Titration Evaluation: The Concentration Of A Solution Of Hydrochloric Acid

Titration Evaluation

Today we did a titration in which we had to find the concentration of a solution of hydrochloric acid. Within this experiment we had to use a number of essential scientific skills such as coordination and patience in order for this experiment to be carried out effectively. We had a number of aims which we tried to achieved, however our main aim was to find the concentration of hydrochloric acid. Firstly we had to understand what a titration. ‘A titration is an experimental technique where a solution of a known concentration is used to determine the concentration of an unknown solution’[footnoteRef:1]. Picture used:[footnoteRef:2]. Before starting, we had to make sure that were carrying out the experiment in a safe working environment. The first thing we did was go through the definition of a ‘PPE’ with our teacher. This is basically a risk assessment and just a check to make sure that we are dressed appropriately for the experiment. First and foremost we had to put on our lab coats. This was to ensure that in the case that any chemicals or acids were to spill on us, there was less of a chance that it would get on our clothes. We had to put on eye protection, for the same reason. So that no hazardous liquids were to get in our eyes. Next we had to prep the area around us for the experiment. We made sure that our chairs were tucked in and our coats and jackets were not hanging off of the back of them as this could cause someone to trip over as they are carrying chemicals.

Before starting we had to decide what our hypothesis was going to be. After speaking with the teacher I decided that my hypothesis, as well as everybody else’s, was going to be ‘What is the unknown concentration of hydrochloric acid?’. I set my hypothesis out as a question so that it would be easier for me to answer. I found that by wording my question in this way, it was clear and to the point. Through making my hypothesis I was able to do carry out my experiment effectively and I had a clear understanding of what value I should be looking for during my experiment. ADD WHAT COLOUR YOU EXPECTED IT TO TURN

After figuring out what my aim was, making sure my working area was safe, and coming up with my hypothesis, I began the experiment with my partner. The equipment we used (including items of clothing) was:

• A balance reading to at least two decimal places
• Eye Protection
• Burette
• White Tile
• Pipette (25.0cm3 ) and filler
• Clamp stand, with boss and stamp (for supporting the burette)
• Filter funnel
• Measuring cylinder (100cm3)
• Glass rod
• Dropping pipette
• Volumetric flask and stopper (250cm3)
• Wash bottle containing distilled water
• Two conical flasks
• Glass beaker (250cm3 and 100cm3)
• Glass marker pen
• Weighing boat
• Spatula
• Dropping bottle containing bromophenol blue indicator[footnoteRef:3] [3: PAG2 Acid-base titration, OCR Oxford Cambridge and RSA, v2.3 – June 2017, Page 3, [Book], Accessed on 25 September 2019 ]

Method Used:

Firstly, we laid out all of our equipment on the desk in order of when it would be used so that it was easier to access. I weighed out 2.10g of the sodium hydrogen carbonate on the balance and then I poured out the substance into the 100cm3 beaker. I rinsed the weighing boat with distilled water and I also poured that into the glass beaker. This was to ensure that almost every spec of the sodium hydrogen carbonate was in the beaker. After this I had to mix it together with a glass rod until it was dissolved and I found that I had to keep adding distilled water for it to fully dissolve. When I had decided that it was fully dissolved I rinsed the glass rod into the solution with the sodium hydrogen carbonate. I then out this solution into a 250cm3 volumetric flask, and I rinsed the beaker, the glass rod, and the funnel into the flask, again making sure that I get all of my original solution into the flask. Once all of my solution was in the flask, I filled the volumetric flask with distilled water up to the fill line and put the lid on and thoroughly mixed the solution.

Next I poured some of the solution from my volumetric flask into the 250cm3 beaker and I labelled as ‘Bicarb Solution’. I transferred it into this beaker so that it was be easier to withdraw using the pipette filler. I withdrew 25.0cm3 of the bicarb solution and put it into the conical flask. At this point it was time for the main part of the experiment to begin. I placed the burette on the clamp stand and made sure the tap was off so that when I poured the ac8id in, it did not come out. I put the stand on the chair so that it was below eye level and I poured the hydrochloric acid up to 0, and this was my starting value. I placed my clamp stand on the chair because if it was above eye level, there would have been the possibility that some of the acid could have accidentally been poured into my eyes. I got my white tile and placed it directly below the burette ready for the conical flask with the solution to be placed on top. I then got my conical flask with the solution and indicator in it and placed it underneath the burette ready for the hydrochloric acid to be poured into it. At this point in the experiment, avoid having one person watching the colour change and another turning the tap as there is a high chance that there could be a communication problem and you may over pour/over dilute(?) the solution therefore causing you to have inaccurate results. As a result of this, appoint one person to both watch the colour change and turn the tap as your own coordination would be better and you are more likely to have accurate results. The first titration I did was my test titration and I did this so that I had a good understanding of what I had to do for the real thing. For my real titrations I followed the exact same steps and I was the one to watch the colour change and stop the tap. My beginning colour was blue however at the end of the titration it had turned to a yellow colour, and I had concordant results. I recorder these in a net table so that it would be easy for me to read my values when I needed to refer to them.

Analysis of my Results

When I had all of my results, I started to calculate their concentrations:

Titre – test number

1 / 2 / 3

Start volume in cm3

Final volume in cm3

37.7 / 37.5 / 37.4

I used the value 0.025 because it is the value of the hydrochloric acid in moles. Also, I divided my final volumes by 1000 because they had to be converted into dm3 for the equation to give the correct answer. As you can see above, my last two results are concordant with each other, however my first result is out by 0.20cm3. The reason I had to do the calculations was because I needed to figure out the concentration of the acid. Therefore at this point, my experiment was done and I had figured out the value which was 0.07.