Reaction of Citric Acid Solution with Baking Soda

Reaction of Citric Acid Solution with Baking Soda

Figure 1

Introduction

An endothermic process is a chemical reaction in which heat is absorbed. When we perform an endothermic reaction in a flask, it initially cools. Later, heat from the surroundings flows to the flask until temperature balance is established.

In this experiment we follow temperature and pH changes occurring during the reaction between citric acid solution and baking soda.

H3C6H5O7(aq)+3NaHCO3(s) → 3CO2(g)+3H2O(l)+NaC6H5O7(aq)

Prior to beginning this activity, state your problem and hypothesis:.

·  Open TextMaker (Start > Program > SoftMaker Office > TextMaker).

·  Give your lab report a title

·  Place your name/s on your document.

·  Type your problem and hypothesis.

·  Type the word “Results.”

·  Create a data table to include 5 rows and 3 columns. Type temperature and pH in the latter two columns; and type initial reading, final reading, difference, and qualitative observations in the latter 4 rows; include units for temperature.

·  Save your file as Citric acid and your last name (Citric Acid Smith, for example)

·  Open MultiLab (leave TextMaker open in the background), and conduct the following activity.

Equipment

·  Nova5000 data logger

·  Temperature sensor (-25 – 110°C)

·  pH sensor

·  pH electrode

·  Sensor cable (to connect pH sensor to Nova5000)

·  Container of tap water (to rinse pH electrode and to place pH electrode when not measuring pH)

·  25 mL of a 1.0 M citric acid H3C6H5O7 solution

·  100 mL graduated cylinder

·  10 grams baking soda NaHCO3 (approximately 5 level teaspoons)

·  Scale or balance to mass baking soda

·  Container or filter paper (on which to mass the baking soda)

·  Scoop or spoon (to use while massing the baking soda)

·  1 small polystyrene foam cup (9 oz)

·  1 large polystyrene foam cup (16 oz)

·  Safety goggles

Safety Precautions

·  Follow standard safety procedures for laboratory activities in a science classroom.

·  Safety goggles should be worn at all times.

·  Do NOT touch or bang the end of the pH electrode, as it will break

·  When not using the pH electrode, place the electrode in tap water. If the electrode dries out, it may damage.

·  Set the electrode storage solution container in an undisturbed area, so it does not spill.

Equipment Setup Procedure

1.  Connect the temperature sensor to the I/O 1 port.

2.  Connect the pH sensor to the pH electrode.

3.  Using a sensor cable, connect the pH sensor to the I/O 2 port.

4.  Click the Setup on the main toolbar and program the Nova5000 according to the setup specified below.

Data Logger Setup

·  Input 1: Temperature (-25 – 110°C)

·  Input 2: pH 0 --14

·  Rate: Every second

·  Samples: 200 samples (03:20 MM:SS)

Experimental Procedure

1.  Obtain and wear goggles.

2.  Pour 25 mL citric acid solution into the smaller coffee cup.

3.  Place the small polystyrene coffee cup into the larger polystyrene coffee cup.

4.  Open the pH electrode and rinse the bulb and lower end of the probe in running water.

5.  Place the temperature sensor and the pH electrode into the citric acid solution; this will allow the sensors to equilibrate prior to beginning the activity.

6.  Mass 10 g of baking soda and set it aside to use in a few moments.

7.  Click Run on the upper toolbar to begin recording data.

8.  Gently stir the citric acid in the smaller cup with the temperature sensor. Wait until readings from the sensors are stable (approximately 20 seconds). You will NOT stop the Nova until the end of the activity. The Nova program will end when the set time has expired.

9.  At 20 seconds or when the sensors have stabilized, add 10 grams of the baking soda to the cup. Do NOT stop the logger when the baking soda is added. The reaction will produce a gas! Stir gently with temperature probe until the Nova finishes collecting data. The logger will automatically end data collection after 3 minutes and 20 seconds.

10.  Save your file as citric acid and your last name (Citric acid Smith, for example)

11.  Toggle to TextMaker and add your qualitative observations to your data table.

12.  Clean up; the solution may be poured down the sink for disposal.

Data Analysis

·  While in MultiLab, place one cursor on the temperature curve.

·  Click Tools > Analysis > Statistics to find the maximum and minimum temperature readings.

·  Toggle back to TextMaker. In your data table, record the maximum and minimum temperature readings.

·  Use the calculator on the Nova (Start > Programs > Science and Math, CalcCE) to calculate the temperature difference.

·  Toggle back to TextMaker (leave the Calculator running in the background) and record the difference in temperature in your data table. Do not forget to use proper units.

·  Return to MultiLab and drag the cursor to the pH curve. Click on Tools > Analysis Statistics to find the maximum and minimum pH values.

·  Toggle to TextMaker. In your data table, record the maximum and minimum pH values.

·  Toggle to CalcCE and calculate the difference in pH.

·  Toggle back to TextMaker and record the pH difference in your data table.

·  Annotate both graphs. Return to MultiLab and place the cursor on the temperature graph at the highest temperature value, immediately before you added the baking soda. Use Add Annotation on the left side of the lower graphing tool bar to add this temperature value. Use the keyboard to type in the maximum temperature valve; use units. Use Move Annotation to position the annotation. Before adding an additional annotation, you must first remove the existing curosr, add the cursor again, and position the new cursor to the desired location. Now, annotate the final temperature value. Repeat the last steps to add the initial pH and the final pH values.

·  Click on annotation icon and add two more labels: label one graph temperature and the other pH. Remember to remove the cursor and add a different cursor prior to adding a new annotation.

·  Title your graph. Click on Tools Graph Title and type your title.

·  Click on Tools Copy Graph

·  Return to TextMaker. Place cursor beneath your data table; add 10 lines by clicking the “return key” ten times on the keyboard. Place the cursor one or two spaces below your data table and paste (Edit > Paste) your graph into your lab report.

·  Use CalcCE to calculate the total heat lost by the solution: Heat lost = m Cp ΔT (mass X specific heat capacity of the solution X change in temperature). Because the citric acid solution is a weak aqueous solution, use the specific heat capacity of water (4.18 J/g °C). Your mass will be 25 g (25 mL of citric acid solution placed into the cup). The unit for heat is Joules.

·  Toggle back to TextMaker and place the total heat lost below your data table on your lab report. Place the cursor two lines beneath the total heat lost value. Include your formula and substitution values.

·  Beneath your graph, type your conclusion. Your conclusion should be in paragraph form and should include the answers to the Questions below.

Questions

1.  What was your problem?

2.  Restate your hypothesis.

3.  Was your hypothesis correct or incorrect?

4.  What happened to the temperature during the reaction? Use numbers from your data table as quantitative evidence for what happened. Do not forget units.

5.  What was the total heat loss during the reaction? Indicate how you calculated this value. Use proper units.

6.  What happened to pH during the reaction? Use numbers from your data table as quantitative evidence for what happened.

7.  Based on pH, what kind of chemical reaction occurred?

8.  What qualitative evidence indicated that a chemical reaction was taking place?

9.  Based on temperature, was this an exothermic or an endothermic reaction? Why?

10.  What gas was produced in this experiment?

11.  How might this lab be extended?

Further Suggestions

1.  Change the relative amounts of citric acid. Follow changes in temperature and calculate the heat of reaction.

2.  Change the relative amounts of baking soda. Follow changes in temperature and calculate the heat of reaction.

Teacher Notes

To prepare a 1 M citric acid solution, dissolve 25 of citric acid in 100 mL of water.

An example of the temperature graph obtained in this experiment is shown below. If you want labels for both temperature and pH to appear on the Y-axis, copy and place two graphs on the lab report in TextMaker. While in MultiLab, use the dropdown arrow above the graph to show I/O-1 and I/O-2.

Example of equation calculation:

Heat of reaction = (25 g) (4.18 J/g 0C) (15.500 C) = 1620 Joules (students’ temperature changes vary)

Possible answers to questions

1. What was your problem?

Will vary but should indicate what will happen to the pH and temperature of a citric solution when baking soda is added.

2. Restate your hypothesis.

Will vary, but should answer the problem and should be stated in an “if, then” form.

3. Was your hypothesis correct or incorrect?

Will vary, but should be consistent with hypotheses and what actually occurred.

4. What happened to the temperature during the reaction? Use numbers from your data table as quantitative evidence for what happened. Do not forget units.

Will vary, but should be indicate the maximum and minimum temperature and pH values shown on students’ graphs and data tables.

5. What was the total heat loss during the reaction? Indicate how you calculated this value and unit proper units.

Will vary. Heat of reaction = (25 g) (4.18 J/g0 C) (15.50 C) = 1620 Joules, for example.

6. What happened to pH during the reaction? Use numbers from your data table as quantitative evidence for what happened.

Will vary, but pH increased. Students should use specific numbers that were recorded in their data tables for support this increase.

7. Based on pH, what kind of chemical reaction occurred?

Neutralization reaction

8. What qualitative evidence indicated that a chemical reaction was taking place?

Bubbles were observed. A fizzing sound was heard.

9. Based on temperature, was this an exothermic or an endothermic reaction? Why?

Endothermic; heat was absorbed during the reaction, causing a decrease in temperature.

10. What gas was produced in this experiment?

CO2

11. How might this lab be extended?

The amounts of citric acid or the amounts of baking soda might be varied to see how this would affect the reaction.