shut.
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Attach the 25cm3 pipette to the pipette filler
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Using the 25cm3 pipette, measure 25cm3 of either HCl or Gastric Juice.
- Once measured, release the content of the pipette into a conical flask.
- Add 2drops of the indicator, Phenolphthalein to the flask.
- Place the conical flask on top of the white tile and directly beneath the inverted burette.
- Open the tap and slowly let the NaOH slowly release into the conical flask until you notice a colour change and then close the tap so only a few drops at a time fall through.
- Stop until you get your end point, in this case the end point should be pink.
- Note down your results.
- Repeat the experiment 3 times
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In order to get concordant results, results should be within +0.01 of each other.
- Repeat the experiment using gastric juice as your standard instead of HCl.
Results
Results showing the titration of sodium hydroxide solution with 25cm3 0.01mol dm-3 HCl:
Average Volume of Sodium Hydroxide solution used= 25.60cm3
Number of moles of NaOH present in this volume
= 2.56 x 10cm-4
25.6/1000
=25.6/1000
Therefore: molar concentration of NaOH= 0.01
Results showing the titration of sodium hydroxide solution with 25cm3 0.01mol dm-3 Gastric Juice:
Average Volume of Sodium Hydroxide solution used= 30.8cm3
Number of moles of NaOH present in this volume:
=3.08x10-4
30.8/1000
=30.8 x 10-4
Therefore number of moles of HCl in 25cm3 of gastric Juice= 3.08 x 10-4 moles
Therefore: molar concentration of HCl in Gastric Juice= 0.01 mol dm-3
The measured pH value of the gastric juice = 2.2
Discussion
The results I obtained showed me that they are reliable and accurate as for both titrations, HCl and Gastric Juice all the titrations are within 0.10 of each other. In the first experiment, the titration with HCl, I did not have to Do a third titration as it was not needed. This was because the three results I obtained including the rough titration was all between 0.10 of each other. However for the second the second experiment , a third titration was needed as I had a anomaly as it was not between 0.10 of each other. The average of Sodium Hydroxide was used in the the first experiment was, 25.6cm3, and in the second experiment it was 30.8cm3. I obtained by average volumes by adding the three volumes together and dividint it by 3. As we know the number of moles of NaOH was the same as the number of moles of HCL as it was in a 1:1 ratio, therefore the moles were the same. In order to get the molar concentration, I used the calculation:- Moles/(Volume/1000). I had to divide the volume by 100 as I had to convert it to dm-3.
During my titration, determining what the end-point was could be argued to be one of my main procedural errors as there is nothing to measure against except for my own personal judgement in determines the end-point. In order to overcome this experimental error and its subjectiveness, I could use a colour chart which already has the colour of what the expected endpoint should be. The chart could have a scale which will give you a better indication as you can compare the colours.
Now looking at the observational errors which I came across was firstly, taking readings off the burette which may have been out by a couple of decimals. In order to make this more accurate, I could use longer and thinner burettes which will allow me to obtain a much more accurate reading. Also the pH of gastric juice differed. In order to overcome this, we could measure the gastric juice beforehand instead of after the experiment. We could also measure it before each titration.
In my experiment, I tried to minimise error wherever I could and also make my experiment reliable. I tried to make sure, in order to minimise any possible additional errors to wash out all of my equipment by washing it with distilled water to avoid any contamination. All of my experiment I would say is reliable as they can be repeated and tested again.
Conclusion
In conclusion, my results were accurate and reliable to the best of my ability; however with using more precise equipment and having a longer to do it may have increased the accuracy. Also with aids of a colour wheel in order to obtain the same shade of pink may help. The aims of this experiment were met was we managed to work of the molarity of our two substances by using the titration method. Overall I think that the titration experiments for both the HCL and the gastric juice were successful.
Referencing
