SAFETY
There are a number of Safety Precautions that I will have to consider during this experiment:
I will have to wear eye protection (goggles) because I will be handling corrosive materials. I will be cautious on keeping then equipment I am using, away from the edges to avoid any breakages or spills.
PREDICTIONS
From my knowledge of Chemistry and Enthalpy Change of Combustion, I know that for example Methanol will need a
Total of 2039 KJ mol-1 to break the bonds and form new ones. I predict that 2-Methyl-Propan-1-ol will have the largest Enthalpy change because it has more bonds, which needs more energy to break and form new bonds. It will need around 5558 KJ mol –1
METHOD
I will start this experiment by collecting the apparatus that I will be using. Using the measuring cylinder, pour 100ml of water into steel cubicle and record the temperature of the water. Join the cubicle to the clamp stand at a distance of 17cm from the base. The distance will need to be kept the same in all the experiments or it will not a fair test. Secondly, using the second 100ml-measuring cylinder, measure 100ml of the specific Alcohol being used and pour it into a sprit burner. For safety, make sure this procedure is operated within a fume cupboard to prevent fumes from escaping out into the classroom. Alcohols are known to be dangerous chemicals, so it is important that they are not it contact with the user. Thirdly, place the sprit burner beneath the cubicle and light the wick using a light from the Bunsen. While the wick is still burning, Start the stopwatch and using both cardboard shields, grasp them around the sprit burner tightly similarly to a cubical shape to prevent heat loss. This is because the experiment will be affected if most of the heat energy escapes and suffienct amounts of heat energy can only be used to heat the water. Keep the shields held tightly together until 3 minutes are over. I decided to time the experiment for a specific time length because then it helps in comparing the Alcohols. Repeat the experiment for all the alcohols until left with 2 sets of results for each Alcohol. This helps in identifying any mistakes.
ANNALYSING
RESULTS 1
RESULTS 2
AVERAGES RESULTS 1+ RESULTS 2/2
The results show that Butan-1-ol and 2-Methyl-Propan-2-ol weighed the highest whereas Methanol weighed the lowest. This point connects to the chemistry of the Alcohols which also state that Butan-1-ol weights 74.1 g mol –1 and 2 Methyl Propan-2-ol also weights around 74.1 mol –1. The temperature of the water in the experiments using Alcohols, Butan-1-ol and Butan-2-ol had the largest increase.
The results also show that most of the Butan-1-ol Alcohol fuel was burned compared to the other alcohols. An anomalous result appeared in the weight of fuel burned for Propan-1-ol because at the end, the sprit burner had gained weight, which somehow affects my results.
Expt 3(Evaluation)- Determining the Enthalpy change of a reaction
Finding the Enthalpy change of a reaction when Sodium Carbonate decomposes after being heated to form Calcium oxide and Carbon Dioxide is difficult to measure directly. The enthalpy change could be measured through a simple approach through Hess’s Law. In this experiment, Calcium Carbonate and Calcium oxide were reacted separately with hydrochloric acid. An enthalpy cycle could then be used to determine the enthalpy change of the reaction.
∆H1=∆H2+∆H3
To find the mass, the density needs to be multiplied by the volume to find ∆H2 and ∆H3.
Enthalpy change for ∆H2:
Heat = M x C x ∆T
HEAT = 50 x 4.2 x 4 = 840 kJ
50 * 2 /1000 = 0.1 Mol
∆H2 = 840 KJ/ 0.1 Mol = 8400KJ –1
Enthalpy chnge for ∆H3:
HEAT = 50 x 4.2 x 9 = 1890 kJ
50 x 2 /1000 = 0.1 Mol
∆H3 = 1890 KJ/ 0.1 Mol = -18900KJ –1
∆H1 = 8400 KJ Mol-1 (∆H2) – -18900 KJ Mol –1 (∆H3)
= -10500 KJ Mol –1
The experiment proceeded successfully but there were some key factors that may have affected the results.
Suitability of experimental procedures
There are some factors in the experiment that can be improved if the experiment was repeated. Firstly, the weigh in machine was not suitable for this experiment because it weighed substances to one decimal point (e.g. 2.5) and can be made more accurately by using a weigh that weighs up to four decimal places. Secondly, the experiment was performed in a container with poor insulation and therefore some of the heat may have escaped. If I had the chance to repeat the experiment, I would perform the experiment in a closed insulated container such as a Bomb Calorimeter. This could then minimise the chance of any errors occurring within the experiment.
Anomalous Results
According to the results that I received, there were no anomalous results but I would repeat the experiment just to be sure that there were no anomalous results.
Sources of error
There may have been a number of errors within this experiment that could have been avoided. Firstly, the mass of Calcium Oxide and Calcium Carbonate should have been kept the same to allow the experiment to be a fair test. Also, a more accurate thermometer could have been used to determine the temperature change
