Use the method of mixtures to find out the specific heat capacity of a mass of brass.
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Paanii Ansah-Kofi 11A August 2003 Measuring the Specific Heat Capacity by Method of Mixtures Aim: To use the method of mixtures to find out the specific heat capacity of a mass of brass. Hypothesis: Using this method of mixtures it should be possible to find out this value as the energy lost by the hot substance cooling down (brass), is equal to the energy gained by the cold substance heating up (water). Knowing that the S.HC. of water is about 4 200 J kg-1 K-1, we may find what this value is for brass. Apparatus: Method: * Firstly, the masses of both substances, brass and water, were measured on a weighing scale. * The brass was then heated over a Bunsen burner in a water bath for a certain time period.
The value tells us that brass needs only about a third the amount of energy that water needs, to heat a kilogram of it by one Kelvin. Another thing to conclude is that the formula cb = mwcw (Tmax-Tw) was suitable for this method, which follows the mb(Tb-Tmax) principle that the energy lost by the hot substance is equal to the energy gained by the cool substance heating up after the mixture. The formula is obtained by rearranging the formula that shapes the principle itself: mb cb(Tb-Tmax) = mw cw(Tmax-Tw). Evaluation: The main source of experimental error, like in most experiments involving the transfer of heat, was the loss of thermal energy into the surroundings. This was due mostly to apparatus; errors related to the procedure were in the most part less observable.
This energy would eventually go down but depending on where the thermometer was positioned the reading could have given at inaccurate indication towards the mixture's maximum temperature. The changes of temperature of the container were also not taken into account, which adds to experimental error. Where there is a high level of uncertainty, the results may be imprecise but not wrong. Especially the fact that the amount of error can hardly be accounted for also makes it difficult to judge the uncertainty here. A source (Encarta Encyclopaedia 2003) has quoted that the S.H.C. of wood is 1 760 Jkg-1K-1 and one would obviously expect that of brass to lay quite a bit below that with the other metals which range between 100 and 1 000 Jkg-1K-1. The value here suggests therefore a high uncertainty in our results.
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