Eyeball It2 Rounded Tablespoons Follow The Instru
INSTRUCTIONS: (also in the attached file)
There are two parts to this week’s activity.
Part 1. Acids and bases – a lab experiment
You will need:
- A head of red cabbage, shredded (you can shred/chop it yourself)
- Baking soda mixed with water (2 tablespoons baking soda in ¼ cup water) or ammonia cleaner if you have it
- Vinegar or lemon or lime juice
- Other substances around the house, like shampoo, toothpaste, orange juice, drain cleaner – it can be anything you want to test
- 3 bowls
Red cabbage contains pigments called anthocyanins which can indicate whether it is in contact with an acid (like vinegar) or a base (like baking soda) based on color changes. It can also show how strong an acid or a base a substance is.
How does it do this?
Chemists use the pH scale to express how acidic (like an acid) or basic (like a base) a substance is. A pH value below 7 means that a substance is acidic, and the smaller the number, the more acidic it is. A pH value above 7 means that a substance is basic, and the larger the number, the more basic it is. Red cabbage extract can tell us the approximate pH because it has different colors at different pH values (which were observed by someone with a pH meter).
These colors and approximate pH values are:
|
approximate pH: |
2 |
4 |
6 |
8 |
10 |
12 |
|
color of extract: |
red |
purple |
violet |
blue |
blue-green |
green |
Obtain some red cabbage and chop it up, if it’s not already shredded.
- Put a few strands in each of three bowls (enough pieces for you to see any changes which may occur).
- To one bowl, just add a little water. (Why add water? Think of Activity 1 and variables versus controls. 0.5pt)
- To the second bowl, add 1-2 tablespoons of vinegar (or your acid of choice) and stir. This is sample A in the data table.
- To the third bowl, add 1-2 tablespoons of baking soda solution (or ammonia). This is sample B in the data table.
- Record the color you see in each bowl and estimate its pH. Record these data in a data table (notebook). (1.5pt)
- Clean out the bowls. Does the bowl that had baking soda (or ammonia) in it feel different to your skin than the other bowls? If so, describe. (0.5pt)
- Put the three bowls out again. Place a few strands of shredded red cabbage in each.
- Find three different household materials (collect samples). You can even use saliva if you want! I recommend Windex, shampoo, milk, fruit juice, tomato, draino… it can be anything. Add one of the household items to each of the cabbage bowls to test for its pH. Record your data. (1.5pt)
- What conclusions can you make about whether your items are acidic, basic or neutral? (1pt)
- Take the left over baking soda (if you have any) and add about 1-2 tablespoons of vinegar directly to it. Or take vinegar and add a small spoonful of baking soda to it. What do you observe? Is this evidence for a chemical reaction? If so, what is the new substance being formed? (1pt)
Part 2. Maillard or Carmelization or Enzymatic browning reactions?
Now, what to do with all the left over cabbage you have?
I found a recipe that incorporates our lesson this week in acids and bases and the browning reactions. It is Rachael Ray’s Sauteed Red Cabbage recipe (Links to an external site.).
I have been pretty lenient about what experiments you do in terms of cooking something you want to eat. This time, I want you to try this recipe, and if you dislike it, then try giving it away to friends and family!
Ingredients:
- 2 tablespoons extra-virgin olive oil
- 1 small onion, sliced
- 1/2 red cabbage, shredded (you can use left over/untouched cabbage from Part 1)
- 1/3 cup white or apple cider vinegar, eyeball it
- 2 rounded tablespoons sugar
- 1 teaspoon mustard seed (I didn’t have mustard seed, so I just left it out and it turned out fine.)
- Salt and pepper
Directions:
Heat a skillet over medium high heat. Add oil and onion and saute 2 minutes. Add cabbage and turn in pan, sauteing it until it wilts, 3 to 5 minutes. Add vinegar to the pan and turn the cabbage in it. Sprinkle sugar over the cabbage and turn again. Season with mustard seed, salt and pepper and reduce heat a bit. Let cabbage continue to cook 10 minutes or until ready to serve, stirring occasionally. Recipe courtesy of Rachael Ray
As you make this recipe, think about the chemistry of acids and bases, as well as browning reactions.
1. Sautéing onions changes their color, texture and flavor. What kind of browning reactions are involved? Explain your choice. (Hint: Onions are 90% carbohydrates and 8% proteins) (2pt)
2. Take a “before vinegar is added” and “after vinegar is added” picture of your cabbage being cooked. What differences do you see and what is the chemical explanation for it? (2pt)