chromatography

Separation Anxiety
Use water to learn about black magic…markers.
By using color chromatography—a technique that uses capillary action to separate different types of ink at different rates—you can discover the secret colors hidden in black ink.

Materials:

• Absorbent paper, such as a coffee filter or paper towel
• Scissors
• Water-based black marker
• Water
• Cup
• Optional: other water-based markers, permanent black marker, isopropyl alcohol

Assembly

Cut a strip of a coffee filter or paper towel about 2 inches (5 cm) wide and 6 inches (15 cm) long.

Use the water-based black marker to draw a line across the width of the strip. The line should be about 1 inch (2.5 cm) up from the bottom of the strip, running parallel to the paper’s bottom edge, with a small gap between the line and the edges.

Put enough water in the cup so that the level is 4-5 inches (10-13 cm) from the top of the cup.

To-Do and Notice

Place the end of the paper strip with the black mark in the cup and fold the other end over the cup’s edge so the strip doesn’t fall in. Make sure the bottom of the strip is in the water, but the black line is.

Watch as the water flows up the paper. When it reaches the black line, you’ll start to see some different colors moving up the paper strip.

Leave the paper in the water until the colors go all the way to the top edge. How many colors do you see?

If you have other water-based markers, try this experiment with them. Draw a line on a clean, dry coffee filter or paper towel strip. Put the paper in some freshwater and see what happens.

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What's Going On?

Most nonpermanent markers use inks that are made of colored pigments and water. When you use one to write on a dry coffee filter, the water in the ink transfers the pigment onto the paper. When the ink dries, the pigment remains on the paper.

Here, when you dip a marked-up paper strip in the water, the water travels up the paper due to a phenomenon called capillary action. When the water comes in contact with the dried ink pigments, they dissolve and get carried along with the water. Different-colored pigments are carried along at different rates: some travel farther and faster than others. The rate each pigment travels depends on the size of the molecule and how strongly it’s attracted to the paper. Since the water carries different pigments at different rates, the black ink separates to reveal the colors that were mixed to make it. This technique is called chromatography. The name comes from the Greek words chroma and graph for “color writing.” The technique was developed in 1901 by Russian botanist Mikhail Tsvet, who used it for separating the pigments that made up plant dyes.

There are many different types of chromatography. In all of them, a gas or liquid (like the water in your experiment) flows through a stationary substance (like your coffee filter). Since different ingredients in a mixture are carried along at different rates, they end up in different places. By examining where all the ingredients end up, scientists can figure out what was combined to make the mixture.

Why does mixing many colors of ink make black? Ink and paint absorb some of the colors in white light and reflect others. The reflected color is what you see. For example, green ink looks green because it reflects the green part of white light and absorbs all the other colors. Red ink looks red because it reflects red light and absorbs all the other colors. When you mix green, red, blue, and yellow ink, each ink that you add absorbs more light. That leaves less light to reflect to your eye. Since the mixture absorbs many colors of light and reflects very little, you end up with black.

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Going Further

What happens if you use a permanent black marker? Permanent marker inks do not dissolve in water, though some may dissolve in isopropyl or rubbing alcohol. Try different combinations of ink and liquid and see what happens.

Gassy Eggs

Eggsplore gas properties while making a Snack.

Discover properties of gases and learn about the anatomy of an egg by observing eggs cooked and cooled in different ways.

Materials:

Three raw eggs

Pot with lid

Stove or hotplate

Two containers large enough to hold one egg in a water bath

Water

Ice

Spoon (to remove cooked eggs from boiling water)

Knife

To-Do and Notice

Place all three eggs in a pot and cover them with water. Heat with the lid on until the water boils, and then turn the heat to low. Let the eggs cook for 12 minutes, then take them off the stove.

As the eggs are cooking, fill one container with ice and water to create an ice-water bath, and fill a second container with room-temperature water.

When fully cooked, place one egg in the ice-water bath, a second egg in the room-temperature water, and leave the last egg in the pot of hot water (off the stove).

Let all three eggs sit for 20 to 30 minutes. When they’re cool enough to handle, peel each one, taking careful notice of how they smell and how easy they are to peel.

Cut each egg in half. Is there a difference in how they look and smell based on how they were cooled?

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What's Going On?

Cooking is all about chemistry, and the familiar experience of boiling an egg can offer great illustrations of some of the properties of gases.

In this Snack, you may have noticed that the ice-cooled egg was the easiest to peel, followed by the room-temperature egg. That’s because of the egg’s internal structure.

Just inside the eggshell are two membranes that cause the egg to stick to its shell when dried out. In between these membranes is a little sac of air called an air cell. When this air cell is heated, the gas inside expands according to Charles’s Law, which states that the volume of a fixed amount of gas increases as its temperature increases. When the egg is rapidly cooled, the volume of the air cell decreases quickly, pulling the membrane away from the shell and making it easier to peel.

The opposite happens inside the egg that stays in the hot water, which cools gradually over a long period of time. When cooled slowly, the membrane stays attached to the egg, making the shell difficult to peel, even after it cools down. The size of the air cell increases as an egg age, so this effect is most dramatic with older eggs. Fresher eggs have smaller air cells, so maybe difficult to peel no matter how they’ve been cooked or cooled.

Once you peel and halve the eggs, you may notice that the slow-cooled egg has a greenish ring between the yolk and the white. The gray-green compound is iron sulfide, and that’s what’s responsible for the “eggy” odor of some hard-boiled eggs. Iron sulfide forms when hydrogen sulfide gas in the egg white reacts with iron compounds in the egg yolk. The solubility of a gas tends to decrease as temperature increases (think of a flat, warm soda versus a fizzy, cold soda that can keep more carbon dioxide in solution). Quickly cooling the egg keeps more of the hydrogen sulfide in the egg white: the gas doesn’t diffuse into the center, so it doesn’t react with the yolk. In the slow-cooled egg, which is warm throughout, the hydrogen sulfide is not as soluble in the white. It migrates to the yolk, where it reacts with iron, giving the egg yolks a green rim. The room-temperature egg should be somewhere in between.

The verdict: For easy-to-peel eggs with bright yellow yolks, use older eggs and try quickly cooling them in an ice-water bath after boiling.

Does your family have a favorite technique for boiling eggs? Tips and tricks for the best hard-cooked eggs include poking a hole in the egg before boiling, adding salt or baking soda to the water, and steaming instead of boiling. Try these out and see if you can determine if they improve the final result and if there’s a scientific explanation for why.

How often should you clean your dishwasher?

How often should you clean your dishwasher?
According to house-maintenance expert Bob Vila, you should clean your dishwasher filter and drain once a month. Fortunately, his three-step process is easy to do and doesn’t require any special tools.

How to clean your dishwasher:
Clear the drain: Remove the bottom dish rack. Inspect the dishwasher drain, removing any gunk or food caught there. This will improve drainage, increase cleaning efficiency and prevent damage to the dishwasher.


Put vinegar in the dishwasher: Start with an empty dishwasher. Place a cup of white vinegar in a dishwasher-safe container on the upper rack of the machine. Run the dishwasher through a hot-water cycle. This will wash away grease and grime and remove musty odors, too.


Baking soda rinse: Sprinkle one cup of baking soda across the bottom of the dishwasher. Run a short, hot water cycle. The dishwasher will be fresh-smelling and have a brightened, stain-free interior.


That's it, 3 easy steps.