# Chem 151 Lab Practical Final

Transcription

1 # Chem 151 Lab Practical Final Pigments: Putting the color in paint. The Paleolithic hunters who painted the unsurpassed animal murals on the ceiling of the cave at Altamira had only rudimentary tools. Art is older than production for use, and play older than work. Man was shaped less by what he had to do than by what he did in playful moments. It is the child in man that is the source of his uniqueness and creativeness, and the playground is the optimal milieu for the unfolding of his capacities. - Eric Hoffer The art of making paint is ancient. It is quite probable that Neanderthals made the paints used in their cave paintings from naturally occurring pigments such as soot and clay. Renaissance artists made their own paints and often went to great lengths to find the right pigments. Today there are thousands of known dyes and pigments and many chemists are employed developing pigments for use in many different industries. Educational Objectives: This experiment is designed to test the student s # understanding of basic chemical principles presented in the course, # ability to perform basic laboratory operations, # general ability to works safely and efficiently in the lab, and # ability to write a suitable report. Experimental Objectives: A student who performs this experiment is asked to # identify a metal salt of a particular color by experimentation, # determine how to prepare a specific amount of that salt, # prepare a sample of the salt and # write a suitable report. Background A pigment is a colored material that can be used to impart color to other materials. It is essentially the same as a dye. Pigments and dyes are used in many different human endeavors. The textile and food industries are well known to make heavy use of colorings. Cosmetics and building materials are also major players in the use of coloring. There are many more obscure uses as well. Surgical sutures are colored blue so they can be easily seen against the generally red color of human tissues. 1 O

2 O PRACTICAL FINAL The focus for this experiment will be on pigments used in paints. A paint is a suspension of a pigment in a liquid binder. The mixture can be spread over a surface (known as the substrate) to provide the color of the pigment. The binder is designed to harden over time to ensure the pigment sticks to the substrate. For water colors the hardening occurs when the water evaporates. For oil paints the hardening is the result of a chemical reaction of components in the oil with oxygen from the air. These are just two of the many methods used to affix binders to a substrate. The characteristics of the paint are determined by the properties of the pigments and the binder. In addition to color such things as gloss, adhesion, coverage and brightness are important components of a paint. One particularly important property is the durability of the color. Whether or not the color will fade with time is dependent on the stability of the molecules. Changes in the molecular structure of the pigment will result in a change in the apparent color. For paints intended to last a long time, molecular stability is an important factor. The Problem Pollard s Paint World, Inc, a specialty paint manufacturing concern has been contracted by Weso Studios to make tubes of various colored oil-based paints. Your assignment is to develop a procedure for making the pigment to be used in one of the paints. Overview In order to successfully perform the experiment you will need to know how to predict the product of an inorganic reaction, how to quantitatively manipulate materials and how to properly measure mass and volume. The experiment can be divided into two challenges. 1. Determine which pigment you will make. 2. Make a projected g of the pigment and develop a procedure for making 1.0 kg batches of the pigment. Procedure 1. Identifying the pigment. Two solutions of cations and two of anions will be provided. You are to determine which pair of these solutions will produce a product suitable to be used as a pigment for your assigned color. 2. Preparing the pigment. Once you have identified which solutions to use you are to determine how much of each you will need to mix to produce g of the pigment. 3. Making the pigment. Test your procedure by attempting to make g of the pigment and seeing what you actually get. The following are pointers and suggestions. * The best container to use for mixing the solutions is a beaker. * The solutions should be mixed slowly. We recommend putting one solution in the beaker and starting to add the other dropwise and with mixing. After having added a couple of mls, proceed to add a few mls at a time. * The mixture should be allowed to sit, undisturbed, for 10 minutes before filtration. * Gravity filtration is the best way to separate the pigment. This should take about 15 minutes. * The pigment will need to be dried. The best way to do this is as follows. Set up a hot plate with a clay triangle on top. Turn the heat on to a setting of 5 to 6. Put the filter paper on a # 2

3 watch glass and put the watch glass on the clay triangle. It will take between 15 to 30 minutes to dry the product. SUNSCREENS O Your Report. For your report you are to consider that you are a member of a development team. Your task is to report back to the team on your assigned pigment color. Your report will need to include. 1. The identity of your pigment. 2. Your procedure for preparing the pigment. 3. The results of your trial run preparing the pigment. 4. Your proposed procedure for preparing the pigment in 1.0 kilogram batches. Figure 1. Drying the precipitate 3 O

4 CHEM 151 Final Practical Evaluation Grade: /40 p Your name: Your TA s name: Lab section: Date: Guiding questions: State the question or questions you are asked to answer in this experiment. /2 p Preliminary analysis: Present the results that allowed you to determine the combination of reactants needed to prepare your assigned pigment. Reactant 1 Reactant 2 State the chemical formula of each reactant and product, as well as the color of the precipitate for each combination of reactants. Write the formula and color of your pigment: Reactant 3 Reactant 4 /6p Write the balanced chemical equation for the reaction that will allow you to produce your pigment: /2 p Present the stoichiometric calculations and results needed to predict the volume of each reactant solution that should be used to produce 0.25 g of your assigned pigment: /4p

5 Your name: Lab section: Procedure: Briefly describe the procedure that you followed to synthesize your pigment. /4 p Results and calculations: State the mass of pigment that you produced and calculate the actual yield for your process. /4p Explanation: Explain the chemical process that led to the formation of your pigment. How was it formed? How did it formed? Draw a particulate representation of the process /6p

6 Your name: Lab section: Claims and evidence: Based on your results, describe what you will need to do to prepare 1.0 kg of you assigned pigment taking into account the actual yield of your process. Justify your claims. /6 p Final reflections: Analyze the feasibility of the process that you followed to manufacture your assigned pigment at a large scale. Propose at least one way to improve the process based on your results. /6 p