Materials Included In Kit

Additional Materials Required

Prelab Preparation

Iron(II) ion solution: Prepare 48–72 hours in advance of the lab activity. Using scissors, cut a 2 x 2 cm piece of steel wool. Size is approximate—about 0.5–0.75 g. Measure 100 mL of vinegar into a 250-mL beaker and add the steel wool. Set the beaker aside where it will not be disturbed. After 48–72 hours, enough iron(II) ions will be produced in the solution. Remove the steel wool with beaker tongs and discard. Using a stirring rod, decant the solution into a clean beaker, leaving any residue of steel wool fibers in the original beaker for disposal (see Figure 1). The day of the lab, place another piece of steel wool in a clean 250-mL beaker with 100 mL of vinegar so students can observe the production of hydrogen gas. See Lab Hints for an alternative method.

Concentrated tea solution:Measure 100 mL of hot tap water into a 250-mL beaker. Add a tea bag to the hot water and let it steep for at least 10 minutes. Remove the bag with beaker tongs and discard. Let the tea cool to room temperature. The concentrated tea solution is rich in tannic acid. See Lab Hints for an alternative method.

Safety Precautions

While a 3% solution of hydrogen peroxide is very weak, it is an oxidizer and a skin and eye irritant. A small portion of the population finds acacia to be an allergen. Check with your students to see if such an allergy affects any of them. Steel wool is a flammable solid. Avoid contact with flames and electricity. Wear gloves to avoid splinters. The iron(III) tannate solution will stain clothing. Avoid contact of all chemicals with eyes and skin. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please consult current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The iron mixture made in this demonstration may be disposed of down the drain with plenty of excess water according to Flinn Suggested Disposal Method #26b.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. All parts of this laboratory activity can reasonably be completed in one 45-minute class period. The prelaboratory assignment should be completed before coming to the lab.
• The concentrated tea solution can be made ahead of time using room temperature water. Let the tea bag steep overnight. If made a day or more in advance, the tea should be refrigerated.
• The iron(II) solution can be produced in less than an hour by heating the vinegar and steel wool in the beaker on a hot plate. Heat to boiling and then reduce the heat and simmer for 7–10 minutes. Remove the beaker from the heat with beaker tongs or a hot vessel gripping device and place the beaker on a heat-resistant pad. Allow the solution to cool for a few minutes. Decant or filter the iron(II) solution. Collect the filtrate in a clean, 250-mL beaker and allow it to cool to room temperature.
• Since each group of students will need access to the chemicals used in this activity, placing small quantities, properly labeled, at several stations may expedite the process.
• The solid pigment [iron(III) tannate] produced is in the form of very fine particles which may be hard to identify as a precipitate. By letting the beaker of ink mixture sit undisturbed for a few minutes and then tipping the beaker slightly, students should be able to see the clear liquid as separate from the particles of black precipitate.
• Students should place the stirring rod on a paper towel after each use rather than leave the rod in the beaker. This will minimize the risk of tipping the beaker and spilling the ink.
• For students who may have difficulty controlling the micro-tip pipet, a plastic coffee stirrer with one end cut at an angle could be used as an alternative “quill.”
• This lab can be made more inquiry-based by having students adjust the amounts of the reactants—using more or less tea compared to the iron(III) solution, or adding the hydrogen peroxide as a last step, or even omitting the hydrogen peroxide. Students would test each mixture and compare results. More iron(II) solution and tea would be needed for these experiments.
• Ink made without hydrogen peroxide will be a lighter brown. Over time, however, the iron(II) ions will oxidize to form iron(III) and the ink will gradually appear darker.
• Students may wish to experiment with other types of paper such as filter paper, construction paper, or blotting paper. If more than one class period is needed for further experimentation, the ink mixture can be stored in bottles or jars with lids, such as Flinn’s polypropylene jars (AP4790). Be sure to label the bottles.

Teacher Tips

• This would be an excellent and easy activity to do as a science component for an interdisciplinary unit on medieval history or early American history.
• Students should have an understanding of ions and the difference between physical and chemical changes. The chemical reactions are given below, and teachers who have covered these concepts may decide to provide this information to the students. In the ink-making reactions in this activity, hydrogen ions from the vinegar react with the iron in the steel wool to produce iron(II) ions and hydrogen gas (Equation 1).
  {12576_Tips_Equation_1}
  The iron(II) ions (Fe²⁺) are then oxidized by reaction with hydrogen peroxide to form iron(III) ions (Fe³⁺) (Equation 2).
  {12576_Tips_Equation_2}
  Finally, the iron(III) ions react with tannic acid in the tea to form the black pigment, iron(III) tannate, which is insoluble in water.

Answers to Prelab Questions

1. Describe the safety hazards and precautions associated with the use of a 3% solution of hydrogen peroxide.

   Hydrogen peroxide can irritate the skin and eyes. Chemical splash goggles, chemical-resistant gloves, and a chemical-resistant apron should be worn. Hands should be washed thoroughly with soap and water before leaving the laboratory.

2. Why were oak galls used to make ink?

   Oak galls are a source of tannic acid.

3. What reasons can be inferred as to why tea will be used instead of oak galls in this activity?

   Oak galls need to be collected and crushed, mixed with water, and allowed to ferment for days or months. This is a lengthy process. Tea can be purchased at a grocery store and is quick and easy to make.

Sample Data

Part A. Properties of Iron(II) and Iron(III) Solutions

Part B. Making Ink

Answers to Questions

1. In Part A, hydrogen ions from the vinegar reacted with the iron in the steel wool to produce iron(II) ions. What evidence indicated that hydrogen gas was also produced in this chemical reaction?

   Bubbles were seen around the steel wool.

2. In Part A, the iron(II) ions reacted with hydrogen peroxide to produce iron(III) ions. Is this a physical or chemical change? Give evidence for your answer.

   The production of iron(III) ions is a chemical change. The solution changed color.

3. What was the purpose of adding acacia to the mixture? How much acacia seemed to work best in producing a smoothly flowing ink?

   The acacia thickens the ink and helps keep the pigment from settling to the bottom of the beaker. The optimal amount is usually 2.5–3 g per 10 mL of ink.

References

This activity was adapted from “An Iron-Clad Recipe for Ancient Ink,” ChemMatters, October, 2001.

Introduction

What if you had to make the ink you write with each day? Medieval scribes did just that, making what is known as iron-gall ink, the standard writing ink that was used in Europe for more than 700 years. Still used by some calligraphers today, iron-gall ink is produced by mixing tannic acid and an iron compound. Let’s re-create this medieval ink using a recipe similar to that used by Europeans during the Middle Ages.

Concepts

• Chemical reactions
• Chemical change
• Physical change

Background

The making of ink depends on chemical reactions. What is a chemical reaction? A chemical reaction takes place when substances combine or break apart to produce a new substance or substances with different properties than the original substance. A chemical reaction, also known as a chemical change, is different than a physical change, which occurs when matter changes state, size, or shape, but retains its identity. An example would be water boiling (changing from a liquid to a gaseous state). An example of a chemical reaction is oxygen in the air combining with iron to produce iron oxide, commonly known as rust. Oxygen and iron are the reactants and iron oxide is the product of the reaction. Many types of observable changes may be used to identify that a chemical reaction has occurred. Possible signs of chemical change include:

1. Formation of a solid precipitate upon mixing of two solutions.
2. Release of gas bubbles that are not due to a physical change.
3. A color change that does not result from dilution or color mixing.
4. A temperature change that is not caused by external heating or cooling.

Iron-gall ink is produced by reacting tannic acid with iron sulfate to produce iron tannate. During the Middle Ages, tannic acid was commonly obtained from oak galls, hence the name iron-gall ink. Oak galls are growths on tree leaves and stems caused by the egg-laying activities of gall wasps. As the female gall wasp lays her eggs, she punctures the twigs on young oak trees. After the eggs hatch, the larvae feed on the tree, secreting a chemical that irritates the tree, causing the tree to create a growth around each larva. This growth, or gall, is a source of food and protection for the developing wasp. When the larva becomes an adult, it chews its way out of the gall. The galls, rich in tannic acid, were collected and crushed, then mixed with water and allowed to ferment, anywhere from eight days to three months. During fermentation, the tannic acid is chemically changed by mold, producing gallic acid, resulting in a richer black color. Iron sulfate was then added to the fermented gall solution, producing the solid pigment known as iron(III) tannate, a product that is insoluble in water. Gum arabic (produced by the acacia tree) was then added to thicken the ink and keep the pigment suspended in the liquid. Without the acacia as a suspending agent, over time the pigment will settle to the bottom of the container.

No one knows who first thought to crush oak galls to obtain tannic acid, but the earliest record of a type of iron-gall pigment is from the first century A.D. Pliny the Elder (23–79) wrote about an experiment he did by dipping papyrus in tannic acid and then dripping an iron salt solution onto the papyrus. The papyrus turned black. By the 11th century A.D., medieval Europeans were making iron-gall ink and its use lasted for centuries. Leonardo da Vinci (1452–1519) wrote his notes with it, Johann Sebastian Bach (1685–1750) composed music with it, and the United States Constitution (1787) was drafted with it. This type of ink was preferred over carbon-based inks of earlier times because it did not smear on parchment (processed animal skin). The ink actually “ate into” the page by reacting with the collagen (a fibrous protein) in the parchment. Over time, the ink created holes in some documents. Preservationists who work with ancient manuscripts must deacidify such documents first and then remove any excess iron(II) compounds in order to keep the writings from being destroyed completely. This corrosive property of iron-gall ink led to its eventual disuse.

Experiment Overview

The purpose of this experiment is to explore the chemistry behind iron-gall ink by following a simple recipe to produce a similar type of ink. The ink will be made by mixing tannic acid from a concentrated tea solution (instead of oak galls) with a solution containing iron ions. The chemical reactions will be observed and the optimal amount of suspending agent (acacia) for a smoothly flowing ink will be investigated.

Materials

Prelab Questions

Read through the lab and answer the following questions on a separate sheet of paper.

1. Describe the safety hazards and precautions associated with using a 3% solution of hydrogen peroxide.
2. Why were oak galls used to make ink?
3. What reasons can be inferred as to why tea will be used instead of oak galls in this activity?

Safety Precautions

While a 3% solution of hydrogen peroxide is very weak, it is an oxidizer and a skin and eye irritant. A small portion of the population finds acacia to be an allergen. Please notify your instructor if such allergies affect you. Avoid contact of all chemicals with eyes and skin. The iron(III) tannate solution will stain clothing. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

Part A. Properties of Iron(II) and Iron(III) Solutions

1. Your teacher will show you a beaker containing vinegar and steel wool.
2. Observe the color and appearance of the mixture. Record your observations in the data table, in the row labeled Iron(II) Solution, including any evidence of a physical or chemical change taking place.
3. Steel wool reacts with vinegar to produce hydrogen gas and iron(II) ions (Fe²⁺). Using a graduated cylinder, measure 5 mL of an iron(II) solution prepared by the teacher.
4. Pour the iron(II) solution into a 100-mL beaker.
5. Using a thin stem pipet, draw a small amount of 3% hydrogen peroxide into the stem. Hold the pipet over the beaker containing the iron(II) solution. Do not allow the pipet to come in contact with the iron solution. Squeeze out 5 drops of the hydrogen peroxide into the iron solution. Expel any remaining hydrogen peroxide back into the original container.
6. Pick up the 100-mL beaker and gently swirl the contents, being careful to keep the solution in the beaker. Hydrogen peroxide reacts with iron(II) ions to produce iron(III) ions (Fe³⁺). Observe the color and appearance of the iron(III) solution. Record your observations in the data table in the row labeled Iron(III) Solution, including any evidence of a physical or chemical change taking place.

Part B. Making Ink

7. Using a clean graduated cylinder, measure 5 mL of concentrated tea solution.
8. Pour the tea into the beaker containing the iron(III) solution. Tannic acid from the tea reacts with iron(III) to produce iron(III) tannate. Observe the color and appearance of the mixture. Record your observations in the data table in the row labeled Iron(III) Tannate, including any evidence of a physical or chemical change. Let the solution sit undisturbed for a few minutes.
9. While the solution sits undisturbed, place a weighing dish on the balance.
10. Tare (zero) the balance.
11. Using a scoop or a spatula, measure 1 g of acacia in the weighing dish.
12. Disturbing the contents as little as possible, look closely at the beaker with the iron(III) tannate mixture again. Tip the beaker slightly. Do you notice a difference between the liquid and the pigment that indicates a chemical change? Record your observations in the Data Table in the row labeled Iron(III) Tannate.
13. Add 1 g of acacia to the iron(III) tannate mixture. This will thicken the ink and keep the pigment from settling to the bottom of the beaker.
14. Using a stirring rod, stir the mixture for one minute. If the acacia appears to “clump” or stick to the stirring rod, carefully scrape any acacia off the stirring rod into the beaker, let the suspension sit for a minute, and then stir again.
15. Remove the stirring rod from the beaker and place it on a paper towel.
16. Using the micro tip pipet for a “quill,” fill the pipet with the ink mixture.
17. Blot excess ink on a second paper towel so the outside of the pipet quill is clean.
18. Using a piece of notebook paper for practice, try writing your name with the ink. Squeeze the bulb of the micro tip pipet slightly to release a small amount of ink. Squeezing too hard will result in thick blotches of ink on the paper. Caution: The ink will stain clothing, so be sure the tip of the pipet is in contact with the paper before squeezing the bulb.
19. The ink will “bead up” on the notebook paper. If the ink takes too long to dry, use a paper towel to blot excess liquid from the notebook paper.
20. If the ink appears too thin and watery, measure and add 0.5 g of acacia to the ink mixture and repeat steps 14–19. Continue to add acacia, 0.5 g at a time, up to 2 more grams, until the ink is a desirable thickness. Caution: Adding too much acacia will prevent the ink from being easily drawn into the “quill.”
21. After adding the acacia to the ink mixture and testing the ink on paper, record your observations in that data table in the row labeled Iron(III) Tannate + Acacia, including any evidence of a physical or chemical change.
22. If the ink gets too thick, add concentrated tea, 1 mL at a time, to the ink mixture.
23. Once the ink is the right consistency and you can write your name, use the piece of chromatography paper provided to write a brief message or make a drawing. This paper is more like the parchment used in medieval times than the notebook paper.
24. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

12576_Student1.pdf