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prac-calorimetry#2

# prac-calorimetry#2 - ∆ T = temperature change substitute...

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Determination of the heat of solution of a salt. Aim . To use the calorimeter to determine the enthalpy of solution of a salt such as potassium nitrate, KNO 3 . ie. to determine the value of H for the reaction KNO 3(s) K + (aq) + NO 3 - (aq) Procedure: 1. Accurately weigh approx. 3.0 g of finely powdered KNO 3 . Use a mortar and pestle to grind the salt into a fine powder. 2. Place 80 mL of tap water in the calibrated calorimeter; use a measuring cylinder to measure the volume of water as accurately as possible. Measure the temperature of the system and ensure that it reaches a constant value. Record this temperature. 3. Add the weighed sample of KNO 3 to the water, and stir to ensure that rapid and complete solution of the salt takes place. 4. Continue reading the temperature of the system, and record the temperature every 30 sec. for 3 minutes. Note the minimum temperature reached. 5. Using
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Unformatted text preview: ∆ T = temperature change, substitute into the formula q = (calibration factor) * ∆ T to determine the heat energy (q) accompanying this solution process. Since "q" is also given by the formula q = (no. of mol KNO 3 ) * ∆ H it then becomes possible to calculate an experimental value for ∆ H for the above reaction. 6. Complete a report on this experiment, and show all calculations. In addition, answer the following questions: (a) Why do we use 80 mL of water in this part of the experiment, and not (say) 100 mL ? (b) The specific heat of water is 4.18 J o C-1 g-1 . Explain what this means. ie. translate the information from scientific language into common language. (c) The Calibration Factor of the calorimeter and its contents should be > 334 J o C-1 . Why ? (d) What are the major sources of uncertainty in this experiment? List them....
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