The burette is securely placed onto the clamp and the NaOH is poured into the burette using a funnel and making sure that the tap at the bottom is closed. The conical flask containing the HCl and Phenolphthalein is placed on a white tile at the bottom end of the burette.
The tap of the burette is opened to slowly release the NaOH while swirling the conical flask to combine the two acids. The NaOH is steadily added until the solution in the conical flask turns a pale pink colour. If the solution stays the pale pink for up to 20 seconds then it is permanent even if it goes back to being colourless after a while. The pale pink shows that the acid (HCl) was neutralised by the alkalis (NaOH). The burette was then read to see how much NaOH was needed to neutralise the 25ml of HCl.
I am going to do some preliminary tests before hand to prepare me for the real experiments, which will enable me to have a bit more practice on taking the measurements and using the new equipment, which will help me to improve in my investigation.
To make this a fair investigation I am going to carry out the method on each unknown acid of HCl at least 3 times to prevent any unreliable results. By doing this more than once I will be able to produce an average for each result. I will also spot any anomalies in my results to show where I might have gone wrong to improve on my experimentations next time. I am going to take the readings of the liquids to 2 decimal places to again obtain a more accurate and reliable collection of results.
Results
Acid A
Average result: 25.37ml
Acid B
Average result: 23.90ml
Acid C
Average result: 22.77ml
Acid D
Average result: 19.90
Acid E
Average result: 17.37
Averages of the acids
Calculating the concentrations of the acids in moles:
Acid A
0.1M x 25.37 - moles in titre
1000ml
= 2.537 x 10 x 1000
25
=0.10 2.d.p
Step by step of the calculations above
There is 0.1M in a 1000ml and so in 1ml of the NaOH there are 0.1 moles,
1000
we can then find out how many moles of NaOH we used. It is then multiplied by 25.37 which is the amount of NaOH that was used and is also divided by 25 because that is how much of the HCl that was used every time. The whole sum is then multiplies by 1000 to show the amount of moles in 1000ml of the NaOH which is needed to neutralise the acid.
The number of moles in the NaOH is also the same as the HCl because I know from the equation below that they have a one to one relationship, which means for every 1M of NaOH, there is 1M of HCl.
HCl + NaOH ---------- NaCl + H20
Acid + alkalis ---------- salt + water
Final results
Evaluation
The results of the investigation did not exactly meet my prediction of the HCl concentrations being less than 0.1M because it had been topped up with water, weakening its concentration. This is because the HCl had a higher concentration than 0.1M to start with, which could have been the fault of the technician who topped up the Winchesters.
I do believe that my sets of results are very reliable considering that they were all tested fairly and carries out several times to produce a better, more accurate set of results. The 3 results of each concentration of the acids were also very close to each other which shows that each time the test was carried out they were performed accurately with only a slight difference to each other. There are no major anomalies in my results which may also show that all the tests were done carefully and each one was successful and reliable.
On each time the experiment was performed, the end point at which the acid was neutralised by the alkalis was always carefully done without pouring too much of the NaOH into the flask which could have made it alkalis and turn the colour a deep pink. The easiest way I found to be able to reach that point is before the acid was about to be neutralised, small drops of the NaOH was added slowly until it turned pale pink and stayed for at least 20 seconds. I did not have any difficulty in reaching the end point and managed to create a pale pink coloured solution each time.
I didn’t find any major problems apart from the pipette fillers which would sometimes make air bubbles in the pipettes as it was measuring and taking the HCl.
The investigation can be improved by taking further results of each concentration of the HCl to produce an even more accurate and reliable source of results. Better equipment can also be used and different kinds of equipment to see if they give accurate readings to 2 decimal places.
