General Chemistry 1 Lab, Assignments of Chemistry

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Determination of the Specific Heat of an

Unknown Metal by Calorimetry

General Chemistry I

Objective:

• The purpose of this lab is to experimentally determine the specific heat capacity of an unknown metal. This value, along with the density, will be used to determine the identity of the metal. Experimental :
• First, start by weighing the metal sample (25 - 40 g) to 0.0001 g and record the weight. Heat the metal in a boiling water bath for 15 minutes, ensuring it fits inside a polystyrene cup submerged in water. While heating, weigh two nested foam cups (coffee cup calorimeter). Add 60 mL of water to the inner cup and record its mass. Measure and record the temperature of the boiling water bath. Using a room temperature thermometer, measure and record the temperature of the water in the calorimeter every 30 seconds, starting two minutes before adding the metal. Transfer the metal to the calorimeter, record the initial temperature, and stir gently. Continue recording the water temperature every 30 seconds for 8 minutes. Repeat the procedure with the metal sample in an ice water bath instead of boiling water. Dry the metal sample thoroughly before each trial. Graphs: Figure I: Association between time and temperature for 12 minutes for Part A.

➢ Calculations:

1. Procedure 1: ∆𝑇 ℃ 𝑚𝑒𝑡𝑎𝑙

For the water: water reaches thermal equilibrium at 22.6℃ ∆𝑇 ℃ 𝑤𝑎𝑡𝑒𝑟 = 22. 6 − 18. 7 = 3. 9 Procedure 2: ∆𝑇 𝑚𝑒𝑡𝑎𝑙 = 2. 9 − 3. 8 = 0. 9 ℃ For the water: water reaches thermal equilibrium at 4.9 ℃ ∆𝑇 𝑤𝑎𝑡𝑒𝑟 = 4. 9 = 3. 2 = 1. 7℃

• So, for Procedure 1, the temperature change for the metal is 1.8°C and for the water is

3.9°C.

• For Procedure 2, the temperature change for the metal is −0.9°C and for the water is

1.7°C.

𝑚𝑒𝑡𝑎𝑙

𝑚𝑒𝑡𝑎𝑙

𝑚𝑒𝑡𝑎𝑙

𝑤𝑎𝑡𝑒𝑟

𝑤𝑎𝑡𝑒𝑟

𝑤𝑎𝑡𝑒𝑟

41. 286 𝑥 𝐶 𝑚𝑒𝑡𝑎𝑙 𝑥 (4. 9℃) = 60. 0902 𝑥 4. 184 𝑥 (− 0. 8) − 202. 2965𝐶 =− 201. 1339174 𝐶 0.994253076 = 0.99 J/(g* ℃ ) 𝑚𝑒𝑡𝑎𝑙 =

➢ Post Lab Questions:

1. There are 2 significant figures in the specific heat because the lowest number in the calculations has 2 sig figs.
2. The closer metal match to our specific heat was magnesium with a specific heat of 1.020. Percent Error: = (experiment-actual) / actual) x 100 = (0.99 - 1.020) / 1.020) x 100 (-0.03 / 1.020) x 100 = 2.94 % error Possible errors: ● The unknown metal sample may cool in the air during transfer to the calorimeter. ● Heat can be lost through the heating chamber , also heat can be lost through the thermometer. ● The specific heat of the calorimeter (foam cup and water) may be slightly different than just the specific heat of water. ● Non-uniform heating of the water measuring the temperature in a 'hot' or 'cold' spot. If stirring the water to prevent non-uniform heating, the addition of energy to the water, from the stirring device. Conclusion: In summary, according to the website engineersedge, it was found that the closest metal with our experimental specific heat of 0.99 J/(g *℃) is Magnesium. On the website it states that Magnesium has a specific heat of 1.020 J/(g *℃). The percent error for this procedure and determining the meal was calculated to be 2.94%.