Chromatography

What colors make up black marker ink?

Difficulty:
Danger:
Duration:
20 minutes
Chromatography

Reagents

Safety

  • Put on protective gloves and eyewear.
  • Conduct the experiment on the plastic tray.
General safety rules
  • Do not allow chemicals to come into contact with the eyes or mouth.
  • Keep young children, animals and those not wearing eye protection away from the experimental area.
  • Store this experimental set out of reach of children under 12 years of age.
  • Clean all equipment after use.
  • Make sure that all containers are fully closed and properly stored after use.
  • Ensure that all empty containers are disposed of properly.
  • Do not use any equipment which has not been supplied with the set or recommended in the instructions for use.
  • Do not replace foodstuffs in original container. Dispose of immediately.
General first aid information
  • In case of eye contact: Wash out eye with plenty of water, holding eye open if necessary. Seek immediate medical advice.
  • If swallowed: Wash out mouth with water, drink some fresh water. Do not induce vomiting. Seek immediate medical advice.
  • In case of inhalation: Remove person to fresh air.
  • In case of skin contact and burns: Wash affected area with plenty of water for at least 10 minutes.
  • In case of doubt, seek medical advice without delay. Take the chemical and its container with you.
  • In case of injury always seek medical advice.
Advice for supervising adults
  • The incorrect use of chemicals can cause injury and damage to health. Only carry out those experiments which are listed in the instructions.
  • This experimental set is for use only by children over 12 years.
  • Because children’s abilities vary so much, even within age groups, supervising adults should exercise discretion as to which experiments are suitable and safe for them. The instructions should enable supervisors to assess any experiment to establish its suitability for a particular child.
  • The supervising adult should discuss the warnings and safety information with the child or children before commencing the experiments. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
  • The area surrounding the experiment should be kept clear of any obstructions and away from the storage of food. It should be well lit and ventilated and close to a water supply. A solid table with a heat resistant top should be provided
  • Substances in non-reclosable packaging should be used up (completely) during the course of one experiment, i.e. after opening the package.

FAQ and troubleshooting

Can I use my own black marker or markers with different colors?

We recommend trying this experiment with the marker in the set first. But in general, this experiment works for any marker containing a combination of various dyes. Try them out! Brown and blue markers will usually yield an interesting result. Check out purple and orange as well! Just keep in mind that the result can depend on the marker manufacturer.

I drew a circle larger than one centimeter. What should I do?

No worries! Just continue the experiment.

Will this experiment work without NaHSO4?

Yes, but the results will differ. Water won’t separate the colors quite as well — you will achieve the desired result, but not as distinctly as with a strong acid like sodium hydrogen sulfate NaHSO4.

The cotton cylinder fell over. What should I do?

Simply put it back as quickly as possible. Don’t consider this a failure! You can always repeat the experiment with a new piece of filter paper and reuse the wet cotton cylinder.

The cotton cylinder is very unstable.

It’s possible that you haven’t applied enough solution to the cylinder; try adding a little more.

10 minutes passed, and nothing happened. What should I do?

Try adding some more NaHSO4 solution to the cotton cylinder (10–20 drops).

I’ve run out of NaHSO4, how can I replace it?

You can try a solution of citric acid or baking soda NaHCO3. And, of course, you can try using water! It works more slowly and separates the dyes less effectively, but on the other hand, you can repeat the experiment using water as many times as you like.

I’ve run out of cotton cylinders. What should I do?

In this case, you can take a bundle of absorbents, pull out one cylinder, and use it.

Step-by-step instructions

A black marker is obviously filled with black ink. Or is it?

dyes-v2_chromatography_en_iks_01

Since the dye in the marker is water-soluble, we will perform our test using an aqueous solution. We will use a solution of sodium hydrogen sulfate NaHSO4, but other aqueous solutions or even clear water would also work to some extent.

dyes-v2_chromatography_en_iks_02

Our solvent dissolves the ink that the circle was drawn with and spreads through the filter paper, dragging the ink along with it. Let’s see what’s going to happen in this process.

dyes-v2_chromatography_en_iks_03

Disposal

Dispose of solid waste together with household garbage. Pour solutions down the sink and wash with an excess of water.

Scientific description

The black dot  disappears and becomes a series of brightly-colored rings , . How come? The liquid from our cotton cylinder spreads through the filter paper, dragging the ink along with it . In such circumstances, some compounds follow the flow of the liquid more readily, while others cling to the paper more tightly. This way, the compounds that ultimately move faster  can be separated from the ones that move more slowly . This method for the separation of compounds is called chromatography. And it turns out the black marker was filled not with one black dye, but with several colored dyes!

There are many ways to achieve black by mixing different dyes. This is also true for other colors. Try analyzing markers that you have at home!

You can also try and separate other mixtures using different solutions. For example, a mixture of thymol blue  and eosin  will separate well if you use a solution of Na2CO3 .

Why do the colors separate?

The ink in the black marker consists of several pigments dissolved in a solvent containing some water and alcohol. At the end of the experiment, we can see each of these separate pigments on the filter paper.

The black circle is moistened with sodium hydrogen sulfate NaHSO4, which gradually spreads along the paper. The pigments comprising the black ink move with the solution as well, but since these pigments are different in nature, they move at varying speeds. This results in multicolored rings!

How can a few colored dyes make black when mixed?

We should start with two key concepts: what is light, and what is color? Light is actually electromagnetic radiation. This is a rather complex topic, but mostly we need to understand that light is something that objects (and, for example, our eyes) can interact with. An object’s color is the result of such interactions.

We usually perceive light sources to be white light (take, for instance, sunlight, or light from a lamp). In reality, any more-or-less white light is a mixture of the whole spectrum of colored light.

There are two interactions between light and objects we need to consider: light absorption and light reflection. When an object reflects all the white light hitting it, our eyes perceive the object to be white. When an object absorbs all the light that hits it, we don’t see any reflected light from this object and it seems black.

dyes-v2_chromatography_sci_PIC2

Colored things like dyes, in turn, absorb some colors more than others, and as a result, we see some of the light reflected back. But this kind of object doesn’t look white — it can be red, blue, yellow, or a multitude of other colors!

dyes-v2_chromatography_sci_PIC3

And thus if we mix some differently-colored dyes, they can, together, absorb all the light hitting them, leaving our eyes without any reflected light from this mixture. In other words, a mixture of vividly-colored dyes can be black, just as in this experiment!

Is it important to draw the black circle in the middle of the paper sheet?

Yes; the dissolved dyes will spread along the paper evenly only if we start from the middle. Otherwise, the experiment will work, but differently, and it will be harder to evaluate the result. But you can always give it a try just to see what happens!

What do we need the NaHSO4 solution for?

Sodium hydrogen sulfate NaHSO4 is a substance that can make a solution very acidic. In other words, the pH of a solution containing NaHSO4 will be very low. As it turns out, the pigments in black ink separate more easily on the filter paper in acidic conditions.

The method of separating substances according to their interactions with the solution they move with and the surface they spread through is one of many types of chromatography.

Follow up

Want to conduct more experiments based on chromatography? Clean and dry the Petri dish. Then set it upside down on the tray and place a new sheet of filter paper on top. Drip some sodium carbonate Na2CO3 solution onto a new cotton cylinder. Stop when the solution starts dripping from the other end of the cylinder.

Deposit two drops of thymol blue solution onto the center of the filter paper. Add one drop of eosin solution right on top of thymol blue. Set the cylinder upright in the center of the spot on the filter paper. Wait for 5–10 minutes. Observe the result!

That's interesting!

More about mixture separation techniques:

Chromatography is not the only separation technique out there. The method used depends on the kind of mixture in question. For example, two or more liquids are usually separated via a method known as distillation, in which the components of a liquid mixture are vaporized, condensed, and isolated.

A mixture of liquid and solid components can be separated via evaporation, which involves heating the mixture until the liquid evaporates completely, leaving the solid compound behind. This technique is used to obtain marine table salt from seawater, utilizing the heat from the sun.

Filtration, yet another technique, is used to separate a pure insoluble solid from a liquid; the liquid is passed through the pores of a filter that the solid particles cannot penetrate. Depending on the size of the solid particles, filtration can be used for different purposes. Some filters are used to eliminate microbiological organisms such as bacteria, while others can remove only sand and soil. This method is widely applied in everyday life. For example, coffee is often prepared by passing hot water through ground coffee beans and a filter. Even your kidneys are an example of a biological filter!