H+ + OH- H2O It is the making of water, which gives out heat.
I believe that if there is an increase in the concentration of the hydrogen ions, there will be an increased chance of collision so new bonds are formed. In turn producing more water molecules and more heat.
The first acid that I will use will be Hydrochloric acid (HCL). This acid only has one hydrogen ion (H+). So this will limit the amount of heat and also neutralisation. Sodium Hydroxide (NaOH) will be the neutralisation agent I shall use. The Sodium hydroxide had Sodium ions (Na+) and hydroxide ions (OH-).
1M HCL + 2M NaOH H2O
H+ + OH- OH- H2O OH-
Due to the remaining Na+ ion it only produces one H2O molecule. So I believe that the only substance, which is limiting the amount of heat being produced, is the H+.
2M HCL + 2M NaOH H2O
H+ H+ + OH- OH- H2O H2O
However if I were to increase the M then I would get full neutralisation, because there are enough H+ ions and Na+ ions to react with each other producing two water molecules.
3M HCL + 2M NaOH H2O
H+ H+ H+ + OH- OH- H2O H2O OH-
Although there is an increase in the M of acid I have used. The amount of water molecules and heat produced still remains the same as the 2M acid. I believe that this is because there are not enough Na+ ions to react with each of the H+ ions. So the amount of heat and neutralisation still remains the same. The HCL is a monobasic acid, because each molecule will give off only one H+ ion.
Another type of acid I will be using will be Sulphuric acid (H2SO4):
H2SO4 + NaOH NaSO4 + H2O
In the Sulphuric acid (H2SO4) there are two hydrogen ions; this is twice the amount of ions in comparison to the HCL. I believe by using 1M of the H2SO4, I will still achieve the same amount of heat as the 2M HCL acid concentrations.
1M H2SO4 + 2M NaOH H2O
H+ H+ + OH- OH- H2O H2O
2M HCL + 2M NaOH H2O
H+ H+ + OH- OH- H2O H2O
The same amount of heat and neutralisation has been made even when using 1M H2SO4, compared to 2M HCL.
I believe that the Sulphuric acid will produce the most amount of heat of neutralisation, because there are two H+ ions available, for each OH- ion, even if it is at a lower concentration compared to the NaOH. Sulphuric acid is a Di basic acid because for each molecule of the aid will give off two H+ ions. Although I believe that the maximum temperature that will be achieved using sulphuric acid will be at 2M. I believe that because there is only two OH- ions available for each sulphuric h+ ion there will be complete neutralisation up until this point.
The final acid I will be using will be Ethanoic acid (H3COOH). This particular type of acid is referred to as an organic acid. It is hard to predict when or indeed if any of the H+ ions will even dissociate from the molecule. Although the molecule is made up of four H+, only one may separate to form a H+ bond of its own. So I believe that it would be hard to predict the heat of neutralisation.
Main Plan
I will be able to achieve all my results by completing a neutralisation experiment. The three acids, which I shall be using, will be:
- Hydrochloric acid HCL.
-
Sulphuric acid H2SO4.
-
Ethanoic acid CH3COOH.
The variable of the procedure when reacting the acid with the alkali will be the concentration of the acid (molar;0. 5, 0.75, 1.0, 1.5, 2.0 & 3.0). I will repeat the experiment using the acids stated the above. N.B. the sodium hydroxide will remain constant in order to investigate the effects of different concentrations.
I will try to limit the effect of the confounding variables in this experiment in order to make it fair test. The factors that I will have to consider are the following:
- The volume of acid and alkali I use (25ml).
- The temperature of the room must remain ambient at 21°c.
- I will be using the same solution container (a polystyrene cup).
- The reaction time must be kept constant for each time the experiment is repeated (10 seconds).
- The same person must be measuring and timing each experiment.
In order to draw fair generalisations from the procedure I will repeat the experiment twice per concentration for each acid. This will allow me to obtain average results, giving more representative results.
I will be using the following apparatus:
- Hydrochloric, Sulphuric and Ethanoic acid.
- Sodium hydroxide (alkali)
- Goggles.
- Measuring cylinder.
- Polystyrene cup
- Glass beaker
- A thermometer.
- A stopwatch.
- A plastic tray.
Below is diagram displaying how the apparatus should be set up
Method
- Set up apparatus above
- Measure 25ml of Sodium hydroxide using a measuring cylinder and pour it into the polystyrene cup (N. b. ensuring goggles are worn and polystyrene cup is on plastic tray)
- Stir the alkali using a thermometer.
- Measure and record the starting temperature.
- Measure 25ml of 0.5M hydrochloric acid using a measuring cylinder then place into a glass beaker.
- Place the glass beaker onto the plastic tray.
- Add the contents of the glass beaker to the Sodium hydroxide in the polystyrene cup.
- Measure and record the maximum temperature using the thermometer already placed in the polystyrene cup.
- Repeat this procedure for all the concentrations (0.5;0. 75; 1.0; 1.5; 2.0 & 3.0 molar) of hydrochloric.
- Repeat steps 1-9 using sulphuric acid and then ethanoic acid.
The following aspects will be considered when conducting the procedure; I will wear goggles in order to provide adequate eye protection in case of splashes. As a general precaution I will carry out the procedure with care avoiding any potential spillages i.e. ensuring any stools and bags are clear of obstruction. It is important to have a clean and organised workspace so the procedure can be carried out effectively. Further more I will be handling a corrosive substance, which is why a plastic tray will be used.
Tables of results
Results obtained when using Hydrochloric Acid
Results obtained when using Sulphuric Acid
Results obtained when using Ethanoic Acid
Analysis
By looking at my results it is clearly evident that as the acid gets more concentrated, the rise in temperature generally would increase. Another trend that has been demonstrated throughout the results is when the concentrations of the acid doubles or trebles. The rise in temperature is reflected as the strength of the acid increases.
For example when I used 0.5M Hydrochloric acid the average temperature rise was 1.5°c. The average temperature increase was treble the amount compared to the concentration of acid. Also when I used 1M Hydrochloric acid the average temperature rise had trebled again to 3°c. This was what I initially predicted that would happen. I predicted that if I were to increase the concentration of acid the average temperature would rise.
Another trend that I had noticed was when I repeated each experiment. I noticed that when each concentration of acid was repeated the average temperature increase was similar.
Another trend that was evident from my graphs and table was that even when I used 1M Hydrochloric acid and 1M Sulphuric acids, the Sulphuric acid released most energy (heat):
1M HCL + 2M NaOH H2O
H+ + OH- OH- H2O + OH-
1M H2SO4 + 2M NaOH H2O
H+ H+ + OH- OH- H2O H2O
I predicted that the Sulphuric acid would release the most amount of heat. In my prediction I also stated the fact that there were two H+ ions available for each Sodium hydroxide ion, and that this would mean more energy would be released due to the water molecules being produced. Also I predicted that I think at 2M the average temperature increase would level off. This is due to there not being enough OH- ion to react with the H+
However when I increase the Sulphuric acid concentration to more than 1.5M the average temperature increase remains constant up until 3M. The reason for this is because the H+ ions that are available in the Sulphuric acid have all reacted with the Sodium Hydroxide ions, leaving no un-reacted bond:
1M H2SO4 + 2M NaOH H2O
H+ H+ + OH OH- H2O H2O
2M H2SO4 + 2M NaOH H2O
H+ H+ H+ H+ + OH- OH- H2O H2O + H+ H+
I can observe my results for the Ethanoic acid. I had originally predicted that would it be difficult to predict the heat of neutralisation with this acid. The reason for being was that the acid was an organic acid. This meant that even though the acid does have
H+ ions, it would be difficult to predict the outcome, because the ions might not even dissociate from the molecule.
From the information that I have obtained from my results, the Ethanoic acid had produced more energy than the Hydrochloric acid. The reason for this is that the Hydrochloric acid at 1M only has one H+ ion; the Ethanoic acid at 1M has four H+ ions:
1M CH3COOH + 2M NaOH H2O
H+ H+ H+ H+ + OH OH- H2O H2O + H+ H+
I concluded that my results generally favour my original prediction and would furthermore support it. However during the course of my analysis I have come to realise that there are odd results, as these ‘anomalies’ do not correspond with the original prediction. The general conclusion that I have drawn from this experiment is; as the concentration of acid increases, there is an increase in potential collision occurring.
Evaluation
I believe that my main plan helped me to carry put my experiment safely and successfully. The method that I used allowed me conduct my experiment efficiently and safely in the classroom. I believe in general my results were accurate, I did not influence my results in anyway as I wanted to conduct a fair experiment. The conditions in which I conducted my experiment in remained the same:
- The room temperature remained ambient at 21°c.
- The volume of acid and alkali I used (25ml).
- I used the same solution container (a polystyrene cup).
- The same person measured and timed each experiment.
- A 0-50°c thermometer was used
- The experiment was repeated twice.
From my preliminary work I found that using a polystyrene cup rather than a glass beaker. The reason for this was that the polystyrene cup was a better insulator; this was needed to minimize the temperature loss before measuring the temperature increase.
I do believe that my results were reliable, although an anomalous result did occur whilst I was using the Ethanoic acid. The general trend for Ethanoic acid was steadily increasing however at 2M it declined by 1°c. I believe in order for this to have happened the particles of the ethanoic acid didn’t dissociate from the molecule. This in turn caused the decline in temperature.
My results showed that the concentration of the hydrochloric acid at 2M and onwards did not follow the general trend that Sulphuric acid used had demonstrated. This trend was that at 2 M and onwards the increasing concentration had no effect or rather no further increases in temperature as full neutralisation had occurred meaning the temperature should of remained constant which is what I had originally predicted. Hydrochloric acid displayed continuous increase despite the concentration exceeding 2 M. It showed a gradual increase and peaked at 9.5°c. This observation contradicted my original prediction, as the number of hydrogen ions within Hydrochloric acid was theoretically equal to the number of sodium ions, and any concentration there after meant the hydrogen ions should have been in excess meaning the amount of energy given off at 2M and onwards should have been constant. As 2M provided enough hydrogen ions to fully neutralise the sodium ions within Sodium hydroxide.
Apart from the ones I have stated, I did not have any other anomalous results. I believe that my results were accurate.
I feel that the conclusion I have drawn from the experiment could be furthermore supported by improved results. The results that I got from the procedure incorporated anomalous results, which question the certainty of my conclusion. A general improvement to the procedure itself would be to repeat the procedure to give more results and there for better averages in order to draw fully supported conclusions.
Further improvements
I believe that I could of improved the accuracy in my experiment my the following:
- Instead of using a measuring cylinder I could of used a burette.
- I could of used a variety of acids higher than 3M.
- As opposed to a 0-50°c thermometer, I could of used a digital thermometer. It works by placing a heat sensitive probe in the solution. The probe is connected to a computer, which then takes an accurate reading of the temperature.
- I could have placed a lid on top on the polystyrene cup reducing the temperature loss.
- I could of used a vacuum flask. The flask would have cavity insulation so the heat cannot escape.
I believe that further improvements could have been made:
- I could of used a variety of acids such as Nitric acid.
- I could of also used a different alkali to see if that made any difference in the temperature increase.
- I could of used different volumes of acids and alkalis.
- I could of investigated in the prevention of heat loss.
- I believe I could of also have used universal indicator. I could measure out 18ml of acid and use universal indicator to see if is was pure acid. Then I could measure and 25ml of alkali and use the universal indicator to see if it is a pure alkali. I believe that even though if I were to use the same volume of acid and alkali, only a certain amount would be needed for complete neutralisation.