Laboratory Procedures
Process Objectives
· To observe proper safety technique with all laboratory equipment.
· To use laboratory apparatus skillfully and efficiently.
LearningObjective
· To learn the names and functions of all the apparatus in the laboratory.
· To develop a positive approach toward laboratory safety.
Introduction
The best way to become familiar with chemical apparatus is to actually handle the pieces yourself in the laboratory. This experiment is divided into several parts in which you will learn how to adjust the gas burner, insert glass tubing into a rubber stopper, use a balance, handle solids, measure liquids, filter a mixture, and measure temperature and heat. Great emphasis is placed on safety precautions that should be observed whenever you perform an experiment and use this apparatus. Several useful manipulative techniques are also illustrated on pages 9 through 1 1 under the heading Techniques and Safety Sketches. In many of the later experiments, references will be made to these Techniques and Safety Sketches. You will also be referred to many of the safety precautions and procedures explained in all parts of this experiment. It is important that all students develop a positive approach to a safe and healthful environment in the laboratory.
Safety
Take the necessary safety precautions before beginning each part of this
experiment. Wear safety goggles, apron, and gloves. Get into the " good habit" of always putting on this standard safety equipment as soon as you enter the lab. It is
important that you and your partner observe all safety precautions while conducting experiments. See pages 3 through 8. Read all safety cautions noted in your procedures and discuss them with your teacher.
Part 1 The Burner
Apparatus
Heat-resistant mat
Forceps
Sparker
Materials
Copper wire, 18 gauge
Recording Your Observations
Record your observations in the spaces provided in each part of this experiment.
Procedures
1. The Bunsen or Tirrell burner is commonly used as a source of heat in the laboratory. Although the details of construction vary among burners, each has a gas inlet located in the base, a vertical tube or barrel in which the gas is mixed with air, and adjustable openings or ports in the base of the barrel. These ports admit air to the gas stream. The burner may have an adjustable needle valve to regulate the flow of gas. In some models the gas flow is regulated simply by adjusting the gas valve on the supply line. The burner is always turned off at the gas valve, never at the needle valve. Look at Figure 1-1 as you examineyour Bunsen burner and locate these parts.
CAUTION Before you light the burner, check to see that you and your partner have taken the following safety precautions against fires: Wear safety goggles, aprons, and gloves. Confine long hair and loose clothing: Tie long hair at the back of the head and away from the front of the face, roll up long sleeves on shirts, blouses, and sweaters away from the wrists. You should also know the locations of fire extinguishers,f ireblankets,safety showers, and sand buckets and how to use them in case of a fire.
Figure 1-1
2. In lighting the burner, partially close the ports at the base of the barrel, turn the gas full on, hold the sparker about 5 cm above the top of the burner, and proceed to light. The gas flow may then be regulated by adjusting the gas valve until the flame has the desired height. If a very low flame is needed, remember that the ports should be partially closed when the gas pressure is reduced. Otherwise the flame may burn inside the base of the barrel. When improperly burning in this way, the barrel will get very hot, and the flame will produce a poisonous gas, carbon monoxide.
CAUTION Carbon monoxide is a poisonous gas.
If the flame is burning inside the base
of the barrel, immediately turn off
the gas at the gas valve. Do not touch
the barrel, for it is extremely hot! Al-
low the barrel of the burner to cool off and then proceed as follows:
Begin again, but first decrease the amount of air admitted to the burner by partly closing the ports. Turn the gas full on and then relight the burner. Control the height of the flame by adjusting the gas valve. By taking these steps, you should acquire a flame that is burning safely and is easily regulated throughout the experiment.
3. Using the forceps, hold an evaporating dish in the tip of the flame for about three minutes. Place the dish on a heat-resistant mat, allow the dish to cool, and then examine its underside. Describe the results and suggest a possible explanation.
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Such a flame is seldom used in the laboratory. For laboratory work, you should adjust the burner so that the flame will be free of yellow color, nonluminous, and also free from the "roaring" sound caused by admitting too much air.
4. A steady flame with a sharply defined, light blue inner cone is recommended. This adjustment gives the highest temperature possible with your burner. Using the forceps, insert a 10-cm piece of copper wire into the flame just above the barrel. Lift the wire slowly up through the flame. Where is the hottest portion of the flame located?
_______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ ____
Hold the wire in this part of the flame for a few seconds. What is the result?
_______________________________________________________________________ _______________________________________________________________________ __
5. Shut off the gas burner. Now think about what you have just observed in Procedures 3 and 4. Why is the nonluminous flame preferred over the yellow luminous flame in the laboratory? (Hint: The melting point of copper is 1083'C.)
_______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ ___
6. At the end of this part of the experiment, all the equipment you store in the tab locker or drawer should be completely cool, clean, and dry. It should also be arranged in an orderly fashion for the next lab experiment. Check to see that the valve on the gas jet is completely shut off. Remember that hands should be washed thoroughly with soap at the conclusion of each laboratory period.
Part 2 Glass Manipulations
1. Inserting glass tubing. Inserting glass tubing into rubber stoppers can be very dangerous. The following precautions should be observed to prevent injuries:
a. Never attempt to insert glass tubing having a jagged end. All glass tubing should be fire polished or have the edges beveled with emery paper before inserting it into a rubber stopper.
b. Use water, soap solution, glycerin, or Vaseline as a lubricant on the ends of the glass tubing before inserting it into a rubber stopper. Ask your teacher for the proper lubricant.
CAUTION Make certain you are wearing gloves, preferably leather ones, when
handling the glass tubing. If leather gloves are not available, wear rubber gloves and wrap a layer of cloth around the glass tubing before inserting it into the stopper. See Figure 1-2.
c. Hold the glass tubing as close as possible to the part where it is entering the rubber stopper. Remember, always aim the glass tubing away from the palm of the hand that holds the stopper. Using a twisting motion, gently insert the tube into the hole of the stopper as far as desired. See Figure 1-2.
d. At the end of the experiment, immediately remove the rubber stoppers from the tubing to keep them from sticking or "freezing" to the glass tube. Use a lubricant as mentioned in (b) if the stopper or tubing won't budge. When removing the stopper, follow the precautions that were
2. Wheninserting glass tubing into a rubber or plastic hose, observe the same precautions discussed in l(a) and l(d). The glass tubing should be lubricated before insertion into the rubber or plastic hose, and the rubber hose should be cut at an angle before the insertion of the glass piece. The angled cut allows the rubber to stretch more readily.
CAUTION Wear gloves and wrap a layer of cloth around the glass tubing before inserting it into the rubber or plastic hose.
At the end of an experiment, immediately remove the glass tubing from the hose
In many experiments you are required to insert glass tubing into both a rubber stopper and a rubber hose. Carefully follow these precautions and techniques when inserting glass tubing. You will be referred to these safety precautions throughout the entire lab course.
Part 3 Handling Solids
Apparatus
test tube Spatula
glazed paper
Materials
Sodium chloride
Procedures
1. Solids are usually kept in wide-mouthed bottles. A spatula should be used to dip out the solid. See Figure 1-3.
CAUTION Do not touch chemicals with your
hands. Some chemical reagents readily pass through the skin barrier into the bloodstream and can cause serious health problems. Some chemicals are extremely corrosive. Always wear
gloves, apron, and safety goggles when handling chemicals. Carefully check the label on the reagent bottle or container before removing any of the
contents. Never use more of a chemical than directed. You should also know the locations of the lab shower and eyewash and how to use them in case of an accident.
2. Remove a spoonful of sodium chloride from its reagent bottle. In order to transfer the sodium chloride to a test tube, first place it on a piece of glazed paper about 10 cm square. Roll the paper into a cylinder and slide it into a test tube that is lying flat on the table. When you lift the tube to a vertical position and tap the paper gently, the solid will slide down into the test
tube. See Figure 1-4.
Cautions never try to pour a solid from a bottle into a test tube. As a precaution against contamination, never pour unused chemicals back into their reagent bottles.
3. Throw the solid sodium chloride and glazed paper into the waste jars or containers provided by your teacher.
Cautions Never discard chemicals or broken glassware in the wastepaper basket. This is an important safety precaution against fires, and it prevents personal injuries (such as hand cuts) to anyone who empties the wastepaper basket.
4. Remember to clean up the lab and wash your hands thoroughly at the end of this part of the experiment.
Part 4 The Balance
Apparatus
Centigram balance Spatula
Weighing paper
Materials
Sodium chloride
Procedures
1. When a balance is required for determining mass, you will use a centigram balance. See Figure 1-5. The centigram balance is sensitive to 0.01 g. This means that your mass readings should all be recorded to the nearest 0.01 g.
2. Before using the balance, always check to see if the pointer is resting at zero. If the pointer is not at zero, check the slider weights. If all the slider weights are at zero, turn the zero adjust knob until the pointer rests at zero. The zero adjust knob is usually located at the far left end of the balance beam. See Figure 1-5. Note: The balance will not adjust to zero if the movable pan has been removed. Whenever weighing chemicals, always
Figure 1-5
use weighing paper or a glass container. Never place chemicals or hot objects directly on the balance pan. They can permanently damage the surface of the balance pan and affect the mass weighing.
3. In many experiments you will be asked to weigh out a specified amount of a chemical solid.
CAUTION Do not touch chemicals with your hands. Always wear gloves, apron, and safety goggles when handling chemicals. Carefully check the label on the reagent bottle or container before removing any of the contents. Never use more of a chemical than directed; you should know the locations of the safety shower and eyewash and how to use them in case of an accident.
Use the following procedures to obtain 13 grams of sodium chloride.
a. Make sure the pointer on the balance is set at zero. Obtain a piece of weighing paper and place it on the balance pan. Determine the mass of the paper by adjusting@@6e weights on the various scales. Record the mass of the weighing paper to the nearest 0.01 g.
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b. Add 13 grams to the balance by sliding over the weight of the 10-gram scale to 10 and the weight of the 1-gram scale to 3.
c. Using a spoon obtain a quantity of sodium chloride from a reagent bottle and place it on a separate piece of paper.
d. Now slowly pour the sodium chloride from the glazed paper onto the weighing paper in the balance pan, until the pointer once again comes to zero. In most cases, you will only have to be close to the specified value. Do not waste time by trying to obtain exactly 13.00 g. Instead, read the mass when the pointer swings close to zero. For example, suppose you slightly overshot the zero point. Adjust the appropriate weights and read the value. The mass might be 13.18 g. This value would be just as satisfactory as 13.00 g. Record your mass of sodium chloride to the nearest 0.01 9.
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4. Throw the sodium chloride and weighing paper in the waste jars or containers provided by your teacher.
Cautions Never discard chemicals, weighing papers, broken glassware, matches or the like in the wastepaper basket. This is an important safety precaution against fires, and it prevents personal injuries (such as hand cuts) to anyone who empties the wastepaper basket. As a precaution against contamination, never pour unused chemicals back into their reagent bottles.
5. Hands should be washed thoroughly with soap and water at the conclusion
Part 5 Measuring Liquids
Apparatus
Graduated cylinder pipette
Buret clamp ring stand
Buret beakers, 100 mL, 250 mL
Materials
Water
Procedures
1. For approximate measurements of liquids, a graduated cylinder such as the one shown in Figure 1-6 is generally used. These cylinders are usually
graduated in milliliters (mL). Such a graduated cylinder may read from 0 to 10 mL, 0 to 25 mL, or more, from bottom to top. It may also have a second row of graduations reading from top to bottom. Examine your cylinder for these markings.
Observation:________________________________________________ __________________________________________________________ ________________________________________________________
2. A pipette or a buret is used for more accurate measurements. Pipettes are made in many sizes and are used to deliver measured volumes of liquids. A pipette is fitted with a suction bulb, which is used to withdraw air from the pipette while drawing up the liquid to be measured. See Figure 1-7. Always use the suction bulb-NEVER pipette by mouth.
3. Burets, fitted with a stopcock, a pinch clamp, or a glass
bead, are used for delivering any desired quantity of liquid up to the capacity of the buret. Many burets are graduated in tenths of milliliters. See Figures 1-8 and 1-9. When using a buret, follow these steps:
a. Clamp the buret in position on a ring stand. See Figure 1-10.
b. Place a beaker, 250-mL, at the bottom of the buret. The beaker serves to catch any liquid that will be drawn off.
c. Pour into a 50-mL beaker a quantity of the liquid you want to measure from the liquid's reagent bottle. (NOTE: In this first trial you will be using water.) Remember to carefully check the label of the reagent bottle before removing any liquid.
CAUTION Safety goggles; gloves, and apron should be worn whenever you measure chemicals. Never pour a liquid directly from its reagent bottle into the buret. You should first pour the liquid into a small beaker (50-mL) that is easy to handle. Then pour the liquid from the small beaker into the buret. This simple method will prevent unnecessary spillage. Never pour any unused liquid back into the reagent bottle.
d. Fill the buret with the liquid and then draw off enough liquid to fill the tip below the stopcock and bring the level of the liquid down to scale. The height at which the liquid stands is then read accurately. Practice this procedure several times by pouring water into the buret and emptying it through the stopcock.
4.
Observe that the surface of a liquid in the buret is slightly curved. It is concave if it wets the glass, and convex if it does not wet the glass. Such a curved surface is called a
meniscus. If the liquid wets the glass, you read
to the bottom of the meniscus, as shown in Figure 1-11. You must read the mark at the bottom of the meniscus. This is the line AB. If you read the markings at the top of
the meniscus, CD, you will get an incorrect reading. Locate the bottom of the meniscus when reading the water level in the buret.
Observation: __________________________________________________ __________________________________________________ __________________________________________________ ________________________________
5. After you have taken your first buret reading, as directed, open the stopcock and draw off as many milliliters of the liquid as you wish. The exact amount drawn off is equal to the difference between your first and final buret readings. Practice measuring liquids by measuring 10 mL of water, first using a graduated cylinder, then a pipette, and finally a buret.
6. At the end of this part of the experiment, the equipment you
store in the lab locker or drawer should be clean, dry, and arranged in an orderly fashion for the next lab experiment.
CAUTIONin my, experiments you will have to dispose of a liquid chemical at the end of a lab. Always ask your teacher for the correct method of disposal. in many instances liquid chemicals can be washed down' the sink's drain by diluting them with plenty of tap water. Very toxic chemicals should be handled only by a teacher. All apparatus should be washed, rinsed, and dried.
7. Remember to wash your hands thoroughly at the end of this part of the experiment.
Part 6 Filtration
Apparatus
ring stand filter paper
stirring rod iron ring
ceramic-centered wire gauze burner and tubing
evaporating dish two beakers, 250 mL
sparker funnel
wash bottle
Materials
sodium chloride fine sand
water
Procedures
1. Sometimes liquids contain particles of insoluble solids, present either as impurities or as precipitates formed by the interaction of the chemicals used in the experiment. If the particles are denser than water, they soon sink to the bottom. Most of the clear, supernatant (floating above) liquid may be poured off without disturbing the precipitate. Such a method of separation is known as decantation. See page 9 for the proper techniques.
Observation: _______________________________________________________________________ _________________________________________________________________
2. Fine particles, or particles that settle slowly are often separated from a liquid by filtration. Support a funnel on a small ring on the ring stand as shown in Figure 1-12. Use a beaker to collect the filtrate. Adjust the funnel so that the stem of the funnel just touches the inside wall of the beaker.
Observation: ____________________________________________________________ ______
3. Fold a circular piece of filter paper along its diameter, and then fold it again to form a quadrant. See Figure 1-13. Separate the folds of the filter, with three thicknesses on one side and one on the other; then place in the funnel. The funnel should be wet before the -paper is added. Use your plastic wash bottle. Then wet the filter paper with a little water and press the edges firmly against the sides of the funnel so no air can get between the funnel and the filter paper while the liquid is being filtered. EXCEPTION. A filter should not be wet with water when the liquid to be filtered does not mix with water Why?
4. Dissolve 2 or 3 g of salt in a beaker containing about 50 mL of water, and stir into the solution an equal bulk of fine sand. Then filter out the sand by pouring the mixture into the filter, observing the following suggestions:
a. The filter paper should not extend above the edge of the funnel. It is better to use a filter disc that leaves about 1 cm of the funnel exposed.
b. Do not fill the filter. It must never overflow.
c. Try to establish a water column in the stem of the funnel, thus excluding air bubbles, and then add the liquid just fast enough to keep the level about I cm from the top of the filter
d. When a liquid is poured from a beaker or other container, it may adhere to the glass and run down the outside wall. This may be avoided by holding a stirring rod against the lip of the beaker, as shown in Figure 1-12. The liquid will run down the rod and drop off into the funnel without running down the side of the beaker. The sand is retained on the filter paper. What property of the sand enables it to be separated from the water by filtration?
5.The salt can be recovered from the filtrate by pouring the filtrate into an evaporating dish and evaporating it nearly to dryness. See Figure 1-14 for the correct setup.
CAUTION When using the burner, make certainthat you confine loose clothing and that long hair is securely tied back.Wear your safety goggles, apron and
6. Remove the flame as soon as the liquid begins to spatter. Shut off the gas. What property of salt prevents it from being separated from the water by filtration?
7. At the end of this part of the experiment, all equipment you store in the lab locker or drawer should be completely cool, clean, dry, and arranged in an orderly fashion for the next lab experiment. Check to see that the valve on the gas jet is completely turned off. Make certain that the filter papers and sand are thrown into waste jars or containers and not down the sink! Wash your hands thoroughly before leaving the lab.
Part 7 Measuring Temperature and Heat
Apparatus
calorimeter (plastic cups and lid) buret clamp
ceramic-centered wire gauze graduated cylinder
burner and tubing beaker, 250 mL
Celsius thermometer sparker
Beaker tongs ring stand
iron ring
Materials
water
Procedures
A thermometer is used to measure temperature and temperature changes. Examine your thermometer and the temperature range for the Celsius temperature scale. Compare the Celsius scale with the Fahrenheit scale as shown in Figure 1-15.
Observation:________________________________________ __________________________________________________ __________________________________________________ ____
CAUTION If your mercury thermometer should ever break, immediately notify your teacher. Your teacher will clean up the pill. Do not touch the mercury. Refer to the procedures for cleaning up mercury spills on page 7.
2. Examine the calorimeter pictured in Figure 1-16. A calorimeter is an apparatus used in measurements involving heat and heat transfer. For approximate measurements, the simple calorimeter that is shown may be used. The small quantities of heat that may be transferred to or from the calorimeter may be disregarded because of the insulating characteristics of the plastic material of which it is composed.
3. Adjust the position of the thermometer in the calorimeter lid so that the bottom of the thermometer is approximately 1.0 cm above the bottom of the inside cup.
4. Measure 50 mL of tap water in a graduated cylinder, and pour
it into your calorimeter. Record the temperature of the water in this Data table.
5. Pour 50 mL of water into a 250-mL beaker. Warm the water to about 60'C, using the apparatus setup as in Figure 1-17.
CAUTION When using the burner, make certain that you confine loose clothing and that long hair is securely tied back. You should know the locations of fire extinguishers and how to operate them. The beaker becomes hot after heating. Use beaker tongs when handling the beaker of hot water. Gloves should be worn!
6. Turn off the gas burner as soon as the temperature reaches about 60'C. Record the temperature of the hot water. Then, using beaker tongs to hold the beaker, immediately transfer the hot water to the calorimeter cup. Replace the lid, insert the thermometer, and stir the contents gently until a fixed temperature is reached. Record this final temperature in the Data table.
7. At the end of this experiment, all the equipment you store in the tab locker or drawer should be completely cool, clean, dry and arranged in an orderly fashion for the next lab experiment. Check to see that the valve on the gas jet is completely turned off. Remember to wash your hands before leaving the lab.
Data Table
Volume of cold water ______mL
Temperature of cold water ______oC
Volume of hot water ______mL
Temperature of hot water ______oC
Final temperature of mixture ______oC
Calculations
Show your computations. Place your answers in the Calculations table.
1. Calculate the temperature change of the cold water. Final temperature - initial temperature = temperature change of cold water
2. Calculate the temperature change of the hot water. Initial temperature - final temperature = temperature change of hot water
3. The quantity of heat, Q, that is gained and lost may be calculated from the following equation:
Q(in joules) = temperature change (CO) x mass (g) x 4.18 J/g x CO
a. Using this equation, calculate Q for the heat gained by the 50 mL of cold water. Assume that 50 mL of water has a mass of 50 g.
b. Using this equation, calculate Q for the heat lost by the hot water.
c. How do these two quantities compare?
Calculations Table
Temperature change of cold water ______CO
Temperature change of hot water ______CO
Heat gained by cold water ______J
Heat lost by hot water ______J
Questions
Answer the following questions in complete sentences.
1.As soon as you enter the lab, what safety equipment should you put on immediately?
2. Before doing an experiment, what should you read and discuss with your teacher?
3. Before you light a burner, what safety precautions should always be followed?
4. What immediate action should you take when the flame of your burner is burning inside the base of the barrel?
5. What type of flame is preferred for laboratory work and why?
6. Why is it important that you wear safety goggles and gloves and cover the tubing and stopper with a protective cloth layer when inserting glass tubing?
7. What is a common cause of fires in lab drawers or lockers?
8. Why are broken glassware, chemicals, matches, etc. never thrown into a wastepaper basket?
9.List the safety precautions that should be observed when inserting glass tubing into a stopper or rubber hose.
10. Why should you never touch chemicals with your hands?
11. What precaution can you take against chemical contamination in reagent bottles?
12. Why are chemicals and hot objects never placed directly on a balance pan?
13. List three instruments used in the laboratory for measuring small quantities of liquids. What precautions should be taken when fillinga buret with liquid?
14. What is the rule about the size of filter paper to be used with a funnel?
15. How can a liquid be transferred from a beaker to a funnel without spattering and without running down the outside wall of the beaker?
16. How should a thermometer be positioned in the calorimeter lid?
17. In what condition should all lab equipment be stored at the end of an experiment? What else should be checked?
Safety Check
Identify the following safety symbols:
Labeling
Practice labeling a chemical container orbottle filling in the appropriate information missing on the label pictured below. Use 6 M sodium hydroxide (NAOH) as the solution to be labeled. Hint: 6 M sodium hydroxide is a caustic and corrosive solution and can be considered as potentially hazardous as 6 M HCI. See page 8.
SAMPLE LABEL
True or False
Read the following statements and indicate whether they are true or false. Place your answer in the space next to the statement.
___1.Never work alone in the Laboratory.
___2.Never lay the stopper of reagent bottle on the lab table.
___3.At the end of an experiment, in order to save the school's money, save all excess chemicals
___4.The quickest and safest way to heat a material in a test tube is by concentrating the flame on the bottom of the test tube.
___5.Use care in selecting glassware for high temperature heating. Glassware should be Pyrex or a similar heat-treated type.
___6.A mortar and pestle should be used for grinding only one substance at a time.
___7.Safety goggles protect your eyes from particle and chemical injuries. It is completely safe to wear contact lenses under them while performing experiments.
___8.Never use the wastepaper basket for disposal of chemicals.
___9. First Aid Kits may be used by anyone to give emergency treatment after an accident.
___10. Eye and face wash fountains and safety showers should be checked daily for proper operation.
Chemical Apparatus
Identify each piece of apparatus. Place your answers in the spaces provided.
