This report describes the creation of five pigments using chemical reactions. Three of these reactions were metathesis or double-replacement reactions, where an element or radical in one compound exchanges places with another element or radical in a different compound (Webster). The remaining two pigments were formed through neutralization reactions, which take place when an acid reacts with a base to generate salt and water (Webster).
Both types of reactions involve the combination of two substances to create a new solution. The metathesis reaction results in the formation of a solution and a precipitate, whereas the neutralization reaction produces water, salt, and carbon dioxide. These precipitates are considered pigments. When these pigments are mixed with a paint binding agent, they create paint. Pigment paints have been used since ancient times, such as in cave drawings, as a means of recording history. In the past, paint binders typically consisted of watercolors, which were created by mixing water with pigments and animal fat.
Modern water paintings tend to fade over time, whereas old cave paintings have retained their color. Over the years, the binders used in paintings evolved to meet the increasing demand. Gum arabic and honey are examples of binders that were developed to create long-lasting watercolors. These binders help maintain the color consistency and thickness of the watercolors. Another type of paint called casein was later discovered, primarily found in Egyptian paintings. Casein is a protein found in milk, which serves as a suitable binder for painting surfaces like canvases and walls (DBClemons).
Egg tempera paint was commonly used in Colonial America for painting sets for theatre and opera productions. Its dull sheen surface made it ideal for use under bright light (DBClemons). Acrylic paint, on the other hand, is composed of a precipitate, water, and an acrylic polymer that binds everything together. It is highly sought after due to its ability to resist water after drying (Upson) and its glossy and shiny result compared to other paints. Despite the popularity of acrylics and other types of paint mentioned earlier, egg tempera paint is not as widely recognized.
According to Douma, during the renaissance in the mid-fifteenth and sixteenth century, egg tempura paint was replaced by oils. Egg tempura paint is made by combining the yolk of an egg, water, and pigment. The thickness of egg tempura paint creates a three dimensional effect. Traditional paintings often have a refined look. In this experiment, watercolor is being used as the paint. The hypothesis for this lab assumes that if the watercolor binder is mixed with the precipitates from the reactions, then the resulting mixture will be a thinner and lighter paint.
The experiment included the production of five distinct pigments. The initial pigment produced was Chrome Yellow, where the pH of the solution was assessed before preparing a blend of 0.5M sodium chromate and 0.5M zinc sulfate. Up to five drops of 6M sodium hydroxide were subsequently introduced to the solution. Afterwards, the liquid was filtered to separate it from the precipitate, which was set aside for future utilization.
Following that, Barium White pigment was created by adding one milliliter of sodium sulfate to a test tube and documenting its color.
Afterwards, the test tube was added with 1 mL of barium chloride and then subjected to centrifugation in order to separate the liquid from the precipitate. The transparent liquid was poured off while the precipitate was transferred onto filter paper for storage. The subsequent pigments, synthetic Malachite, were carried out using a beaker to quantify 5 mL of a 0.5M copper sulfate solution, which was subsequently combined with 3 grams of sodium bicarbonate. Once the reaction ceased, the solution was split into two equal portions.
The first half of the solution was filtered and stored for the experiment’s completion, while the second half was left unfiltered for a week. In the following week, the unfiltered solution in the beaker underwent filtration and was set aside for another week. The fifth pigment used was Prussian blue.
A test tube was used to measure 1 milliliter of a 0.5 M solution of iron (III) chloride, which was then mixed with a 0.25 M solution of potassium ferrocyanide. The mixture was filtered and allowed to dry.
In the subsequent week, there were four options for paint binding: egg tempura, casein, acrylic, and watercolor or gum arabic.
This experiment employed watercolor as its medium. Initially, the pigment was ground with water to create a thick paste. Following this, gum Arabic was added in a 1:1 proportion. The outcomes revealed that when two solutions were combined, they underwent a reaction generating a pigmented or colored precipitate along with a liquid. Subsequently, the resultant precipitate could be fashioned into paint. In the case of the initial pigment, chrome yellow was produced. The combination of yellow sodium chromate and clear zinc sulfate yielded both an orange liquid and a yellow precipitate.
This is a metathesis reaction that results in the neutralization of the solution. The inclusion of sodium hydroxide causes an increase in the basicity of the solution. Following filtration, a yellow solid is formed. Crushing up the precipitate with gum Arabic produces yellow paint. The second pigment, barium white, initiates with clear sodium sulfate. Upon adding barium chloride, the solution becomes effervescent and generates a white precipitate. Centrifuging the solution yields a thick white paste at the bottom.
Once it dried, it turned into a white solid. Mixing gum Arabic, water, and pigment resulted in a white paint. Furthermore, a synthetic malachite was produced by adding sodium bicarbonate to copper sulfate, causing a chemical reaction that created a cloudy blue mixture. This reaction generated carbon dioxide, indicating it was a neutralization reaction. The solution was then divided into two equal parts. The first part was filtered and kept separately. After two weeks, the solid precipitate was combined with water and gum Arabic to create a watercolor paint.
The second half of the solution was kept in a beaker and became a precipitate after being dried. This precipitate was then mixed with water and gum arabic, resulting in a light blue watercolor pigment known as prussian blue. The formation of prussian blue involved a chemical reaction between iron (III) chloride and potassium ferrocyanide, which produced a blue solution and a dark colored precipitate. To complete the experiment, the solution was filtered and the precipitate was left to dry. After two weeks, the dried precipitate was added to the gum Arabic solution, creating a paint with an indigo color.
The watercolor paint is convenient for painting, but it has a tendency to spread on the paper. In discussing this issue, it was noted that the chemical reactions occurred as planned. In metathesis reactions, the positive and negative ions exchange partners and create different mixtures. The pigments that underwent the metathesis reaction included:
School bus yellow Na2CrO4 + ZnSO4 ZnCrO4 + Na2SO4
Barium white is formed by the reaction of BaCl2 and Na2SO4, which produces BaSO4 and 2NaCl.
When 4 moles of FeCl3 react with 3 moles of K4Fe(CN)6, they produce Fe4(Fe(CN)6)3 and also generate 12 moles of KCl.
The two acid-base reactions or double replacement
The equation CuSO4 + 2BaHCO3 produces CuCo3, Na2SO4, H2O, and CO2.
The presence of water, carbon dioxide, and a precipitate in the products indicates that this is a neutralization reaction.
The addition of the precipitates to the water and gum Arabic resulted in the expected outcome of a fluid-like consistency. The paint had a smooth texture and appeared thinner than other types of paint. Despite watercolor being the main form of communication in ancient times, it is not widely recognized in today’s world. Overall, the anticipated reactions, pigments, and use of gum Arabic yielded the desired results.
