Color Change Chemistry; Exploring Acids and Bases in Liquids (Jackie Brady)

SED 542. Assignment 5 By: Jackie Brady

Title: Color Change Chemistry; Exploring Acids and Bases in Liquids

Principle(s) Investigated: List all principles that apply to this activity.

· Arrhenius Theory of Acids and Bases

· The Brønsted-Lowry Theory of Acids and Bases

· The Lewis Theory

Standards: Past in the appropriate California content standards.

Grade 8 Focus on Physical Sciences

5. Chemical reactions are processes in which atoms are rearranged into different combinations of molecules. As a basis for understanding this concept:

e. Students know how to determine whether a solution is acidic, basic, or neutral.

Grade 9 through 12 Chemistry

Acids and Bases

5. Acids, bases, and salts are three classes of compounds that form ions in water solutions. As a basis for understanding this concept:

a. Students know the observable properties of acids, bases, and salt solutions.

b. Students know acids are hydrogen-ion-donating and bases are hydrogen-ion-accepting substances.

d. Students know how to use the pH scale to characterize acid and base solutions.

Materials: (Click on hyperlink to see where material can be purchased)

• Phenolphthalein Solution (pH indicator)

• Sodium Carbonate Solution (washing soda)

• Vinegar

• 3 glasses/beakers

• Something to stir solution

• See-through pitcher of water

Procedure: Give a detailed explanation of the procedure and include diagrams if possible.

1. In the first glass put a little less than 1/8 teaspoon of sodium carbonate, in the second put 6 drops of phenolphthalein solution, and in the third put three droppers-full of vinegar.

2. Add a few drops of water to the first glass and stir to dissolve the sodium carbonate.

3. Fill up the pitcher with tap water.

4. Fill each beaker with the about 200mL water from the pitcher.

a. “To prove that there is really just water in this pitcher, I am going to pour some in each of these beakers.” Students will notice that all four of the beakers remain clear with “water” when the water is poured in.

5. Pour all of them back in the pitcher except for the glass with the vinegar (the water will turn pink once the beaker with the phenolphthalein is added).

a. “Wow! We have gone from clear water to bright pink liquid. A transformation has happened!”

6. Refill the three glasses with water- the water will be pink.

7. Now pour all four glasses back in the pitcher. Refill the glasses one last time - the liquid will be colorless again!

Student prior knowledge: What prior concepts do students need to understand this activity?

Students should understand what an acid and a base are and the differences between the two. Students should know that pH is the negative log of hydrogen ion concentration in a water-based solution. They should know that the pH scale is a logarithmic scale that runs from 0 to 14 where 7 is neutral (pure water). Anything that has a pH below 7 is considered an acid and anything that has a pH above 7 is considered a base. Students should know that each number on the pH scale is ten times more or less acidic than the number above or below it. For example, something with a pH of 4 is ten times more acidic than something with a pH of 5 and 100 times more acidic than something with a pH of 6. A strong acid would have a pH of 1 or 2 while a strong base would have a pH of 13 or 14.

Students should know that a solution must be aqueous (water-based) in order to have a pH. Oils and other non-aqueous liquids cannot have a pH.

Explanation: Give a thorough explanation of the experiment or demonstration. Your explanation should be written to give your fellow teachers a solid understanding and include greater detail than what you might provide for your secondary students. Make certain to include equations whenever pertinent.

The trick to this experiment is pH or potenz (power) hydrogen.

In the first beaker I put a little bit of dissolved sodium carbonate, which is a base. In the second beaker I put a few drops of phenolphthalein solution, which is an indicator that turns pink in the presence of bases and colorless in the presence of acids.

The reason why this beaker didn’t turn pink right away the first time the water was poured in it is because it only turns pink in reaction to a base. Water is not a base nor acid, it is neutral. If you looked carefully, you would have noticed that when I poured the first beaker (the one with the sodium carbonate) back in the pitcher nothing happened to the color of the water. Then, when I poured the second beaker back into the pitcher (the beaker with phenolphthalein solution) the water instantly turned pink.

After this, I poured the third beaker into the water and the water remained pink. Notice how I didn’t pour the fourth beaker back into the pitcher just yet.

Next, I poured the pink liquid back into the three beakers and then back into the pitcher along with the fourth beaker (the beaker with a few drops of vinegar). Once the vinegar came into contact with the pink phenolphthalein water solution, it reacted and turned everything clear again.

In the fourth beaker I had a few droops of vinegar, which is an acid. So when I poured the first three beakers back into the pitcher, the sodium carbonate reacted to the phenolphthalein solution to turn all of the liquid pink. Then when I poured all of the beakers back in, the vinegar in the fourth beaker, lowered the pH to turn the phenolphthalein colorless again.

Like the universal indicator, phenolphthalein is a pH indicator, but it only turns colors in reaction to bases. When you poured the four glasses back into the pitcher, the phenolphthalein reacted to the sodium carbonate, a base, and turned the solution to red "kool-aid." To change it back to "water," all you had to do was add the acidic vinegar, which turned the phenolphthalein colorless again.

Questions & Answers: Give three thought-provoking questions and provide detailed answers.

1. Based on what we just discovered, list three household items that you think are acids and three that you think are bases.

a. Acids: Vinegar, lemon juice, sulfuric acid, urine, oranges, hydrochloric acid

b. Bases: Bleach, soap, ammonia, toothpaste, laundry detergent

2. What can you hypothesize that will happen if you mix an equal acid with an equal base? (Ex. Mixing a strong acid with a strong base)?

a. Essentially, the two chemicals cancel each other out and produce a salt and water. Mixing equal amounts of a strong acid and a strong base also produces a neutral pH (pH=7) solution.

i. An example of this would be mixing hydrochloric acid (HCl strong acid) with sodium hydroxide (NaOH strong base) to make table salt or NaCl.

3. Name an instance in real life where acids and bases are vital for humans or animals?

a. The stomach of vultures is so acidic that it can kill harmful disease and bacteria in dead animals.

b. The human stomach secretes hydrochloric acid to help break down and digest food.

c. The pancreas secrets a fluid rich in bicarbonate to neutralize stomach acid before it reaches the small intestine.

Applications to Everyday Life: Explain (don't just list) three instances where this principle can be used to explain other phenomenon.

1. pH is critical in maintaining healthy bodies. Staying hydrated and eliminating toxins maintain a neutral pH in the body. Antacids such as Pepto Bismol and Tums, relieve symptoms of acidity such as heart burn and nausea keeping a steady stomach pH.

2. Using toothpaste prevents tooth decay caused by excess acidity in the mouth.

3. Soil pH is critical in determining whether certain plants can grow in it or not.

4. Pools and Jacuzzis must maintain a certain pH to prevent algae formation and keep it clean.

5. In the food industry, most ingredients must maintain a specific pH in order for the food to turn out right. For example, food coloring in cookies.

Photographs: Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.

References:

https://www.khanacademy.org/science/chemistry/acids-and-bases-topic

http://chemwiki.ucdavis.edu/Core/Physical_Chemistry/Acids_and_Bases/Acid

Videos: Include links to videos posted on the web that relate to your activity. These can be videos you have made or ones others have made.

Allow MIT student Tyler DeWitt to teach you all about acids and bases through visuals and easy to understand explanations!

https://www.youtubcleare.com/watch?v=ujkuW-0cpNw&spfreload=10