Acid Base Chemistry

Acid Base Chemistry

Big Chemistry Project

SME 401

Dominic Held

This packet includes five days of activities to be used in a high school chemistry class. These activities should accompany a 2-3 week long unit on acid base chemistry.

Activities:

· Rainbow Connection Demonstration- Introduces acids and bases in a visual way. Students will observe indicators and their response to changes in pH. They will also observe how pH change can be a reversible process. This could be the first day beginning a unit a acid base chemistry.

· Measuring pH of Household Chemicals- This two day activity should follow several days of instruction on acids and bases. The pH scale should also be introduced in terms of concentration of H+ and OH- ions. The second part of this experiment is dependent on the availability of computer interfaced probes. The procedure of this part should be expanded or supplemented accordingly. If probes are unavailable the second day may be omitted.

· How Does a Buffer Affect pH?- This experiment should follow a discussion of buffer solutions in terms of H+ cations, OH- anions, and disassociation of weak and strong bases. Students should also be able to recognize the acid and base components of conjugate acid/base pairs.

· Microscale Titration-This activity uses phenolphthalein to indicate when an acidic acid has been titrated with a NaOH solution. By knowing the normality of the NaOH solution and the amount of drops used to titrate the acidic acid solution, the normality of an acidic acid solution can be calculated. This experiment should follow several lectures on the normality of solutions. Students should also be familiar with different measures of concentrations including molarity and molality.

Teacher Support Materials:

Rainbow Connection Demonstration

Overview:

This demonstration will be an introduction to a weeks worth of activities exploring acid/base chemistry. Several different ph indicators will be used to produce a wide array of colors. These indicators will be colorless under acidic conditions, but when a base is added, they will produce the three primary colors. By carefully mixing the indicators, all the colors of the rainbow will be produced. Six beakers are filled with the same “mystery” liquids. Each glass beaker takes on a different color of the rainbow, despite the fact that the same liquids were added to each. These solutions can be used several times and have a good shelf life.

Teacher and Student Objectives:

· Shows the dramatic color change of solutions containing indicators at different pH levels.

· Demonstrates the reversibility of indicator color changes.

· Get students thinking about how H+ and OH- ions interact.

Who’s Being Taught?

This demonstration could be used in both junior and high school when covering acids bases and indicators. Class size can vary considerably. It could even be given to a large audience given the proportions are increase to increase visibility.

Strengths of Exercise:

· This is a vivid exercise that should hold the student’s interest.

· The idea that you are performing magic using ‘mystery’ solutions can be used to increase their interest.

· This demonstration makes a great introduction to acid/base chemistry.

· Easy disposal of chemicals.

How to Assess:

Assign the students the readings in their textbooks that begin with acid base chemistry. Be sure to include readings on pH indicators. Students then should have some understanding about how this lab was executed.

What to Look Out For:

· Precautions should be taken when making solutions. (Safety Glasses)

· Students will not be handling solutions so it should be safe if they don’t wear safety glasses. This would also depend on school policy.

· Beakers should be visible to the entire audience.

· Demonstration should be tested before presenting.

Technical Information:

The solutions in this demonstration should be prepared at least a day before the presentation.

Some thought should be given on how this demonstration should be given.

Materials:

· 6 250 mL Beakers

· 6 Indicator Solutions and 6 droppers

· 500 mL Acid-Alcohol Solution

· 1200 mL 0.012 M NaOH Solution

· 100 mL 0.2 M NaOH Solution and 1 dropper bottle

· 30 mL Glycerine Solution and 1 dropper bottle

· 1 Small Beaker (35 mL)

· 2 Large Pitchers

Procedure:

Indicators:

The following recipes are for the six different indicator solutions. Each recipe will produce 15 mL of solution. These solutions should be made at least one day in advance to allow the solutes to fully dissolve into solution. Use 15 mL of 95% ethanol as the solvent for all six solutions.

· Red- 0.4 g phenolphthalein plus 1.0 g m nitrophenol

· Orange- 0.15 g phenolphthalein plus 2.0 g m nitrophenol

· Yellow- 2.0 g m nitrophenol

· Green- 0.2 g thymolphthalein plus 2.0 g m nitrophenol

· Blue- 0.5 g thymolphthalein

· Violet- 0.3 g phenolphthalein plus 0.13 g thymolphthalein

Acid-Alcohol Solution:

Mix 250 mL 0.05 M aqueous sulfuric acid with 250 mL 95% ethanol. Transfer into a large pitcher.

NaOH Solutions:

Prepare 1200 mL of 0.012 M NaOH solution transfer into a large pitcher. Make sure you know which pitcher is the acid and which is the base.

Prepare 100 mL of 0.2 M NaOH solution and transfer into a dropper bottle.

Glycerine Solution:

Dissolve 10 mL of 18 M H2SO4 in 20 mL of glycerol. Transfer into a dropper bottle.

Before Class:

Arrange the six 250 mL beakers in a row so that they can be seen by the entire class. Carefully place 2 drops of indicator solution in the middle of the beaker in the order shown:

Let the indicator solution dry on the bottom of the glass. This should take about 30 minutes.

During Class:

Add 35 mL of the acid, making sure to carefully pour down the side of the beaker. Try not to disturb the dried indicator. This solution should remain clear.

Slowly fill each beaker half full with the 0.012 NaOH solution. Once again be careful not to disturb the indicator by pouring along the side of the beaker. The amount of this solution should not be enough to make the solution in the beaker basic, so the solution should remain colorless

Rapidly pour the 0.012 NaOH solution into the beakers nearly to the top. The color of the solutions should now be visible. You may have to stir the solutions in order to fully dissolve the indicator.

Add anywhere from 3-15 drops of the glycerine solution stirring vigorously. Prior testing should give you an idea how much is needed to raise the acidity of the solutions until they are clear.

Titrate each beaker back to its original color by adding the 0.2 M NaOH solution drop wise and stirring vigorously.

Sneak 2 droppers full of the glycerine solution into the large pitcher containing the 0.012 NaOH solution.

Pour the contents of each of the beakers into the now acidic NaOH-glycerine pitcher. Because of the acidity of this solution, the combined solution should be colorless.

The solution mixture in the pitcher can be poured down the drain.

Follow up:

Measuring pH of Household Chemicals

Overview:

Many common household chemicals have acidic or basic properties. Scientists use the pH scale to rate acidity in solutions. The pH of a solution is a measure of the concentration of hydrogen ions in that solution. There are several different ways to measure pH. A pH indicator can be used to qualitatively determine the acidity or basesity of a solution. pH indicators are usually weak acids or bases themselves. When introduced into a solution, they may bind to H+ (Hydrogen ion) in an acid or the OH- (hydroxide) ions in a base. The change in electron configurations of the indicator causes the indicator's color to change. In this activity we will use cabbage juice and pH paper to determine an estimate of several household chemical’s pH. For the second part of the lab we will use a computer interfaced probe to find a more accurate measure of these chemicals pH.

Objectives:

· Use red cabbage juice as a pH indicator by recording its color change in various chemicals.

· Use pH paper to obtain a more accurate measure of pH, including a numerical value.

· Set up and calibrate a computer interfaced pH probe.

· Use pH probe to take an even more accurate pH measure.

· Compare results and correlate a pH scale for the red cabbage juice indicator.

Materials:

Day 1:

· Red Cabbage Juice

· 6-Well Reaction Plates

· Transfer Pipettes

· Various Household Chemicals (Baking soda solution, solution of detergent, Soda, milk of magnesia, vinegar, glass cleaner, etc)

· pH Paper

Day 2:

· Computer Interfaced pH Meter (with instructions)

· Buffer Solutions for Calibration of Probe

· Six Small Beakers

Procedure:

Day 1: Correlating cabbage juice color and pH in various solutions using pH paper

1. Obtain a 6-well reaction plate. Label the wells 1-6

2. Obtain six different household chemicals and place them in individual wells. Use the chart below to record which chemical is in which well.

3. Use pH paper to determine the pH of each substance. Compare the color change of the paper to the key given with the pH paper. Again use the chart below to record your results.

4. Using a transfer pipette, add 5 drops of red cabbage juice into each well. If no color change occurs add 5 more drops. Record the color of each well in the chart below.

Day 2: Correlating cabbage juice color with pH measured using a computer interfaced probe.

1. Setup the computer interfaced probe as indicated by your instructor. Be sure to have a beaker of distilled water to rinse the probe between uses.

2. Following the directions given with the probe, calibrate the probe using the supplied buffer solutions with known pH.

3. Label 6 beakers 1-6 and use the same solutions in the same configuration as yesterday. Pour each solution to be tested into a small beaker. There should be enough liquid in each beaker so that the probe will be completely immersed. Record the readings for each substance in the chart below.

4. Add 10 drops of red cabbage indicator into the solutions and record the color change.

5. After completing the experiment, wash the probe with distilled water and return the electrode to the storage solution.

Analysis:

Day 1 Day 2

Solution # / Solution Name / pH solution
w/ pH paper / Color w/ cabbage juice / pH solution w/ probe / Color w/ cabbage juice
1
2
3
4
5
6

Follow-up:

What is the pH of a solution a measure of?

What is the concentration of H+ ions in a solution with a pH of 1?

Did the pH values obtained in day 1 agree with those in day 2?

Using the data compiled in this activity, what would be the color of a solution with a pH of 4 if red cabbage is added?

Do you see any pattern in the type of substances used and their pH?

Assessment:

Participation- Student is on task, working well with group. Instructor should not have to settle disputes between group members on how and who will complete the objectives of the exercise.

Lab Report- This includes data for day 1 and day 2.

Essay questions: Each student will submit their responses to the essay questions. Responses will be graded on completeness, thoughtfulness, grammar, punctuation, and spelling.

Lab Report and essay questions will be submitted on time. No late work will be accepted without a written excuse from a parent or doctor.

Participation in Data Collection ------30 pts

Lab Report ------30 pts

Essay Questions------40 pts

Total------100 pts

Measuring pH of Household Chemicals

Teacher Support Materials

Overview:

This two day activity should follow several days of instruction on acids and bases. The pH scale should also be introduced in terms of concentration of H+ and OH- ions. Students should know how to calculate the concentration of H+ ions in a solution given its pH. The second part of this experiment is dependent on the availability of computer interfaced probes. The procedure of this part should be expanded or supplemented accordingly. If probes are unavailable the second day may be omitted.

Teacher and Student Objectives:

· Use red cabbage juice as a pH indicator by recording its color change in various chemicals.

· Use pH paper to obtain a more accurate measure of pH, including a numerical value.

· Set up and calibrate a computer interfaced pH probe.

· Use pH probe to take an even more accurate pH measure.

· Compare results and correlate a pH scale for the red cabbage juice indicator.

· Give students real life examples of acids and bases.

· Introduce students to computer interfaced probes for future experiments.

Who’s Being Taught?

· High school chemistry 10-12 grade

· 20-25 students

· Groups of 2-3 students

· Students should be instructed on where to find the materials needed to complete this activity

How to Assess:

Participation- Student is on task, working well with group. Instructor should not have to settle disputes between group members on how and who will complete the objectives of the exercise.

Lab Report- This includes data for day 1 and day 2.

Essay questions: Each student will submit their responses to the essay questions. Responses will be graded on completeness, thoughtfulness, grammar, punctuation, and spelling.

Lab Report and essay questions will be submitted on time. No late work will be accepted without a written excuse from a parent or doctor.

Participation in Data Collection ------30 pts

Lab Report ------30 pts

Essay Questions------40 pts

Total------100 pts

Strengths of Exercise:

· Connects everyday substances to acid base chemistry.

· Gives students practice taking pH measurements with pH paper.