Calorimetry Experiment to Identify Unknown Metal

Calorimetry Lab Report

Introduction

The process of measuring the amount of heat released or absorbed during a chemical reaction is known as calorimetry. Because calorimetry is used to measure the heat of a reaction, it is a crucial part of thermodynamics. By knowing the change in heat, it can be determined whether or not a reaction is exothermic or endothermic. Which can be used to determine the specific heat of a substance. The purpose of the lab calculates the specific heat value of a known and the unknown metal through the observations and results gathered about the release and absorption of the heat throughout the experiment. Then use the specific heat of the unknown metal to identify the metal.

Materials

●       Hot plate

●       250 mL Beaker

●       100 mL Graduated cylinder

●       Thermometer

●       String

●       Copper and unknown metal

●       Balance (scale)

●       Timer

●       2 styrofoam cups with lids

Experimental

The personal protective equipment required in the experiment were gloves, goggles and an apron. In the experiment, a hot plate, beaker, graduated cylinder, thermometer, string, copper, unknown metal, balance, timer, 2 styrofoam cups with lids are used. First the mass of the copper was found then recorded in the data table. 100 mL of water was poured into a 250 mL beaker then placed onto the hot plate. Then the hot plate heat dial was turned on to the highest setting. The string was tied to the piece of copper then when the water was boiling the copper was carefully placed into the beaker of boiling water and the string was hung over the side of the beaker. After the copper had boiled for two minutes. While it was boiling the 100mL graduated cylinder was used to measure 100 mL of water. The mass of the styrofoam cup without the lid was found then recorded in the data table. Then the 100 mL of tap water was poured into the styrofoam cup. After that the temperature of the tap water was found and recorded. That is the initial temperature of the water. After that the mass of the styrofoam cup and the water was found and recorded on the data table then the lid was placed on the cup and that cup was placed inside the second cup. Then the mass of the water was calculated and recorded. After that the temperature of the boiling water was found when it was made sure that the thermometer was not touching the glass beaker or piece of metal. That is the initial temperature of the metal. Then the string was used to move the copper into the cold water and the lid was quickly placed on it. Then the thermometer was placed through the straw hole in the lid and the cup was gently swirled until the temperature stopped changing. When the temperature of the water with the metal stopped changing the temperature was recorded on the data table. After that all the steps were repeated with the unknown metal at the station once the styrofoam cup was dried off. After all the steps are completed the station is cleaned up. The metal is removed from the cup and the metal the string and the thermometer are all placed on a piece of paper towel to dry. The water was poured into the sink and a piece of paper towel was used to dry the cups. Then the hot plate was turned off and unplugged. Then if the beaker was cool enough to touch it was placed upside down on a paper towel.

Results and Discussion

Based on the results of this experiment, it can be determined that the unknown substance can be identified as titanium. This is based off of the calculations made based of the specific heat and energy of the copper as well as the sample of the previously unknown metal. Table 1 identifies the masses and temperature of the copper and the water throughout the first section of the experiment.

Table 1. Observations and Measurements Using Copper

This substance is copper but there is a big margin of error in the results. The accepted specific heat value of copper is .385 J/g℃, but when the results are calculated in equation (1), the specific heat is .503 J/g℃.

1009.47 J = ___ J/g℃*76℃*26.4g (1)

In this equation, the amount of energy used is 1009.47 J determined by how much energy the water used in its processes, as displayed in equation (2).

_______ J = 96.6g*4.18 J/g℃*2.5℃ (2)

In this equation, the specific heat, temperature change, and mass of the liquid water are multiplied to find the amount of energy the process needs. The observations and measurements recorded from this part of the lab using copper allows the specific heat and energy amounts present throughout the experiment to be calculated.

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 The second section of the experiment is where the identity of the unknown substance, titanium, is determined. Based on the temperatures and masses recorded in Table 2, the specific heat and energy amounts of the water and metal can be calculated.

Table 2. Observations and Measurements Using the Unknown Substance

Using the mass and temperature of the water displayed in Table 2, the energy used in the specific heat equation of the liquid water can be calculated, as shown in equation (3).

_______ J = 2℃*97.6g*4.18J/g℃ (3)

In this equation, the temperature change, mass, and specific heat of the liquid water are being multiplied by one another to produce the energy needed to complete the process. Because the water and the unknown substance cooled together, the energy they will need is the same. That means 815.936 J are used in the specific heat equation for the unknown substance, as shown in equation (4).

815.936J = ____J/g℃*71℃*22.6g (4)

In equation (4), the energy needed, on the left side, is equal to the product of the specific heat, mass, and temperature change of the unknown substance, all of which were observed in the experiment and recorded in Table 2. This is not the accepted value heat of titanium, but it’s closest t titanium so the unknown substance’s identity is the metal titanium.

Conclusion

Using the relationship (q_water = -q_metal), the specific heat of copper can be calculated to be -.503. This is calculated using the equation of -76℃*26.4g*____ J/g℃ = 96.6g*4.18 J/g℃*2.5℃. The accepted specific heat value is .385 J/g℃, which different than the experiment’s results. Using the percent error formula and substituting in the results for coppers specific heat, it’s calculated that there is a 30.65% error with the results. The specific heat of the unknown metal can be determined to be .508 J/g℃. This is closest to the specific heat of titanium .523 J/g℃. The metal’s actual identity is aluminum, which is not the result that was determined from the experiment. Aluminum has a specific heat of .897 J/g℃, when in the experiment the result was a specific heat of .508 J/g℃. When using the percent error formula, it can be determined that the results had a percent error of 43.367%. Some places that could cause error in the experiment could be when taking the temperature if the thermometer touched a different substance or an error in measurement of the mass of and of the substances or if the wrong numbers were recorded unto the data table. Some error that were made were that it is possible that when taking the temperature, it had not cooled enough, or it touched a different substance or a wrong number was recorded on the data table. Some improvements that could be made are to be more exact and have more time allotted to the experiment and possibly make it so there is as little as possible percent error. Tap water has more minerals than pure water so its specific heat would be different resulting in completely different equation. The Law of Conservation of Energy can be observed through the transfer of heat and energy from the metal to the water. The negative sign is present in the heat relationship because the substances are cooling down. The unknown metal could have been determined in many different ways not using heat for example you could determine it by the density of the metal. This experiment explained calorimetry very well. It helped me understand that calorimetry is when heat is transferred between substances when they come touch each other while also showing how simple observations can be used to solve for amounts of energy or specific heat values.

References (American Chemical Society)

1. Chemistry for Majors. https://courses.lumenlearning.com/chemistryformajors/chapter/calorimetry/ (accessed Jan 6, 2019).
2. Chemteam
3. https://www.chemteam.info/Thermochem/Determine-Specific-Heat.html (accessed Jan 6, 2019).
4. 3.Libretexts. Calorimetry. https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Thermodynamics/Calorimetry (accessed Jan 6, 2019).
5. Roberts, A. Calorimetry Lab Procedures. Presented at Apex Friendship High School, Fall 2018.