Category: Summer Learning (page 2 of 2)

Fruits Gone Bad? Discover Enzymatic Browning

Introduction

Have you ever wondered why apple slices turn brown once you cut them or why a yellow banana gets dark spots over time? Both of these phenomena have the same cause: enzymatic browning triggered by an enzyme called polyphenol oxidase (PPO). In this activity, you will find out how this enzyme works by turning a banana from yellow to brown in just a matter of seconds. Then you will explore how you can keep your apple slices looking fresh!

Time: 45 minutes – 1 hour

Key Concepts: Biochemistry, Enzymes, Food

 

Materials

  • Banana (yellow with no brown spots)
  • Stove
  • Pot
  • Water
  • Timer
  • Adult helper
  • Apple
  • Cutting board
  • Knife
  • Lemon Juice
  • Distilled vinegar
  • Milk
  • An additional one to two bananas (optional)
  • Fridge (optional)
  • Tape (optional)
  • Other fruits and vegetables to test (optional)

 

Prep Work

  1. Fill a pot with tap water.
  2. With the help of an adult, place the pot on the stove and heat the water until boiling. Always use caution and adult help when working around very hot water.

Procedure

  1. Take one of your bananas and look closely at its peel to observe its color.
  2. Carefully dip the bottom third of the banana into the boiling water for 30 seconds. Question: What happens to the banana when you submerge it in hot water?
  3. After the 30 seconds remove the banana from the boiling water and observe it for another three minutes. Question: What do you notice? Does the banana look different after a while? How?
  4. When the banana has cooled down peel the banana. Look at the fruit that was inside the peel. Question: Did you expect the banana to look like that?
  5. With the help of an adult cut two slices from the apple on a cutting board. Place each slice onto its side.
  6. Poke one of the apple slices with a fork several times. Then observe both slices for 15 to 20 minutes. Question: How do the apple slices change over time? Do you notice a difference between the two slices? If yes, can you explain why?
  7. Cut five more slices from the apple and place each slice on its side. Immediately after cutting, sprinkle milk on top of the first slice, distilled vinegar on the second slice, lemon juice on the third slice and water on the fourth slice. Keep the last slice as is. Then poke each apple slice several times with a fork.
  8. Observe all five apple slices for another 15–20 minutes. Question: How are the apple slices different after 15–20 minutes? What did each liquid do to the apple slice? Can you explain your results?

What Happened?

Were you able to change the color of your banana? Most likely, yes! You probably didn’t observe a big difference in the banana right after putting it into the boiled water, but within the next 30 seconds and after taking it out of the water it should have turned pretty dark. You should have noticed that the color change only happened where the banana was submerged in the hot water. This is because the boiling water caused heat stress to the cells in the outer layers of the banana peel and destroyed them. As the cells broke open, they released PPO and phenolic compounds, which then reacted with the oxygen of the air to form melanin. Only the peel should have been affected by enzymatic browning as the inner part of the banana was protected by the peel.

If you put a banana in the fridge, the whole banana should have turned brown. As the banana is a tropical fruit, it is evolved for warm temperatures, which is why the banana cells get damaged in the cold. If you taped parts of the banana, however, you should have noticed that underneath the tape the banana kept its yellow color. This is because the tape sealed the banana from the oxygen, which is necessary for the enzymatic browning reaction to happen.

When you cut an apple its tissue is damaged, and its cells are broken due to mechanical stress. This again triggers enzymatic browning, which you should have observed on the apple slices. When poking the apple slices with a fork, you damaged even more cells and released more enzyme and phenolic compounds, which is why this apple slice should have turned noticeably darker. The PPO content inside a fruit or vegetable determines the degree of its enzymatic browning. This is why some fruits or vegetables, even different types of apples that contain more of these compounds, become darker than others.

When you sprinkled, milk, lemon juice, vinegar, and water over your apple slices you should have noticed that acidic solutions such lemon juice prevented enzymatic browning. This is because PPO oxidase doesn’t work well in acidic environments, which means that the enzyme stops working or slows down considerably. So next time you eat an apple and don’t want it to get brown you know what to do!

Credits

Svenja Lohner, PhD, Science Buddies

Is the Egg Raw or Cooked? That is the Question!

Introduction

Have you ever found an egg in your refrigerator and wondered if it was cooked? Although eggs drastically change inside their shells when cooked, it is still remarkably difficult to distinguish a cooked egg from a raw one without cracking it open. In this activity, you will find out how physics can help you tell the difference!

Time: 45 minutes to 1 hour

Key Concepts: Solid, liquid, rotation
Materials
  • At least six chicken eggs similar in size and color
  • Saucepan
  • Stove (Use caution and ask an adult to help you use the stove and handle hot items in this activity.)
  • Water
  • Timer
  • Slotted spoon
  • Pencil
  • Two small plates
  • Sheet of paper
Prep Work
  1. Place three eggs in the saucepan. Add enough water so there is half an inch covering the eggs. Put the saucepan on the stove.
  2. Heat the water until it comes to a rapid boil and keep it boiling for seven minutes.
  3. Turn off the heat.
  4. Use the slotted spoon to take one egg at a time out of the hot water, rinse it under running cold water (optional), and store it in a safe place where it can cool completely.
  5. Use a pencil to make a small mark on the three raw eggs. Keep the mark subtle, as this will make it easier to test your ideas in an unbiased way.
  6. Store the raw eggs together with the cooked ones. This ensures that all eggs are at the same temperature when you start experimenting.

 

Step 5

Procedure

  1. Choose a raw egg and crack it open on a plate. Question: How does the content of the raw egg look?
  2. Repeat the first step with a cooked egg. Question:How does the content of a cooked egg differ from that of a raw egg?
  3. The goal of this activity is to find a test that can identify whether an egg is cooked or raw without cracking the shell. Question: What are your ideas?
  4. Choose one cooked and one raw egg from the four uncracked eggs that are left. Put the other pair of eggs aside for now.
  5. If you find a difference, note it on your sheet of paper. Remember there is a mark on the raw egg. This will help you identify which type shows a particular characteristic.
  6. Look at the eggs, smell them, and weigh them in your hands. Question: Does one look different, smell different, or seem heavier than the other?
  7. Gently tap your pencil against the cooked and raw egg and listen. Question: Can you hear a difference?
  8. Shake the eggs one at a time close to your ear. Question: Can you hear which one is raw?
  9. Put one egg on its tip and spin it. Lay it flat and spin it. Try it a few times before switching to the other egg. Question: Does one spin more easily than the other?
  10. Perform any other test or look for any other distinguishing characteristics you can think of.
  11. Review your notes. Question: Did you find differences? If so, do you think this difference appears because one of the eggs is cooked and the other is not? Why or why not?
  12. If you found one or several differences between the raw and cooked egg, test if these differences also appear in your last pair of eggs. Try not to look at the little mark on the raw egg while doing the test. Question: Does this difference distinguish the raw from the cooked egg in this pair, too? If you found a difference that held up for both pairs, do you think it can differentiate all cooked eggs from raw eggs? Why do you think the differences occur?

What Happened?

Did you notice that the inside of a raw egg is liquid, while the inside of a cooked egg is solid? It was probably impossible to tell the difference without cracking the shell until you tried to spin the egg. Even though it is difficult to spin a cooked egg, spinning a raw egg was probably much harder. This is expected.

When you boil an egg, the inside becomes solid. It does not change how the egg looks or its odor, so you cannot see or smell the difference. Shaking a raw egg does not make a sloshing sound because the liquid in the egg is contained in a membrane and only a small air bubble is present. Neither egg is hollow, so tapping it does not produce a clear audible difference.

You can tell the difference between a cooked and a raw egg by spinning it: a cooked egg is easier to spin. As the inside of a cooked egg is solid, the particles inside cannot move around relative to each other or the shell. The whole egg moves in unison. When you spin the cooked egg by twisting its shell, the hole inside moves along with the shell. In a raw egg, the inside is still liquid. The particles that make up the liquid can slide and move around relative to each other and the shell. When you spin the shell of the raw egg, the liquid inside does not start spinning right away—it needs some time to “catch up,” and friction between the shell and the liquid slows down the spinning motion. Since it is easier to balance an egg on its tip by spinning it faster, this also makes cooked eggs easier to balance than raw eggs. It also helps that the inside of the cooked egg is less wobbly since it does not move around (its center of mass is fixed).

Credits
Sabine De Brabandere, PhD, Science Buddies

Solubility Science: How Much is Too Much?

Introduction

Have you ever added a spoon of sugar to your tea and wondered why it disappeared? Where did it go? The sugar did not actually disappear—it changed from its solid form into a dissolved form in a process called chemical dissolution. The result is a tea-sugar mixture in which individual sugar molecules become uniformly distributed in the tea. But what happens if you increase the amount of sugar that you add to your tea? Does it still dissolve? In this science activity, you will find out how much of a compound is too much to dissolve.

Time: 20-30 minutes

Key Concepts: Chemistry, property of matter, solutions, solubility

 

Materials

  • Distilled water, found in the bottled water section of grocery stores.
    Note: You can also use tap water. However, as tap water contains additional ions that have been removed in distilled water, your solubility values may not match the published solubility values.
  • Materials

    Measuring cup

  • Glasses or cups, 8 oz. (8)
  • Spoons (4)
  • Measuring spoon (1 teaspoon)
  • Epsom salt (150 g)
  • Table salt (50 g)
  • Table sugar (cane sugar) (250 g)
  • Baking soda (20 g)
  • Scale
  • Marker
  • Paper
  • Pen
  • Optional: thermometer

Prep Work

  1. Using the marker, label two cups with each compound: “table salt,” “table sugar,” “baking soda,” and “Epsom salt.”
  2. Into one “baking soda” cup, measure 20 grams of baking soda.
  3. Into one “table salt” cup, measure 50 grams of salt.
  4. Into one “table sugar” cup, measure 250 grams of sugar.
  5. Into one “Epsom salt” cup, measure 150 grams of Epsom salt.
  6. Weigh each cup and write down their masses for each one.
  7. Add 100 mL of distilled water to each of the remaining cups. Use the measuring cup to make sure each cup has the same amount of water. The water should be at room temperature and the same for all cups. You can use a thermometer to verify that.

Proceedure

  1. Take both of the cups you labeled with “baking soda.” With the measuring spoon, carefully add one teaspoon of baking soda to the 100 mL of distilled water.
  2. Stir with a clean spoon until all the baking soda has dissolved. Question: What did you notice when you stir the solution with baking soda?
  3. Keep adding one teaspoon of baking soda to the water and stirring each time, until the baking soda does not dissolve anymore. Question: How does the solution look when the baking soda does not dissolve anymore?
  4. Repeat steps 1–3 with both cups labeled “Epsom salt.” Question: At what point does the Epsom salt solution become saturated?
  5. Repeat steps 1–3 with the table salt. Question: How many teaspoons of table salt can you dissolve in 100 milliliters of water?
  6. Repeat steps 1–3 with the sugar. Question: Could you add more or less sugar compared to the other compounds?
  7. Put each of the cups containing the remaining solids onto the scale and write down the mass of each one.
  8. Subtract the measured mass from your initial mass (see Preparation) for each compound. Question: What does the difference in mass tell you about the solubilities of each of the compounds? Which compound is the most or least soluble in distilled water?

What happened?

Did all of your tested compounds dissolve in distilled water? They should have—but to different extents. Water, in general, is a very good solvent and is able to dissolve lots of different compounds. This is because it can interact with a lot of different molecules. You should have noticed that sugar had the highest solubility of all your tested compounds (sucrose: about 200 grams per 100 mL of water), followed by Epsom salt (Magnesium sulfate heptahydrate: 113 grams/100 mL), table salt (NaCl: 35.17 g/100 mL), and baking soda (NaHCO3: 9.6 g/100 mL).

This is because each of these compounds has different chemical and physical properties based on their different molecular structures. They are all made of different chemical elements and have been formed by different types of bonding between these. Depending on this structure, it is more or less difficult for the water molecules to break these bonds and form new bonds with the solute molecules to dissolve them.

Credit

Svenja Lohner, PhD, Science Buddies

Make an Alka-Seltzer Powered Lava Lamp

Introduction

Have you ever seen a lava lamp? They were the height of 1960’s “groovy” room decorations. A few minutes after turning it on, a lava lamp has blobs of colored liquid floating towards the top of the lamp and then drifting back down. Making an actual lava lamp that you plugin would require some effort and unusual supplies, but you can create a non-electric version in just a few minutes with the help of the fizzing power of Alka-Seltzer. In this activity, you can find out how to make your own Alka-Seltzer® lava lamp. How will changing the temperature of the ingredients change the behavior of the colorful blobs in your lava lamp?

Time 30-45 minutes

Key Concepts: lava lamp, chemical reactions, carbonation, temperature

 

Materials

  • Tall identical jars or bottles, such as empty, clear, plastic 1-liter or 2-liter bottles (2)
  • Knife
  • Cutting board
  • Timer or clock that shows seconds
  • Water
  • Food coloring
  • Vegetable oil (enough to fill the jars nearly full)
  • An Alka-Seltzer tablet. Only one tablet is needed for the activity, but having additional tablets can be fun if you wanted to repeat lava lamp action.
  • A way to make one jar hot and one cold, such as by using a large bowl filled with hot water and access to a refrigerator or freeze

Instructions

  1. To each jar or bottle, fill it with 1-2 inches of water, add 5 drops of food coloring, and then fill it at least three-quarters full with vegetable oil. Put the cap on tightly to avoid spills and leaks.
  2. Somehow make one of the prepared jars be hot and one be cold. For example, to make one hot you could let it sit in a large bowl of hot water, and to make one cold you could store it in a refrigerator or freezer. Be careful when handling hot water.
  3. While you are heating and cooling the jars, cut an Alka-Seltzer tablet into quarters. Only two-quarter pieces are needed for the activity, but having additional pieces can be fun if you wanted to repeat lava lamp action.
  4. Once one jar is hot and one is cold, get a timer or clock ready and drop a quarter of a tablet into the heated jar. Note that the tablet piece may take a moment to sink through the vegetable oil to reach the water, where it will react. Start timing as soon as the tablet piece reaches the water and starts reacting. Question: How long does it take the tablet to disappear? How vigorous are the bubbles?
  5. Now drop a quarter of a tablet in the cold jar. Time how long it takes the tablet to disappear this time. Question: How long does it take the tablet to disappear in the colder liquid?
  6. Think about how the two reactions looked. Question: Do you notice other differences in how the reaction happens in the colder liquid versus in the hotter liquid? Why do you think you got the results that you did?

What Happened?

The ingredients in Alka-Seltzer combine with water to form a gas called carbon dioxide. The oil and Alka-Seltzer do not combine in this way though. The Alka-Seltzer tablets sink through the vegetable oil until they reach the layer of colored water. There the Alka-Seltzer dissolves in the water and forms a gas called carbon dioxide. The gas is lighter than the water and oil, so it bubbles up, taking a bit of colored water with it as it moves through the oil layer. You should have seen those bubbles, looking like colorful blobs, float through the oil layer to the top of the jar. At the top the bubbles should have burst (releasing the carbon dioxide gas), and then the colorful blobs should have sunk back to the bottom (now without carbon dioxide gas). The effect should have been reminiscent of a lava lamp.

The chemical reaction that causes the carbon dioxide to form happens more quickly in warmer water. For this reason, you should have seen that the Alka-Seltzer tablet dissolved more quickly in the hot water, in approximately 20-30 seconds depending on the temperature. This should have resulted in lots of rapid bubbling and an energetic lava lamp display. In contrast, the Alka-Seltzer tablet in the cold water should have dissolved more slowly, with most of it should disappearing in the first two to three minutes, resulting in a calmer and longer-lasting lava lamp effect.

Credits

Teisha Rowland, PhD, Science Buddies

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