The length of time the water is heated for is important as a short period of time will not heat the water sufficiently enough to take accurate results. However, heating the water for too long will boil the water to 100i?? C and therefore the results will not show any trend, as this is the maximum temperature for water. I chose to heat the water for 150 seconds (2. 5min) as this was a suitable time. METHOD * Set-up apparatus as shown in diagram. Fill calorimeter with 100cmi?? of distilled water and record temperature in i?? C with thermometer for 30 seconds to allow an accurate reading.
Read thermometer at eye level in order to reduce parallax error due the reflection of light through the glass. Select burner and check the height of the flame is 4cm using a ruler. Change length of wick using tweezers to change the height of the flame. Weigh the burner filled with the desired alcohol with the lid on it using a top pan balance. Ensure the balance is on a flat stable surface and place burner on pan gently in order to keep reading accurate. I shall use the first four alcohols in the series: methanol, ethanol, propan-1-ol and butan-1-ol.
Record mass in grams to the nearest hundredth. Clamp the calorimeter 7cm above the top of the burner and place lid on calorimeter properly. Measure the height of calorimeter above burner using a ruler. Place burner on a heat-proof mat, under calorimeter; remove burner lid and light immediately with a match. Withdraw match immediately as the heat of the wood combusting could effect the temperature of the water in the calorimeter. Begin timer immediately when wick is lit. Do not remove lid before match is lit as some alcohol may evaporate and alter the burners weight before it is lit.
Plunge stirrer up and down once every 5 seconds to ensure uniform heating. During heating keep lid on calorimeter to prevent the water evaporating and heat loss. Record waters temperature every 30 seconds by using thermometer at eye-level. Do not remove thermometer from water to take reading, as this will change its temperature. After 150 seconds of heating extinguish flame by replacing burner’s lid. Record the water’s final temperature in i?? C. Re-weigh burner and record mass in grams to the nearest hundredth. Repeat 3 times and take an average of results. Repeat for all four alcohols.
Calculate energy released by each alcohol per gram using the formula below: Energy Released per gram= C x Mw x /\T (J/g) Mf Where, C= specific heat capacity of water (4. 17 J/gi?? C) Mw=mass of water (g) /\T=change in temperature (i?? C) Mf=Mass of fuel used (g) Calculate energy released per mol using average J/g and the following formula: Energy released per mol= Mr x J/g (J/mol) Where, Mr=molecular mass J/g=Energy released per gram (average) Safety Precautions Because this investigation involves the use of open flamed burners, I will need to be very careful in the laboratory.
I will remove all loose pieces of clothing that may fall into flame and set light. I will wear safety goggles to protect my eyes as I am heating a liquid, which could spit, into my eyes when hot. I will use a heat-proof mat to protect the workbench from the heat of the burner. I will abide by all standard laboratory rules such as: Do not run. Results PTO CONCLUSION The graph shows that as the length of the molecule chain in an alcohol increases so to does the amount of energy it gives of when completely combusted.
The curved ‘line of best fit’ shows that the relationship is not proportional. The energy released increases because as the length of molecule chain increases because the larger chains only need a small input of energy to break the original bonds yet gives out a larger amount of energy when the new bonds are formed. The energy of the products is lower compared to that of the reactants in longer chain molecules than smaller ones. The results support my prediction in the way that I predicted that as the length of the chain increased so to would the energy released.
However, I also predicted that the graph would show directly proportional results, which it does not. My prediction also stated that the results would be lower than the theoretical values due to heat loss which proved to be correct. EVALUATION I believe the method I used was as accurate as possible with the equipment provided, although the results do not show this. The energy released per mol values are a lot lower than the theoretical values due to heat loss. Because of the large amount of heat loss the results are quite varied and unreliable.
I only encountered one anomalous result, which is highlighted in red on the results table. I believe this is because of less heat being lost during this test than the was lost during the other tests for propan-1-ol. To overcome this problem barrier could be placed around the burner to shield it from drafts and guide the heat towards the calorimeter. I believe that the results show a curve because more heat was lost for the small-chained molecules due to the lower temperatures of flame being blown away more easily than those flames with higher temperatures.