Endothermic and Exothermic Reactions with lab notebook report PDF

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CH106 – Exothermic and Endothermic reactions

Endothermic and Exothermic Reactions PRE-LABORATORY INTRODUCTION: Many chemical reactions give off energy. The energy change in a chemical reaction usually manifests itself in the form of thermal energy, or heat. Chemical reactions that release energy are called exothermic reactions. Some chemical reactions absorb energy and are called endothermic reactions. You will study one exothermic and one endothermic reaction in this experiment. By observing a temperature change during a reaction, the direction of heat flow can be determined as heat flow and temperature are directly proportional. Experimentally, calorimetry experiments are used to determine the energy change during a chemical reaction and measurements are often made using a device called a calorimeter. Accurate values for heat flow can be obtained with a bomb calorimeter, but these are expensive and sometimes hard to use. We will use a simpler, cheaper, and faster calorimeter made from a Styrofoam coffee cup, as shown in Figure 1. The cup itself is a good insulator.

In Part I, you will study the reaction between citric acid and sodium bicarbonate (or more commonly, baking soda). An equation for this reaction is: H 3 C 6 H 5 O7 ( aq )+3 NaHCO 3 ( s ) → 3CO 2 ( g )+3 H 2 O ( l )+ Na3 C6 H 5 O 7 (aq) In Part II, you will study the reaction between magnesium metal and hydrochloric acid. This is the same reaction you would have seen in the Ideal Gas Law Lab (CH 105). An equation for this reaction is: Mg ( s ) +2 HCl(aq)→ H 2 ( g ) + MgCl2 (aq) This lab is adapted from Chemistry with Vernier. End of Pre-Laboratory

CH106 – Exothermic and Endothermic reactions

Endothermic and Exothermic Reactions OBJECTIVE: Study one exothermic and one endothermic reaction. SAFETY PRECAUTIONS: Hydrochloric acid is caustic. Avoid spilling it on your skin or clothing. Wear chemical splash goggles and lab coats at all times. Do not breathe the hydrogen gas vapors!

EXPERIMENTAL PROCEDURE: (Working in pairs) Setting up the Vernier tablet: Plug the Vernier tablet in and turn it on from the power button on the top. Once the startup is complete, plug the temperature probe into “CH 1” on the left side of the tablet. You should see the temperature displayed in ⁰C. If you do not see the temperature or if it is not in Celsius, please consult your TA or instructor before moving on. Part I - Citric Acid plus Sodium Bicarbonate: Place a Styrofoam cup into a 250 mL beaker as shown in Figure 1. Measure out 30 mL of citric acid solution and put it into the Styrofoam cup. Place the Temperature Probe into the citric acid solution. Weigh out 10.0 g of solid sodium bicarbonate on a piece of weighing paper. The temperature probe must be in the citric acid solution for at least 30 seconds. Record this temperature. Begin data collection by clicking the green “play” button on the bottom left corner of the screen. A graph should appear and the temperature will be recorded for a maximum of 180 seconds. After about 20 seconds have elapsed, add the sodium bicarbonate to the citric acid solution. Gently stir the solution with the Temperature Probe to ensure good mixing. Continue to collect data until the temperature has leveled off. Record this temperature in your notebook. When finished collecting data, the solution can go down the drain. To analyze your data, tap the “Analyze” button at the top of the screen. Choose “Statistics” then press “Temperature”. In the statistics box that appears on the graph, several statistical values are displayed for the run, including minimum and maximum. In your lab notebook, record both the maximum and minimum temperatures along with the times they occurred. To confirm the temperatures, click on the graph to see the points or click on the table button in the right top corner to see all the points listed in table format. Compare the minimum and maximum data points to those you recorded in real time. The points should be similar. The temperature with the longer time will be your final temperature, t 2 and the temperature with the shorter time will be your initial temperature, t1.

CH106 – Exothermic and Endothermic reactions Part II – Hydrochloric Acid plus Magnesium Reset the Vernier tablet for data collection by pressing “File” then “New”. You will be asked if you want to save the previous data, MAKE SURE YOU HAVE RECORDED THE TEMPERATURES FROM PART I, then press “Discard”. Measure out 25.0 mL of DI H2O and put it into the EMPTY Styrofoam cup then add 5.0 mL of 6.0 M HCl solution to the water. This will give you a total 30.0 mL HCl solution. Place the Temperature Probe into the HCl solution and stir. Note: The temperature probe must be in the HCl solution for at least 45 seconds before moving on. Obtain a piece of magnesium metal. Begin data collection the same way as Part I by clicking the green “play” button on the bottom left corner of the screen. A graph should appear and the temperature will be recorded for a maximum of 180 seconds. After about 20 seconds have elapsed, record the temperature then add the Mg to the HCl solution. Gently stir with the temperature probe to ensure good mixing. CAUTION: Do not breathe the vapors! Continue to collect data until the temperature has leveled off. Record this temperature in your notebook. When finished collecting data, the solution can go down the drain. Analyze your data the same as in Part I, tap the “Analyze” button at the top of the screen. Choose “Statistics” then press “Temperature”. In the statistics box that appears on the graph, several statistical values are displayed for the run, including minimum and maximum. In your lab notebook, record both the maximum and minimum temperatures along with the times they occurred. To confirm the temperatures, click on the graph to see the points or click on the table button in the right top corner to see all the points listed in table format. Compare the minimum and maximum data points to those you recorded in real time. The points should be similar. The temperature with the longer time will be your Final temperature, t 2 and the temperature with the shorter time will be your Initial temperature, t1.

CH106 – Exothermic and Endothermic reactions

LAB REPORT: Endothermic and Exothermic Reactions Complete this lab report as if it were your lab notebook. The purpose and experiment summary should be completed before lab. The procedure, observations and data should be completed during lab. The calculations, conclusion and post lab questions can be completed after lab.

Name:

__Julia Bell____________________________

Date Experiment was performed:

_4/13/21____________________________

Purpose: - Study exothermic and endothermic reactions - Monitor the temperature change of two different reactions to identify whether they release or absorb heat energy

Experiment Summary: In this lab, we looked at one exothermic and one endothermic reaction, and the overall concept of energy transfer between a system and its surroundings, using a styrofoam coffee-cup calorimeter and a vernier tablet. To do this, we looked at a reaction that occurs between citric acid and sodium bicarbonate, as well as a reaction between hydrochloric acid and magnesium.

CH106 – Exothermic and Endothermic reactions Notes from Pre-Lab Lecture: 1. All chemical reactions involve the transfer of energy - Endothermic: Requires energy input of energy (positive change in enthalpy) - Exothermic: Releases energy upon completion (negative change in enthalpy 2. How to use a repipet: Lift to draw up the liquid and press down to dispense 3. Hazards: 6M hydrochloric acid is caustic, wear splash goggles, lab coats, and gloves - Do NOT breathe in hydrogen gas vapors

Procedure

Setting up Vernier tablet: - Plug the Vernier tablet in and turn it on from the power button on the top - Plug the temperature probe into “CH 1” on the left side of the tablet Citric acid plus sodium bicarbonate: - Place a Styrofoam cup into a 250 mL beaker - Measure out 30 mL of citric acid solution and put it into the Styrofoam cup - Weigh out 10.0 g of solid sodium bicarbonate on a piece of weighing paper - Place the temperature probe in the Styrofoam cup and record the temperature Citric acid plus sodium bicarbonate (cont.): - Tap the “Analyze” button at the top of the screen to analyze the data - Choose “Statistics” then press “Temperature”. In the statistics box that appears on the graph, several statistical values are displayed for the run, including minimum and maximum. - Record both the maximum and minimum temperatures along with the times they occurred. - To confirm the temperatures, click on the graph to see the points or click on the table button in the right

Observations and Data

35 seconds in citric acid: 20.6C 180 seconds with sodium bicarbonate added: 10.1C Gradually decreased over time

CH106 – Exothermic and Endothermic reactions top corner to see all the points listed in table format. Compare the minimum and maximum data points to those recorded in real time. Hydrochloric acid plus magnesium: - Reset the Vernier tablet for data collection by pressing “File” then “New.” Discard previous data after recording - Measure out 25.0 mL of DI H2O and put it into the EMPTY Styrofoam cup then add 5.0 mL of 6.0 M HCl solution to the water - Add 5.0 mL of 6.0 M HCl solution to the water. - Place the Temperature Probe into the HCl solution for 45 seconds and stir. Hydrochloric acid plus magnesium (cont.): - Obtain a piece of magnesium metal. Begin data collection the same way as Part I. - After about 20 seconds have elapsed, record the temperature then add the Mg to the HCl solution. Gently stir with the temperature probe to ensure good mixing. - Record data until it levels off - When finished collecting data, the solution can go down the drain.

20 seconds with HCl: 21.7C 114 seconds with Mg added: 35.2 Gradually increased over time

Note: You may not need every block but if you need more just continue on another sheet of paper.

Procedure

CH106 – Exothermic and Endothermic reactions Observations and Data

Balanced Chemical Reactions: Note any important chemical reactions from this lab. H 3 C 6 H 5 O7 ( aq )+3 NaHCO 3 ( s ) → 3CO 2 ( g ) +3 H 2 O (l ) + Na3 C6 H 5 O 7 (aq) 1. - Citric acid and sodium bicarbonate 2. Mg ( s) +2 HCl(aq)→ H 2 ( g) + MgCl2 (aq) Magnesiummetal∧hydrochloric acid -

Data Summary: Part I Final temperature, t2

10.1C

Part II 35.3C

Initial temperature, t1

20.6C

21.7C

Temperature change, ∆t (∆t = t2 – t1)

-10.5

13.6

CH106 – Exothermic and Endothermic reactions Calculations: Show all work!

Conclusions: By watching the change in temperature through the reaction between citric acid and sodium bicarbonate and hydrochloric acid and magnesium and analyzing this temperature change using a vernier tablet, we noted the differences between exothermic and endothermic reactions. With a negative ∆t value of -10.5C and a steady decrease in temperature over time from 20.6C to 10.1C, the reaction between citric acid and sodium bicarbonate was exothermic. On the other hand, with a positive ∆t value of 13.6 and a gradual increase in temperature over time from 21.7C to 35.3C, the reaction between hydrochloric acid and magnesium was endothermic.

Post Lab Discussion Questions: 1. Tell which reaction is exothermic. Explain. The reaction between citric acid and sodium bicarbonate (baking soda) is exothermic because the ∆t value for this reaction is negative at -10.5C, indicating a release of heat. Likewise, we can see the initial temperature of 20.6C decreases to a final temperature 10.1C.

2. Which reaction had a negative ∆t value? Is the reaction endothermic or exothermic? Explain. The reaction between citric acid and sodium bicarbonate had a negative ∆t value of -10.5C, which means the reaction is exothermic and releasing heat to the surroundings.

3. For each reaction, describe three ways you could tell a chemical reaction was taking place. In both reactions 1 and 2, the solution fizzed and bubbled as the sodium bicarbonate (reaction 1) and magnesium (reaction 2) were added. Also, the temperatures changed over the duration of the reactions, indicating that a reaction was occurring; in reaction 1 the temperature decreased and in reaction 2 the temperature increased. Lastly, for the second reaction, you could tell the reaction was occurring because of the formation of hydrogen vapors.

CH106 – Exothermic and Endothermic reactions 4. What is the molarity of the 30.0 mL HCl solution that you placed the Magnesium in? The molarity of 30.0mL HCl solution that I placed the Magnesium in is 1.0M.

CH106 – Exothermic and Endothermic reactions

CH106 – Exothermic and Endothermic reactions 5. Can you think of possible sources of error in your measurements? Some possible sources of error in your measurements may include not measuring the correct amount of sodium bicarbonate, not allowing the vernier tablet to sit in the cup for enough time before recording the data and proceeding with the reactions, and entering data incorrectly into the calculator when finding ∆t....