Heat of Combustion of Naphthalene

Q1. General procedure:

Procedure of bomb calorimetry experiment consists of several steps:

(a) Preparing water jacket: Empty water bucket is taken and 2 kg of water is added to it by weighing. Then this water bucket is placed in the insulated chamber.

(b) Making pellets of solid sample: A certain amount of solid sample is weighed and putted in the sample holder of the pellet press to make a pellet. After this, the weight of the pellet was also noted.

(c) Charging the bomb: The pellet of known mass is placed in combustion cap. A fusing wire is cut into a piece and its length is measured by scale. Then the wire is wrapped around the electrodes to provide electrical charge and placed such that the wire touches the pellet physically. Some little amount of water (need not to measure) is taken form that 2 kg water and taken in the stainless-steel bomb container. The container is fixed with the holding stand and lid and locked.

(d) Addition of oxygen from cylinder: Oxygen gas outlet tube from cylinder is attached with the gas inlet of the bomb container and it is allowed to flow oxygen. Initially, the bomb was pressurized with oxygen and discharged to remove any nitrogen content present inside the bomb. Now, finally the bomb is again pressurized with oxygen at 20 atm pressure.

(e) Putting bomb in calorimeter water jacket: Oxygen filled bomb is placed carefully inside the calorimeter using a tongue ensuring there is no leakage of oxygen from the bomb (can be checked by visualizing no steady stream of bubbles coming out of the bomb).

(f) Completing calorimeter assembly: Then electrodes are attached for firing and the lid is putted with stirrer. Stirring is started to ensure uniform distribution of temperature inside the bucket. Thermometer is fitted and the temperature is recorded. Wait for some more minutes until temperature is steady and now it is ready to fire.

(g) Firing the bomb: Fire button is to be pushed by keeping an eye on flash. The temperature change (increase or decrease) is monitored and recorded at regular time interval until a steady temperature is achieved. Then bomb container is to be taken out and the pressure was discharged. After equalizing the pressure, head of the bomb is removed. The container is checked if complete combustion occurs or not. After that, the remaining part of the fuse wire is taken out and measured the length of wire left over. This will give an estimate of how much wire burnt.

1. Differences between calculated and observed combination/overtone...