Experiment-1-Common-Laboratory-Operations.pdf

Cebu Doctors’ University College of Arts and Sciences Physical Sciences Department Name: _________________________________...

Cebu Doctors’ University College of Arts and Sciences Physical Sciences Department Name: _________________________________ Date: ____________ Program, Year and Section: ________________ Experiment 1 – Common Laboratory Operations Intended Learning Outcomes: At the end of this experiment, you will be able to: 1. Demonstrate the proper techniques for the commonly encountered techniques in the laboratory, such as: i. Operation of the Bunsen burner ii. Transferring of Solid and Liquid Chemicals iii. Heating Liquids iv. Filtration v. Evaporation vi. Testing for Solubility Apparatus and Equipment: Bunsen burner, test tubes, beakers, Erlenmeyer flask, stirring rod, funnel, water bath, test tube holder, tripod, wire gauze, filter paper, evaporating dish, top loading balance Materials: potassium iodide (KI) solution, lead (II) nitrate [Pb(NO3)2] solution Welcome to the chemistry laboratory! For the next few months in your life, you will be spending some of your memorable times here. To make your stay in the chemistry lab a memorable one, you need to avoid accidents. Avoiding accidents mean strictly following all necessary rules of operations. For this experiment, you will be introduced to basic experimental techniques and associated glassware and apparatus that are commonly used in the biochemistry laboratory. You need to remember that in the future, when conducting experiments, you need to strictly follow the rules written here. I. OPERATION OF THE BUNSEN BURNER Fig. 1: Bunsen Burner Source: https://www.pngitem.com/middle/iimRRbR_bunsen-burner-clip-art-hd-png-download/ 1|Page Whenever flame or heating is required in the chemistry lab, we commonly use the Bunsen burner. Thus, it is imperative that you identify its parts, know its functions, and operate the burner itself. Shown on the previous page is a diagram of a Bunsen burner. Label the parts accordingly before the start of the lab period. Safety Precautions to Follow During the Operation of the Bunsen Burner PLACE the Bunsen burner away from any overhead shelving, equipment, or light fixtures. REMOVE all papers, combustible materials, and chemicals from the area. TIE-BACK any long hair, dangling jewelry, or loose clothing. INSPECT hose for cracks, holes, pinched points, or any other defect and ensure that the hose fits securely on the gas valve and the Bunsen burner. NOTIFY others in the laboratory the burner will be in use. ADJUST the flame by turning the collar to regulate air flow and produce an appropriate flame for the experiment. DO NOT leave open flames unattended. SHUT OFF gas when its use is complete. ALLOW the burner to cool before handling. ENSURE that the main gas valve is off before leaving the laboratory. Types of Bunsen Burner Flame Generally, the Bunsen burner has two types of flame: 1. Luminous flame - also known as safety flame. It can be obtained when the air hole is fully closed. This is the coolest flame characterized by bright yellow color producing black soot on top of the flame. The production of soot indicates that combustion of the fuel in this type of flame is incomplete. A luminous flame is never used in heating. It is just used when starting a burner. 2. Non-luminous flame - This is the flame used for heating. It can be obtained when the air hole is fully opened. This is characterized by a faint blue color that is difficult to see in a well-lit room. There is no soot production when using this flame indicating that the combustion of fuel is complete. Lighting the Bunsen Burner 1. Close the air hole of the burner by adjusting the collar. This ensures that you start with a yellow flame (luminous flame/safety flame). 2. Connect the burner hose to the gas outlet. The gas outlet handle should be in the fully closed position. 3. Ignite a matchstick. Place the lit matchstick at the side of the tip of the barrel. 4. Gradually, open the gas outlet handle until flame catches on top of the barrel. 5. Open the air hole by adjusting the collar to produce blue flame (non-luminous flame). This is the flame to be used for experiments. 6. Adjust the length of the flame by adjusting the opening of the gas outlet. 7. When turning off, start by closing the air hole. Then, close the gas outlet. 8. Disconnect the burner hose from the gas outlet. Guide questions: 1. Describe the flame of a properly burning Bunsen burner? ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ 2. What does it mean if you have bright yellow flame? How do you correct the problem? ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ 2|Page 3. Why is a luminous flame not used during heating? ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ II. WEIGHING AND TRANSFERRING SOLID CHEMICALS Solid chemicals are generally kept in reagent bottles. Removal of solid chemicals from the reagent bottle should be done by spatula or paper, not by bare hands. Any excess chemical that is already taken out from the bottle should not be returned but should be disposed in designated waste disposal bin. Weighing Solid Chemicals Using to Loading Balance There are experiments that would require using measured amount of chemicals to be used, such as its weight. Weighing is a very crucial process in the chemistry laboratory to obtain accurate results. There are a lot of balances that could be used for this purpose, specifically double beam balance, top-loading balance, and analytical balance. Before any weighing could take place, it must be noted that the balance should be clean and all apparatuses that will be used for weighing should be clean and dry. For this experiment, you will be doing weighing using the to-loading balance as this type will be useful in your case. Procedure: 1. Turn on the top-loading balance and wait until you see a 0.0 g in the screen. 2. Place a small beaker on the pan of the balance. This will serve as your weighing container. Wait until the digits in the screen stop moving. 3. Press “Tare”. Taring automatically zeroes the mass of the container. 4. Open the lid of the reagent bottle containing salt and lay the flat side of the lid on the table. 5. From the reagent bottle provided, transfer salt into the beaker using a spatula, small amount at a time until the screen of the balance read 1.0 g. Do not return any excess sand back into the reagent bottle. 6. Remove the beaker and set aside. Transferring Solid Chemicals in a Test Tube Most chemical tests are done in a test tube. Although it seems very easy and simple, but transferring solid chemical into a test tube can cause a lot of errors if not executed properly. Before transferring any solid chemicals into the test tube, it must be first noted that all the apparatuses to be used should be clean and dry to avoid contamination. The following procedure will teach you how to transfer solid chemical from a reagent bottle to a test tube. Procedure: 1. Cut a piece of paper with a width like the opening of a test tube and height that is like that of the test tube with at least 2 cm excess. Fold the paper lengthwise. 2. Using a provided spatula, scoop the previously weighed salt in the beaker and transfer it on the trough of the folded paper. 3. Fold the paper to secure the sand and carefully insert it inside the test tube until the tip touches the bottom of the tube. 4. Gently tap the body of the test tube to deliver the solid directly to the bottom. 5. Close the reagent bottle. Keep the test tube with the sand for the following experiments. Guide Question: 1. Why should any excess chemical not be returned to the reagent bottle? ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ 3|Page 2. Why is the use of funnel no longer advisable when transferring solid into a test tube? ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ III. MEASURING THE VOLUME AND TRANSFERRING LIQUID CHEMICALS Some of the chemicals you will encounter in the chemistry lab are in the form of solutions. It must be put to mind that most solutions, even the hazardous ones, look like just water. Therefore, you need to handle all solutions with care. Measuring the Volume of Liquid Chemicals Using Graduated Cylinder Like solid chemicals, measured of amounts of liquids may also be required in experiments, usually by its volume. There are a lot of apparatus for measuring volumes of liquid, but commonly we used the graduated cylinder. Take note that a beaker and an Erlenmeyer flask should not be used in measuring volumes although they have graduation marks on them. They are mainly used for containment of liquid chemicals. Procedure: 1. Half-fill a beaker with tap water from the faucet. 2. Measure 10 mL of water from the beaker using the graduated cylinder following the procedure below: a. Touch mouth of the beaker to the mouth of the graduated cylinder and slowly pour water until it reaches the line just a little below the 10 mL mark. b. With a dropper, add water into the graduated cylinder until the lower meniscus of the water inside the cylinder touches the 10 mL mark. Transferring Liquid Chemicals There are plenty of glassware in the laboratory for the containment of liquid chemicals, such as beaker, test tubes, and Erlenmeyer flasks. Some of them have indentation while others have none. An indentation is the cleft in the mouth of glassware like the one in beakers. For this experiment, you will be doing transferring of liquid from glassware with and without indentation and using a dropper. indentation Fig. 2: Beaker Source: https://cdn.images.fecom-media.com/HE1788994_1424793-PHE-PHY-P01.jpg?width=348&quality=75%201x,%20https://cdn.images.fecom- media.com/HE1788994_1424793-PHE-PHY-P01.jpg?width=696&quality=75%202x Procedure: Transferring Liquid from Glassware with Indentation 1. Transfer the measured water in the graduated cylinder into the test tube from the previous procedure containing sand by touching indentation of the graduated to the mouth of the test tube and slowly pour the water until all its content is poured. Transferring Liquid from Glassware without Indentation 1. Half-fill an Erlenmeyer flask with tap water. 2. Place a glass stirring rod inside another test tube that is securely standing in a test tube rack. 4|Page  3. Deliver water from the Erlenmeyer flask into the test tube by carefully running the water down through the stirring rod until the test tube is filled not more than 1/3 of its total volume. Label the test tube “for heating” and set aside. Transferring Liquid Using Dropper 1. From the provided chemicals in the bench, transfer 20 drops of potassium iodide solution in a test tube using the provided dropper. Label with “KI”, cover with cork, and set aside. (Note: As a rough estimate when using dropper, 20 drops is equivalent to 1 mL.) 2. Into another test tube, transfer 20 drops of lead(II) nitrate solution using the provided dropper. Label with “Pb(NO3)2”, cover with cork, and set aside. (Note: Each reagent has its own dropper. Do not interchange to avoid contamination.) Fig. 3: Transferring Liquid Using Dropper Source: https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Book%3A_Organic_Chemistry_Lab_Techniques_(Nichols)/01%3A_General_Techniques/1.02%3A_Transferring_ Methods/1.2.0B%3A_1.2B%3A_Transferring_Methods_-_Liquids IV. HEATING LIQUIDS Most reactions in the chemistry laboratory occur above room temperature. In this case, heating is necessary. The flame during heating, as discussed previously, should be a non-luminous flame of a Bunsen burner. Illustrated below are 2 set-ups for heating liquids: Fig. 4: Two Ways of Heating Liquids Sources: Set up A: http://summerchemistryomeara.weebly.com/uploads/3/8/0/0/38007353/bunsenburner.pdf Set up B: http://intro.chem.okstate.edu/ChemSource/Inorganic/Inorganic_28.html Set up A is used to heat non-volatile and non-flammable liquids, such as water. On the other hand, set up B is heating in a water bath and is used for heating volatile and flammable liquids, such as alcohol. The set-up is applicable when heating 1-3 test tubes. If you are required to heat 4 or more test tubes, use the water pan that is provided to you for more space. Procedure: 1. Obtain the test tube from transferring liquid procedure that is labeled “for heating”. Note that this test tube contains water that occupies not more than 1/3 of the test tube’s total volume. This volume 5|Page  should be followed every time you are heating. Heat the liquid in the test tube using Set up A. Follow the procedures below: a. Operate the Bunsen burner to give a non-luminous flame. b. Securely fasten the labeled test tube with water with a test tube holder. c. Do not cover the test tube with anything. d. Heat the test tube at the surface of the water while slanting it at 45o angle. Make sure that the mouth is pointing away from you or from anybody. 2. Fill another test tube with water not more than 1/3 of its total volume. Pretending the water inside is a flammable solution, such as ethanol, heat the test tube using Set Up B. Follow the procedures below: a. Half-fill a 500 mL beaker with water. b. Construct a set up similar to Set up B making sure to use non-luminous flame. c. Heat the water in the beaker until boiling. d. Secure the test tube with a test tube holder and place in the water inside the beaker. Guide Questions: 1. Why is not good to cover the test tube with a cork while heating? ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ 2. Why are flammable liquid not heated using Set up A (direct heating)? ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ 3. When heating liquid using Set up A, what is the importance of moving the test tube back and forth through the flame? ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ V. FILTRATION Filtration is a process of separating solid from liquid solution using a filtration membrane, in most cases a filter paper. It has two main purposes. The first is to remove solid impurities from a liquid. The second is to collect a desired solid from the solution from which it was precipitated. The following illustration shows a filtration set up, known as gravity filtration: Fig. 5: Filtration Source: https://www.bitlanders.com/blogs/filtration/195691 6|Page The solid that is left on the filter paper after filtration is called residue. The liquid that comes out from the filter paper is called filtrate. The filter paper should be folded properly to ensure efficient filtration. The following illustration shows the proper way of folding filter paper: Fig. 6: Folding and Mounting of Filter Paper Source: https://community.asdlib.org/imageandvideoexchangeforum/2013/07/24/gravity-filtration/ Procedure: 1. In a clean and dry test tube, mix the contents of the test tubes labeled “KI” and “Pb(NO3)2” from the previous procedure of transferring liquids. Note that a colored solid is formed upon mixing. The solid that is formed is called a precipitate. What is the color of the precipitate? _____________________ 2. Construct a gravity filtration set up similar as the illustration presented before using properly folded filter paper. 3. Pour the mixture containing the colored precipitate into the filter paper on the filtration set up. Notice that the colored precipitate remains on the filter paper and a colorless solution comes out from the filter paper. 4. Wash out the remaining precipitate from the test tube with small amount of water and pour into the filter paper. 5. Set aside the filtrate and label the flask with “for evaporation.” Guide Questions: 1. What type of reaction has occurred when you mixed the 2 solutions together? What evidence of chemical reaction is observed? ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ 2. What is the chemical name and formula of the residue on the filter paper? ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ 3. What is the chemical name and formula of the soluble component of the reaction that is present in the filtrate? ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ 7|Page VI. EVAPORATION Evaporation is a process of separating soluble solids from a solution. This is carried out by evaporating the solvent to dryness leaving the solute residue behind. The following illustration shows the set-up for evaporation: Fig. 7: Evaporation Source: https://abbathetwiter.blogspot.com/2019/12/diagram-bunsen-burner-evaporation.html As the solvent from the solution dries up, a solid product remains. This is called residue. Procedure: 1. Set up the equipment shown in the previous illustration. 2. Obtain the flask labeled “for evaporation” and pour the content into the evaporating dish of the set up. 3. Heat the mixture in the evaporating dish until the solution dries up. Notice that a solid remains in the evaporating dish. Describe the appearance of the residue left in the evaporating dish. ________________________________________________ Guide Questions: 1. Why can’t evaporation be carried out in an Erlenmeyer flask? ________________________________________________________________________________________ ________________________________________________________________________________________ ________________________________________________________________________________________ VIII. TESTING FOR SOLUBILITY The solubility of a solute (a dissolved substance) in a solvent (the dissolving medium) is the most important chemical principle underlying some of the basic techniques in the organic chemistry laboratory, such as recrystallization, extraction, and chromatography. Although we often describe solubility behavior in terms of a substance being soluble (dissolved) or insoluble (not dissolved) in a solvent, solubility can be described more precisely in terms of the extent to which a substance is soluble. Solubility may be expressed in terms of grams of solute per liter (g/L) or milligrams of solute per milliliter (mg/mL) of solvent. Consider the solubilities at room temperature for the following three substances in water: Cholesterol 0.002 mg/mL Caffeine 22 mg/mL Citric acid 620 mg/mL In a typical test for solubility, 40 mg of solute (a pinch) is added to 1 mL of solvent. Therefore, if you were testing the solubility of these three substances, cholesterol would be insoluble, caffeine would be partially soluble, and citric acid would be soluble. 8|Page When the solubility of a liquid solute in a solvent is described, it is sometimes helpful to use the terms miscible and immiscible. Two liquids that are miscible will mix homogeneously (one phase) in all proportions. For example, water and ethyl alcohol are miscible. When they are mixed in any proportion, only one layer will be observed. When two liquids are miscible, it is also true that either one of them will be completely soluble in the other one. Two immiscible liquids do not mix homogeneously in all proportions, and under some conditions they will form two layers. Water and diethyl ether are immiscible. When mixed in roughly equal amounts, they will form two layers. A useful generalization in predicting solubility is the widely used rule “Like dissolves like.” This rule is most applied to polar and nonpolar compounds. According to this rule, a polar solvent will dissolve polar (or ionic) compounds, and a nonpolar solvent will dissolve nonpolar compounds. Below is a list of organic compounds with their corresponding polarities: Procedure: Solubility of Solid Compounds: 1. Place about 40 mg (small pinch) of benzoic acid into each of four dry test tubes. 2. Label the test tubes and then add 1 mL of water to the first tube, 1 mL of ethyl alcohol to the second tube, and 1 mL of hexane to the third tube. The fourth tube will serve as a control. 3. Determine the solubility of each sample in the following way: a. Using the rounded end of a stirring rod, stir each sample continuously for 60 seconds by twirling the spatula rapidly. b. After 60 seconds (do not stir longer), note whether the compound is soluble (dissolves completely), insoluble (none of it dissolves), or partially soluble. You should compare each tube with the control in making these determinations. You should state that a sample is partially soluble only if a significant amount (at least 50%) of the solid has dissolved. If it is not clear that a significant amount of solid has dissolved, then state that the sample is insoluble. If all but a couple of granules have dissolved, state that the sample is soluble. c. Record these results in the table 1 below. 4. Repeat the directions just given, substituting citric acid for benzoic acid. 9|Page  Water Ethyl alcohol Hexane Organic Compounds (highly polar) (intermediate polarity) (nonpolar) Benzoic acid Citric acid Miscibility of Pairs of Liquids: 1. For each of the following pairs of compounds in the table, add 1 mL of each liquid to the same test tube. Use a different test tube for each pair. 2. Shake the test tube for 10–20 seconds to determine whether the two liquids are miscible (form one layer) or immiscible (form two layers). 3. Record your results in the table below. Pairs of Compounds Miscibility Water and ethyl alcohol Water and hexane Water and diethyl ether Ethyl alcohol and hexane Hexane and diethyl ether 10 | P a g e