NSF Research Experiences for Teachers RET

Transcription

1 NSF Research Experiences for Teachers RET Subject Grade Levels Crystallization H.S. Chemistry Essential Question *How do crystals grow? *How can we find the factors which affect the growth of the crystal? *Why do the crystals seem to stop growing? *How fast do the crystals grow? in a half a minute? A minute? More? *How large to they get? Science Objectives Students will understand and write crystallization process using the physical and chemical change of organic/inorganic compounds. LESSON ACTIVITIES Engage Students can see some of the pictures of crystals from old experiments or nature. While you show the pictures of crystals, teacher can start giving explanation of crystals. How do they form? Sometimes when a mineral is forming in the earth s crust, it grows into a particular geometric shape. The shape of a crystal results from the way the atoms or molecules of a mineral come together as the mineral is forming. So, each mineral has its own crystal shape. This solid body has a characteristic internal structure and is enclosed by symmetrically arranged plane surfaces, intersecting at definite and characteristic angles. Fashioned snowflakes, flawless diamonds with glittering facets, the almost perfect cubes of salt grains are all fine examples of crystals bodies with a pattern of flat surfaces that meet at definite angles. The universe is full of almost all nonliving substances in the solid state form crystals. Crystals are ice, snow, sugar, salt and sulfur; in metals like gold, silver, copper, iron and mercury; in precious stone like zircon, emerald, topaz, ruby, and sapphire the main purpose of crystallization in an organic chemistry procedure is to purify the desired compound. Crystallization also may be used to isolate a solid organic compound from a mixture of compounds in a step in the work-up of a reaction mixture ( &skin=l )

2 Explore Perform Screening organic/inorganic compounds to form crystals. Divide your class for at least 3 groups, and each group will use one kind of compound at a time. At the end of the experiment, let them to discuss with other groups about what they got at the end of experiment. Explain Elaborate 1. What methods are we using to grow crystals? 2. How are we monitoring the process? 3. How to draw a graph showing how the mass of the crystal has changed? 4. How to draw a second graph showing how the size has changed during time?. Investigate different minerals and their crystal shapes and colors. Research different crystal shapes and find examples of minerals with those shapes. Visit a local museum that features minerals. Use solubility graph question sheet to practice reading and interpreting graphs. Evaluate The students will learn and understand some knowledge about this crystallization experiment. How the students demonstrate their skills. What is the main purpose for this lesson? What are the helper tools to solve the problem? The experimental conclusion, a picture, a Power Point presentation, or any other tools? Materials Lab Safety Glasses Class Aprons Disposable gloves Lab Coat PET bottle Graduated cylinder two beakers paper to hold the chemical balance a burner or hot plate thermometer water chemical compound for the crystal thread wooden stirring stick for solution Assessment Products 1. Please discuss below questions at the end of an experiment.

3 A. What problems did you have during the project? How did you solve them? B. How did the solubility of your chemical change as the water was heated and then cooled? C. Under which conditions could your crystal become smaller while in the beaker of solution? D. Do all chemicals have crystals of the same shape? E. How would you improve what you have done in this project to produce a better crystal? INFORMATION FOR TEACHERS Chemistry Standards (2) Scientific processes. The student uses scientific methods to solve investigative questions. The student is expected to: (E) plan and implement investigative procedures, including asking questions, formulating testable hypotheses, and selecting equipment and technology, including graphing calculators, computers and probes, sufficient scientific glassware such as beakers, Erlenmeyer flasks, pipettes, graduated cylinders, volumetric flasks, safety goggles, and burettes, electronic balances, and an adequate supply of consumable chemicals; (F) collect data and make measurements with accuracy and precision; (G) express and manipulate chemical quantities using scientific conventions and mathematical procedures, including dimensional analysis, scientific notation, and significant figures; (H) organize, analyze, evaluate, make inferences, and predict trends from data; and (I) communicate valid conclusions supported by the data through methods such as lab reports, labeled drawings, graphs, journals, summaries, oral reports, and technology-based reports. (4) Science concepts. The student knows the characteristics of matter and can analyze the relationships between chemical and physical changes and properties. The student is expected to: (A) differentiate between physical and chemical changes and properties; (B) identify extensive and intensive properties; (C) compare solids, liquids, and gases in terms of compressibility, structure, shape, and volume; (D) Classify matter as pure substances or mixtures through investigation of their

4 properties. (7) Science concepts. The student knows how atoms form ionic, metallic, and covalent bonds. The student is expected to: Prior Student Learning (A) name ionic compounds containing main group or transition metals, covalent compounds, acids, and bases, using International Union of Pure and Applied Chemistry (IUPAC) nomenclature rules; (B) write the chemical formulas of common polyatomic ions, ionic compounds containing main group or transition metals, covalent compounds, acids, and bases; 1- Define : Crystallization Diffusion Compound Phase Change 2- What is meant by crystallization process? Give an example. Possible Prior Misconcepti ons Make sure that all students wearing goggles and lab coat for any lab incidents. Also, students need to be washing their hand before and after crystal experiment. This project has to be done at least 3 different groups. Teacher can do more groups. This lab can be done in one hour but the crystals can start grow more than one day. After first date of experiment, students can start to see some crystals grown nicely or not. If students cannot see any grown crystals, this is usually caused by a solution temperature above 40 degrees at the time that the crystal was added, water bath at a higher temperature than 40 degrees, too much water added to the solution or too little chemical. Sometimes, the students have tied the seed crystal too loosely and it fell to the bottom of the beaker. At the end of the crystal growing, a "beauty contest" can occur. Students can vote for "Most Beautiful", "Best Shape", "Most Sympathetic" crystal awards. Students can eat their rock candy crystals. The last recommendation is for the teacher to try this project ahead of time. In this way, sample crystals will available for students to see and there will be a supply of seed Crystals for students to use. Lesson Sequence How to grow Crystals using different compounds. Background Information Crystals are solids that form by a regular repeated pattern of molecules connecting together. In some solids, the arrangements of the building blocks (atoms and molecules) can

5 be random or very different throughout the material. In crystals, however, a collection of atoms called the Unit Cell is repeated in exactly the same arrangement over and over throughout the entire material. Because of this repetitive nature, crystals can take on strange and interesting looking forms, naturally. When we grow crystals we are separating all the building block molecules into individual units in water and letting them fall naturally into their appropriate place in the repetitive structure as the water evaporates. Through these pages you can learn what types of crystals there are, why different crystals have different shapes and sizes, find out how light affects the color of a crystal and how crystals form and how they grow. Making Crystal Gardens is fun and rewarding, so we've left you a few ideas along with other Crystal growing recipes you can try - such as growing Crystals on a String - that with a little patience and imagination you could suspend from the ceiling as a mobile! Please go to this web page for more detail information about crystals and crystallization. ( Adaptation s for Special Learners Extensions -Please work with them to demonstrate to others so these students can understand and enjoy with experiment. Don t let them to do all experiment by themselves. - When you leave your crystals in lab, don t bump them, don t swirling them. Otherwise, your crystals will mess up. - Make sure that the solvent is completely dissolved. If completely dissolved but there is still compound in solvent, filter them. - The purer the compound, the better your chance of growing single crystals. - Don't give up too quickly! Solvent choice is critical, and sometimes multiple solvents are needed for the molecules to pack. Just try everything and you'll find that you can almost always get a crystal. Resources 1-University of Houston. growing crystals. www. Atlantis.coe.uh.edu. 2005, June 2011< 2-Dinger, Maarten. Some Crystal Growing Tips , The Center for X-ray Crystallography. June 2011 < 3-Helmenstine, Anne Marie. How to Make Rock Candy < 4-Helmenstine, Anne Marie. How to Grow Great Crystals June < 5-Harrington, Jenny. Methods of Making Crystals for a Kids Science Experiment , June 2011 <

6 6-Kinder, Carolyn. Crystals: What Are They and What Holds Them Together , June 2011, < STUDENT HANDOUT [SECTIONS WILL VARY PER LESSON] Essential Question 1- How do crystals grow? 2- How can we find the factors which affect the growth of the crystal? 3- Why do the crystals seem to stop growing? 4- How fast do the crystals grow? in a half a minute? A minute? More? 5- How large to they get? Explore 1 st group compound is 25 grams of Copper Sulfate 2 nd group compound is 2 cups of Sucrose 3 rd group compound is 2.5 grams of Vanillin 1. Take the compound and measure it to use. 2. Measure out 50 ml of water with the graduated cylinder and pour it into a small beaker. 3. Add the compound (Copper Sulfate; Sucrose or Vanillin) to the water. Heat the mixture to 50 C while stirring with a non-metal stick to dissolve solute. When the solution is dissolved, take the beaker off the heat. 4. Make sure that the seed crystal (teacher can give you before experiment) is tied securely on a piece of thread. Attach the other end to the wooden splint. Find the mass of the seed crystal and measure its length. 5. Prepare a warm water bath by heating water in the big beaker to 40 degrees Celsius. Use about 150 ml of water for the water bath. 6. Put your seed crystal into the small beaker. 7. Put your seed crystal with its beaker of solution carefully into your water bath in big beaker. Leave the beakers in a safe place. 9. Next class, check if your crystals are growing or not. Ask your teacher if the crystals grew enough to take them and record their mass, shapes. 10. Every day (or when your teacher directs), check your crystal. Measure its length without touching crystals (ask the teacher to how to measure). At the end of experiment, take the crystals out of beakers and find its mass. Write at least two sentences about your observations in your journal. Keep a chart of the date, size and mass of your crystal.

7 Materials Lab Safety Glasses Class Aprons Disposable gloves Lab Coat PET bottle Graduated cylinder two beakers paper to hold the chemical balance a burner or hot plate thermometer water chemical compound for the crystal thread wooden stirring stick for solution Explain/Product 1. What methods are we using to grow crystals? 2. How are we monitoring the process? 3. How to draw a graph showing how the mass of the crystal has changed during time? 4. How to draw a second graph showing how the size has changed during time? Elaborate Investigate different minerals and their crystal shapes and colors. Research different crystal shapes and find examples of minerals with those shapes. Visit a local museum that features minerals. Use solubility graph question sheet to practice reading and interpreting graphs. Evaluate/Test, rubric, skill, etc. Assessment: 1. Please discuss below questions at the end of an experiment. A. What problems did you have during the project? How did you solve them? B. How did the solubility of your chemical change as the water was heated and then cooled? C. Under which conditions could your crystal become smaller while in the beaker of solution? Explain why each would happen and how you could "fix" each problem. D. Do all chemicals have crystals of the same shape? Suggest reasons to

8 explain why. E. How would you improve what you have done in this project to produce a better crystal? Teacher s Answer Key for Essential Questions 1- How do crystals grow? Crystals start growing with the help of some solid matter already in the solution. When the compound is a solid when it is pure, there will be some attractive force between these solute molecules. Most of the times when these solute molecules meet they will stay together for a little while, but then other forces will eventually pull them apart. However, once there is a certain number of solute molecules, which is considered a critical size, where the combined attractive forces between the solute molecules become stronger than the other forces in the solution that tend to disrupt the formation of these aggregates. Molecules feel the attractive force of the protocrystal and join in. That's how the crystal begins to grow. 2- What are the factors that affect the growth of the crystal? If the solute is too soluble, this will result in small crystal size. The particle size of a precipitate is influenced by experimental variables as precipitate solubility, temperature, reactant concentrations, and the rate at which reactants are mixed. Crystals grow best if they are undisturbed. 3- Why do the crystals seem to stop growing? It continues growing until eventually, it can no longer remain dissolved in the solution and it falls out of solution. 4- How fast do the crystals grow? in a half a minute? A minute? More? The speed depends upon the supply of the elements, the degree of oversaturation present, and the mechanism of element transport. 5- How large to they get? Now other solute molecules begin growing on the surface of the crystal and it keeps on getting bigger until there is an equilibrium reached between the solute molecules in the crystal and those still dissolved in the solvent.

9 Teacher s Answer Key for Assessments `1. Please discuss below questions at the end of an experiment. A. What problems did you have during the project? How did you solve them? Answers will vary B. How did the solubility of your chemical change as the water was heated and then cooled? As the solvent was heated, its solubility increased as more solute was dissolved by the solvent. When the solvent was cooled, its solubility decreased and solute starts to fall out of the solution. C. Under which conditions could your crystal become smaller while in the beaker of solution? Explain why each would happen and how you could "fix" each problem. My crystal can become smaller if I put it into a solution that is too hot and the solvent dissolves the solute (crystal) because the solution is unsaturated. It can also dissolve if there is too much solvent and the solution is unsaturated. In both cases, adding additional solute until the solution becomes saturated will keep more of the crystal from dissolving. D. Do all chemicals have crystals of the same shape? Suggest reasons to explain why. Not all crystals have the same shape the Copper sulfate crystals look like parallelograms with slanted sides. The Molecules must fit differently in each solute crystal. It must depend on the atoms of the different elements that make up each solute compound and the bonding involved. E. How would you improve what you have done in this project to produce a better crystal? Answers will vary.