Materials Included In Kit

Additional Materials Required

Safety Precautions

Copper(II) sulfate is slightly toxic by ingestion. Proper personal protective equipment (PPE), such as gloves and safety goggles, should be worn at all times while working with chemicals. Please follow all normal laboratory safety guidelines.

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. Leftover malachite and acacia can be stored in labelled empty containers indefinitely for future use or can be thrown in the regular trash according to disposal method #26a. Excess linseed oil can be disposed down the drain without prior pretreatment in accordance with disposal method #26b.

Teacher Tips

• Use this activity to introduce or expand on the topic of stoichiometry by asking students to predict the ideal ratios of copper sulfate and sodium bicarbonate reactants to give the best yield of malachite. Or, provide students a limited amount of starting materials so that they will have to do stoichiometric calculations prior to mixing the reactants to avoid any waste of starting materials.
• For introductory students this activity can serve as a straightforward example of chemical and physical changes because a solid precipitate (of different composition than the starting materials) forms, a gas is evolved and color change occurs. These things happen regardless of how much starting materials is used. That is, the reaction is very forgiving. Even the most novice chemist will see that it is possible to synthesize an inorganic mineral by simple means.
• Many manipulations can be performed on the malachite to alter and improve its ability to mix with the binders. For example, the particle size can be reduced by crushing the powder with a gloved hand or in a mortar and pestle. Explain to students that reducing particle size generally leads to more homogeneous end solutions. Moreover, as particle size decreases there are more points of contact between the binder and malachite so that smoother, less grainy (or clumpy) paint results.
• We found that it is important to use a binder: malachite ratio that results in a mixture that has the consistency of standard oil-based paint. We found that using wet malachite did not produce better or worse results than using completely dry malachite. And so there is no need to wait for the malachite to dry to begin combining it with the various binders.
• If necessary, this lab can be carried out in a single, 50-minute class period. However, it is more ideal to give one period to a discussion of the inorganic chemistry behind the synthesis of malachite as well as the associated chemical changes, and the synthesis itself; and one period to the pairing of the malachite with binders and subsequent painting and judging.

Sample Data

Answers to Questions

1. Which binder gave the best results?

   We found that egg yolks performed as the best binder, particularly when mixed with enough malachite to make a slightly viscous, smooth (non-grainy) paint. The egg yolk:malachite paint applies smoothly to paper and dries with a nice, glossy finish.

2. Which binder gave the worst results?

   We had a more difficult time obtaining optimal results with the acacia powder and found that it dried leaving a sandy, rough finish.

3. What is the ideal ratio of malachite to binder?

   The best ratio seems to be 1 egg yolk for every 20 g of malachite. This is also dependent on how the malachite is treated prior to mixing. That is, breaking up the solid malachite into finer particles prior to mixing gives better results.

Introduction

Chemistry’s relationship with art blends quantitative judgement with qualitative judgement. For example, when applying chemical principles to the synthesis of paint, the chemicals (and amounts) chosen can be precisely controlled. However, the product of the reactions between the chemicals chosen in the various amounts, or the paint, might be visually appealing to some and repellant to others. This lab will challenge you to make the best, or most visually appealing paint possible. The winner, the Monet of the class, will be determined by collective taste, not unlike how artwork is judged in public forums.

Concepts

• Inorganic chemistry
• Chemical and physical changes
• Chemical reactions
• Materials chemistry
• Experimental design

Background

Inorganic minerals are typically composed of metal and oxygen atoms as well as carbon and hydrogen in many cases. They often form underground, in areas of high pressure and temperature and must be mined, or dug out, to access. The processes by which minerals form can be replicated in a laboratory by selecting appropriate chemicals for reaction. For example, the mineral malachite is produced by mixing aqueous copper(II) sulfate with sodium bicarbonate, two widely available ingredients, according to the following reaction:

2 CuSO₄(aq) + 4 NaHCO₃(s) → CuCO₃•Cu(OH)₂(s) + 3 CO₂(g) + H₂O(l) + 2 Na₂SO₄(aq)

Owing to its bright color and ability to adhere to surfaces when combined with various binding agents, malachite has been used throughout history as a pigment in paint. Of course, its use as a paint has likely always been dependent on the painter’s knowledge of chemistry and/or experimental design. That is, a painter without any knowledge of chemistry might try using malachite, owing to its color, as a paint once combined with any number of other substances meant to bind it to a surface. These sorts of determinations can be made by simple trial and error methods. In contrast, a painter with a deep knowledge of chemistry would be able to determine first how to make malachite and subsequently which substances to mix it with to achieve the best possible result, or the most beautiful paint.

That is just what you will do in this lab. You will be given a variety of chemicals and asked to design the “best” paint possible. So channel your inner chemist to first synthesize an inorganic mineral and then channel your inner Michelangelo, or Van Gogh, to transform that mineral into a beautiful paint and piece of art!

Materials

Safety Precautions

Copper(II) sulfate is slightly toxic by ingestion. Proper personal protective equipment (PPE), such as gloves and safety goggles, should be worn at all times while working with chemicals. Please follow all normal laboratory safety guidelines.

Procedure

1. Add about 25 mL of aqueous 1M copper(II) sulfate to a sandwich bag.
2. Add sodium bicarbonate incrementally to the bag until the evolution of CO₂, or the formation of obvious gas bubbles, does not occur. Mix the reactants following each addition of sodium bicarbonate by kneading the bag with gloved hands.
3. Use a spatula or plastic spoon to remove the blue solid (malachite) from the bag. Spread the solid into three separate piles on a paper towel to dry.
4. Once dry the solid can be combined with the binders for application, or painting, onto a surface.
5. Inquiry Challenge: Identify the binder: malachite composition that produces the best paint, as judged by your class!

Student Worksheet PDF

14102_Student1.pdf