The calorimeter got colder once the solute had dissolved in the water

The calorimeter got colder once the solute had

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- The calorimeter got colder once the solute had dissolved in the water. Quantitative Observations: Trial # Mass (g) T i (initial) ( ) T f (final) ( ) ΔT ( ) 1 13.3 23.5 19.0 -4.5 2 25.0 22.6 15.4 -7.2 3 17.0 22.5 16.3 -6.2
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Calculations: (Steven) Q water = mcΔT = (200 g)(4.184 J/g )(-5 ) · = -4184 J = -4.184 kJ Q metal = mcΔT = (8.34 g)(0.9 J/g )(-5 ) · = -37.53 J = -0.03753 kJ ΔH solution = Q water + Q metal = -4.184 kJ + (-0.03753 kJ) = -4.22 kJ nNH 4 Cl = 4.22 kJ 17 kJ / mol = 0.248 mol NH 4 Cl mNH 4 Cl = n mm × = (0.248 mol)(53.49 g/mol) = 13.27 g = 13.3 g (rounded to 3 sig figs) % Error (ΔT) = 00 5 5 −4.5 × 1 = 10%
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Graph: (Tomas) Explanation: (Tomas) The graph demonstrates a strong, negative relationship between mass and net temperatures. As the independent variable (mass of ammonium chloride) increases, the dependent variable (net temperature) decreases. A correlation of -0.94 solidifies that the relationship is indeed a strong, negative one and in turn, this graph verifies our initial judgement of the relation. Calculations regarding graph: (Steven) Equation of the line of best fit according to graph: y = -0.2138x - 2.025 To calculate required mass of NH 4 Cl to achieve a ΔT value of -5 based on equation of line where the units for y are in and the units for x are in grams: y = (-0.2138)x - 2.025 -5 = (-0.2138)x - 2.025 -2.975 = (-0.2138)x -2.975/-0.2138= x
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x = 13.915 g %Error based on graph = 13.915 g 13.915 g − 13.3 g 00% × 1 = 4.42% (rounded to 3 sig figs) Discussion: (Raybin) Our goal for the experiment was to cool a can of water by a difference of 5 in 5 minutes. Using calorimetry and an understanding of Hess’s law, we found out that we need 13.3g of Ammonium Chloride in order to achieve that. In our experiment, we found that 13.3g made a temperature difference of 4.5 , that is a 10% error from what we originally needed (5 -4.5 )/5 *100=%error). The calculated mass of NH 4 Cl at ΔT = -5 is 13.915 g which means the percentage error based on the graph is 4.42% (refer to calculations).
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  • Fall '14
  • Pell, Wendy

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