Safety
In this experiment, you have to take safety pre-cautions, the are:
- Wear safety goggles
- Don’t keep the apparatus near to the edge of the table
- Be careful not to split any acid or anything else if this happens then call a teacher
- Clean the apparatus so the next person that uses it won’t get acid on them.
Prediction
Before I have done the experiment, I have predicted that the sodium hydroxide will neutralise when about 25cm of acid is put in. The reason I think this is because the ratio of the reaction is 1:1 so each sodium hydroxide particle joins together with each of the hydrochloric acid particle so this cancels them out to make it neutral. The particles in the sodium hydroxide are reaction in the ratio 1:1 this means that for each sodium hydroxide particle there is a reaction accruing with a hydrochloric acid particle. When neutralising I think that the temperature of the sodium hydroxide will increase because the reaction is an exothermic reaction, this means that heat is given out. In the experiment, the sodium joins the chlorine to make sodium chloride (NaCl) and the hydrogen joins with hydroxide to form water (H2O). I think that the more acid I add the more heat will be realised. The formula for this experiment is:
Sodium hydroxide + hydrochloric acid sodium chloride + water
This equation should be balanced in order for neutralisation to occur, the balanced equation for the experiment is:
NaOH + HCl NaCl + H2O
Result table: First experiment
There were seven drops of universal indicator added in the sodium hydroxide.
Result table: Second experiment
In this experiment, there was also seven drops of universal indicator used.
Analysis
When I done the experiment my prediction was correct to the results. I found out that the temperature does rise as you add more acid. The alkali neutralised at about 26.8 or 26.9, this shows me that you need about the equal amount of acid to neutralise the sodium hydroxide. When the neutralisation process was done I noticed that the temperature if the solution had decreased. As you can see on the graph the curve of best fit went straight up in the beginning then settled and after the 26.8 mark the curve went down. Some factors that could have affected the results could have been was when I was doing the experiment I was near a open window so the temperature could have decreased because of the wind coming in. I think the temperature of the solution also decreases after neutralisation because the solution in the cup was hot, the alkali has all been used up, and adding acid to it is like adding cold water to hot water, which makes the temperature decrease. As you can see on the graph, the temperature started to set at about 32.2°C – 32.5°C.
Evaluation
Once I had done the experiment and achieved my results, I felt that my results were quite accurate. Some ways I could have improved my results is I could have added less acid each time another way I could have improved my experiment was by moving my experiment away from the window so that the temperature would be more accurate. Whilst doing the first experiment the colour (purple) at the beginning was the same from the starting point to about 22.5cm, and then changed to navy blue. When we were reading the burette, it was quite difficult to get the exact point. When we did the experiment, the temperature was different to the day we had done the second experiment so this might have affected the temperature of the solution in the cup. Whilst I was plotting the graph, I noticed that there were some anomalies (points that are left out of the curve of best fit). the reason I think there were some anomalies is because as I said before I was doing the experiment next to a window which could have affected the temperature of the solution causing inaccuracy in the results. You can see this on the graph and the point which were not included I have circled. I had done this experiment 3 times because the first time I had done it I kept adding too much acid so the results were incorrect, but the other two experiments I did more correctly and put less acid each time. In the first experiment, I used a 100cm measuring cylinder that didn’t help me to get exactly 25cm of alkali, but in the second experiment, I then used a 25cm measuring cylinder that gave me a more accurate reading. In the end of the experiment, I found out that to neutralise the alkali you needed to add about the same amount of acid. I also found out that the temperature increases when I was neutralising the alkali and the temperature decreased when the alkali was already neutralised.
