The heat increase was 12.5ºC. When looking at the graph the delta T value is 12.5ºC. This value when substituted into the formula
ΔHr = m x 4.2 x ΔT
Should give results approximate to 58000Jmol.
= 50 x 4.2 x 12.5
= 2625J
However, this is when 0.05 moles of acid reacts with 0.05 moles of alkali. To find out for 1 mole we must multiply from 0.05 to 1. To do this we multiply by 20.
1 mole = 2625 x 20
= 52500Jmol
This result shows that the degree of accuracy is quite high.
Equipment
Safety glasses
Pipette filler
Pipette 25 cm³
Polystyrene cup with lid
Beakers
Sulphuric acid 75 cm³
Potassium Hydroxide 125 cm³
Stopwatch
Thermometer 0ºC-50ºC, 0.1ºC gradients
Burette
Water
Prediction
I predict hat the higher the concentrations the greater the value of ΔT and in turn the value of ΔHr. I base this prediction on the my scientific knowledge about concentrations in reactions. The more particles there are the more chance of collisions, and the more collisions the greater the chance of successful collisions.
Method
Set up equipment as shown in the diagram.
- Put on the safety glasses.
- Pour KOH into beaker in excess of 25cm³ making sure to mark the beaker.
- Using a funnel measure out 50cm³ of KOH into the burette making sure the bottom of the meniscus on the line 0cm³.
- Measure 25cm³ of KOH into the polystyrene cup.
- Place thermometer into the cup and cover with lid.
- Start the timer and take readings of the temperature every 30 seconds.
- In another clearly marked beaker, pour over 25cm³ of H2SO4.
- Put pipette filler onto pipette being careful not to break the volumetric pipette.
- Place the pipette into the beaker with acid in it and fill the pipette until the bottom of the meniscus is on the line.
- The pipette is up to 25cm³ so that as long as the bottom of the meniscus is on the line it will be accurate.
- Wait until the timer has gone past 150 seconds and add the acid from the pipette.
- Carry on taking readings of the temperature every 30 seconds until the temperature becomes constant.
- Repeat the experiment with different concentrations of acid, making sure to use another burette for measuring the liquid.
Concentration Table
This table will help when trying to make different concentrations of acid.
Results Tables.
Analysis and Conclusion
The equation that I will use to find the ΔHr value is
ΔHr = m x 4.2 x ΔT x 20
For 1 mole solution
ΔHr = 50 x 4.2 x 9.5 x 20
= 39 900J
For 0.8 mole solution
ΔHr = 50 x 4.2 x 9.1 x 20
= 38 220J x 1.25
= 47 775J/mol
For 0.5 mole solution
ΔHr = 50 x 4.2 x 5 x 20
= 21 000J x 2
= 42 000J/mol
For 0.2 mole solution
ΔHr = 50 x 4.2 x 0.8 x 20
= 3360J x 5
= 16 800J/mol
For 0.1 mole solution
ΔHr = 50 x 4.2 x 0.1 x 20
= 420J x10
= 4200J/mol
When looking at the graphs they show a good pattern with an obvious relationship. As the concentration decreases so does the ΔT value, thus decreasing the value of ΔHr.
However, I know that my results must be in line with the data book value which is 58 000J/mol. My result for 1 mole is well off that result. It is 39 900J/mol. This result is 18 100J/mol below the expected result.
My results in general are rather random. My results for 0.5 mol and 0.8 mol are quite accurate. The 0.2 mol and 0.1 mol results are, however, completely wrong. When they are multiplied up to 1 mole they should be approximately 58kJ.
When the ΔT value for 1 mole is compared with the preliminary experiment one can see where the problem lies. The preliminary experiment shows a ΔT value of 12.5˚C, whereas the real experiment has one of 9.5˚C.
Evaluation
In my opinion the experiment that I did was not very reliable or consistent. I base this on the fact that my results vary in their answers.
I believe that many of my mistakes were my own fault. I don’t think that I was careful enough when pouring the liquids from one container to another. I also think that my measurement of concentrations may have been inaccurate. The amount of water I added may have been erroneous due to the fact that my burette was broken. Also, the temperature taking from the cup was difficult due to the awkwardness of the positioning of the thermometer. I don’t believe that my accuracy was very good. One of the main things that affected my experiment was the fact that I did different experiments on different days.
I believe that I could have made sure that my results were more accurate and reliable by making sure I
- Bent my head down to the same level as the thermometer reading to gain a reading.
- Re-did my results for the different concentrations of solution.
- Used a different burette when I realised that the first one was broken.
- Try and repeat results for averages and to make results more liable.
- Do all the experiments on the same day.
I did not have any anomalies in the singular results or
Graphs. However, when looking at my overall results and graphs compared to each other, one can see that there are obvious differences on how the results fit with each other. I believe that the reason for this is as I said above – there were many inconsistencies between the different results that I took.