SAFE PRACTICEINCHEMISTRYLABORATORY
Successful work in the chemistrylaboratory involves not onlymastery of chemical conceptsand techniques, but also knowing:
• the hazards around you,
• what the safety requirements are,
• what equipment is available, and
• when and how to use each piece ofequipment.
•Chemical hazard, such as corrosives, flammables,toxics, explosives,…etc
•Biological hazard, such as pathogenicmicroorganisms, biological tissues, animals.
•Physical hazard, such as noise, radiation.
•Electrical/Mechanical hazard, such as high voltageapparatus, machinery with moving parts.
•Psychological hazard, such as emotional stress.
Laboratory Hazard
Therefore, it is very important before entering any lab to identify the sources of hazard and follow the safety rules to protect yourself and to be sure about your safety.
Laboratory Hazard
ClothingWear:
• Goggles/safetyglasses
• Closed-toed shoes
• Clothing made ofnatural based fibersuch as cotton
• Tie back long hair
Do notWear:
• Sandals
• Jewelry
• Loose or Baggyclothing
Personal Protective Equipments
General lab Safety Rules
1. Work in the lab only when the instructor is present or when you have permission to do so.
2. Listen to or read instructions carefully before attempting to do anything.
3. Identify any source of hazards present in the lab and report to the instructor.
4. Learn the location and proper usage of the eyewash fountain, fire extinguisher, safety shower, fire alarm box, office intercom button, evacuation routes, cleanup brush and dust pan, glass/chemical disposal can.
5. Report all accidents regardless of how minor to your instructor.
6. Before beginning work in lab, clean the lab bench top and your glassware.
7. Never indulge in horseplay or behavior that could lead to injury of others.
8. Use goggles and lab coat all the time inside the lab. 9
9. Read the label on chemical bottles at least twice before using the chemical. Many chemicals have names that are easily confused.
10. Due to the dangers of broken glass and corrosive liquid spills in the lab, open sandals or bare feet are not permitted in the lab.
11. If you get any chemical in your eye, immediately wash the eye with the eyewash fountain and notify the instructor.
12. Never look directly into a test tube. View the contents from the side.
13. For minor skin burns, immediately plunge the burned area into cold water and notify the instructor.
14. Never smell a material in a test tube or flask directly. Instead, with your hand, "fan" some of the fumes to your nose carefully.
15. Immediately notify the instructor of any chemical spill and clean up the spill as directed.
16. Never take chemical stock bottles to the lab benches.
17. Use equipment only as directed:
a. never place chemicals directly on the pan balances.
b. use glycerin when insertingglass tubing into rubber stoppers.
c. be cautious of glassware that has been heated.
d. add boiling chips to liquid that is to be heated
before heating.
e. point test tubes that are being heated away from you and others.
16. Never taste any material in the lab
17. Food, drink and gum are prohibited in lab.
18. Never add water to concentrated acid solutions. The heat generated may cause spattering. Instead, as you stir, add the acid slowly to water.
19. Return all lab materials and equipment to their proper places after use.
20. Upon completion of work, wash and dry all equipment, your lab bench and your clean-up area.
Always wash your hands thoroughly to remove any potential chemical residues before you leave the lab.
Washing Hands
Glassware Safety
1. Chipped or cracked glassware should not be used. Show it to the Instructor.
2. Broken glassware should not be disposed of in a classroom trashcan. There is a special glass disposal container for it.
3. When pouring liquids into glassware, make sure the container you are pouring into is resting on a table at least a hands width from the edge. 17
4. Pour down a glass stirring rod to prevent liquids from splattering.
5. If a piece of glassware gets broken, do not try to clean it up by yourself. Notify the instructor.
6. When inserting glass tubing into a rubber stopper, apply a lubricant like glycerine to the glass and use a twisting motion.
7. Do not place hot glassware in water. Rapid cooling may make it shatter.
Heating Safety
1. Let water baths and hotplates cool down before touching them. Test to see if they are cool enough by bringing the back of your hand close to them.
2. Use tongs and/or protective gloves to handle hot objects. Remember cold glassware looks like hot one.
3. The only type of glassware that may safely be heated is either Kimax or Pyrex.
4. Always point the top ends of test tubes that are being heated away from people.
5. When heating a test tube, move it around slowly over the heating source to distribute the heat evenly.
6. Only glassware that is thoroughly dry should be heated.
Emergency Procedures
Injury Burns
To Do Immediately flush with cold water until burning sensation is lessened.
Injury Cuts, bruises
To Do Do not touch an open wound without safety gloves. Pressing directly on minor cuts will stop bleeding in a few minutes. Apply cold compress to bruises to reduce swelling.
Injury Fainting
To Do Provide fresh air and have the person lie down so that their head is lower than the rest of their body.
Injury the eyes
To Do flush eyes immediately with plenty of water for several minutes. If a foreign object is lodged in the eye, do not allow the eye to be rubbed.Push handle to startthe flow of water!
Position headbetween spigots.
Injury Poisoning
To Do find out what substance wasresponsible for the poisoningand alert the instructorimmediately.
Injury Spills on the skin
To Do flush with large quantities ofwater. For acid spills, applysodium bicarbonate solution.
For base spills, apply vinegar orboric acid.
Lab Safety Equipment
In case of an emergency,you should know thelocation and proper use ofall the safety equipment in the laboratory.Always immediatelyinform the instructor ofany accident.
Fire Extinguishers
It's easy to rememberhow to use a fireextinguisher if youcan remember theacronym PASS,which stands for Pull,
Aim, Squeeze, andSweep.
Safety Shower
Any chemicalspill on a personshould bewashed offimmediately andthoroughly usingthe safetyshower.Pull the chain to startthe flow of water! 31
• Remove all contaminated clothing andstand under the shower.
• Pull the chain to start the flow of water.
• Washing should continue long enough toinsure complete removal of the chemical,at least 15-20 minutes.
Any chemical spill on a personshould be washed offimmediately and thoroughly usingthe safety shower
Sand Ansul and Bicarbonate
ACIDMETAL
Bicarbonate, Sand, AnsulContainers
Located on lab benches are containers ofsodium bicarbonate to neutralize acid spills,plus sand and Ansul containers for smallfires.These work by covering either the spill of acidor the fire with a solid.
Each needs to be cleaned up and disposed ofin a specific manner.
Be sure that the instructor is notified if any ofthese materials have been used.
Special Caution Handling Glassware
Many laboratory accidents involve cuts orpuncture wounds due to impropermanipulation of glassware.
Never force a piece of glasswarewhen constructing experimentalapparatus!
Use proper hand protection and lubricantssuch as glycerin or soapy water whenpossible.
Special Caution-HandlingGlassware
Lubricate glasssurfaces.ProtecthandsNEVER forcethe glassware!
Waste Disposal
Discard waste as needed, duringand at the end of each laboratory period.37
Waste Disposal
• First ask your Instructorwhere/how to dispose ofwaste.
• Never pour anything down thedrain unless you are told to doso.
• A waste bottle will be suppliedfor substance that cannot godown the drain
Waste Disposal
Specificguidelines needto be observedfor wastedisposal.Waste Basket
Paper Products
Paper productsthat do notcontainchemicals canbe placed in thewaste baskets.Waste Basket
Broken Glassware Crock
Broken glass or single-use glassware shouldbe placed in the broken glassware crocks after any disposable contents have been removed.
Solid and liquidchemicals need to beplaced in appropriatecontainers.The exact means will begiven in the labprocedure or specifiedby the instructor.
Solid and Liquid Chemicals
Never rinse chemicals down the drain!
Learning to work safely in thelaboratory is as important aslearning the chemical conceptsand techniques involved in eachexperiment.
Experiment 1
Evaluation of the universal gas constant, R
OBJECTIVES
To use the reaction of magnesium metal with hydrochloric acid to determine the value of the universal gas constant R.
Matarials
Equipments / Quantity / Chemicals / QuantityBurette / 1 / Magnesium ribbon / 30 mg
Top load balance / 1 / Concentrated HCl / 10 ml
500 ml glass beaker / 1
Ruler / 1
Theory
The ideal gas law gives the relation between the pressure (P), volume (V), temperature (T), and the number of moles of gas (n) in volume V:
PV = nRT(1)
R is called the universal gas constant. Eq. 1 is called the ideal gas law because it assumes that there are no attractive or repulsive forces between the gas molecules. For this reason, it can be applied to any gas or gas mixture, independent of the nature of the gas. “Real” gases will show deviations from the ideal gas law, but for most applications such deviations become important only at high pressures or low temperatures. At atmospheric pressure and room temperature deviations from the ideal gas law typically are only 1 or 2%.
In this experiment we will assume that the ideal gas law can be applied to hydrogen gas, and we will determine the value of R by measuring the volume of H2 gas evolved in the reaction of a known mass of Magnesium metal, Mg, with excess hydrochloric acid, HCl.
In the L.atm system, pressure has the units of atmosphere (atm), volume is in L, n in moles and T in Kelvin (K). If we write these units in the gas law:
P(atm).V(L) = n(mol).R.T(K)
We see that the units for the gas constant R are L.atm/mol.K.
In the SI system, pressure has the units of pascal (Pa), volume is in m3, n in moles and T in Kelvin (K). The pressure unit Pa equals N.m−2 (force/area). R will then have the units J/mol.K.
L.Atm.system:R = 0.08206 L.atm/mol.K
SI system:R = 8.314 J/mol.K
In the calculations for this experiment we will use the L.atm system. You will be able to calculate the value of R from your own experimentation, by measuring the values of P and V for a known number of moles of gas evolved, n, in three separate trials, then calculating the value of R as determined in each trial. Obviously, in your final calculation of R, it is important the use consistent units.
The procedure uses the reaction between magnesium metal and hydrochloric acid, resulting in the formation of hydrogen gas:
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
The hydrogen gas evolved will be collected over the dilute HCl solution in an inverted burette. This means that the gas collected will contain H2 but also water vapor, which has a “vapor pressure”, PH2O. The pressure exerted by the H2 will be the atmospheric pressure Patm minus the vapor pressure of water:
PH2 = Patm − PH2O(2)
The vapor pressure of water, PH2O, is given in mm Hg (see the following table).
T (oC) / PH2O (mm Hg) / T (oC) / PH2O (mm Hg)15 / 12.8 / 23 / 21.1
16 / 13.6 / 24 / 22.4
17 / 14.5 / 25 / 23.8
18 / 15.5 / 26 / 25.2
19 / 16.5 / 27 / 26.7
20 / 17.5 / 28 / 28.3
21 / 18.7 / 29 / 30.0
22 / 19.8 / 30 / 31.8
The atmospheric pressure may be assumed to be 1 atm (760 mm Hg) or can be read on a barometer. The temperature T will be the temperature in the laboratory.
A further correction to Patm may be needed to correct for the final liquid level in the burette after the reaction is complete. The correction for the difference in water level between inside the burette and the beaker must be measured in order to correct for the pressure difference. Since the density of mercury (Hg) is 13.6 g/mL, and for water it is 1.0 g/mL, we can directly convert the level difference in mm water to mm Hg:
ΔPlevel correction (mm Hg) = (3)
Of course this ΔP may be positive (when the level in the burette is above the level in the beaker) or negative (when the level in the burette is below the level in the beaker). The final result is:
PH2 = Patm − PH2O − ΔPlevel correction(4)
To convert mm Hg to atm or Pa, and oC to K you need the following conversions:
1 atm = 760 mm Hg
K = oC + 273.15
In this experiment, you will do three separate trials to find the value of R as determined in each trial.
Finally, you will calculate the average value of R from the three trials, and the standard deviation (SD) of the average value.
Raverage = ΣRi/3(5)
SD = (6)
The SD can be expressed as absolute value or as a relative value (%):
SD(%) = (SD(absolute)/Rave)x100%(7)
SAFETY:
PUT GOGGLES ON NOW! Wear your lab coat and glooves
Conc. HYDROCHLORIC ACID CAN HARM YOUR EYES AND CLOTHING, PAY ATTENTION , Handle concentrated HCl in the fume hood only
Hydrogen is highly flammable, so of course no open flames or electrical sparks close to your experiment.
PROCEDURE
- Weigh approximately 25 mg Mg ribbon to the nearest 0.001 g on a top-loading balance.
- Bend the piece of ribbon so that it will fit tightly into a burette (check with your instructor).
- Obtain a 500 mL beaker and fill it with water to approximately 400 mL.
- Obtain a 50 mL burette. Make sure the stopcock is tightly closed. Measure the volume at the bottom of the burette between the stopcock and the 50 mL mark by adding water from a 10 mL graduate cylinder. Record this volume in your notebook (it will be approximately 4-5 ml).Empty the burette again.
- In the fumehood, pour approximately 10 mL concentrated HCl (provided) into the burette. Wash down any acid drops that may stick to the burette wall.
- Push the Mg ribbon into the open end of the burette, to approximately 5 cm from the top. Fill the burette to the top with water.
- Invert the burette in the 500 mL beaker, making sure the Mg stays in place. The top of the burette should be close to the bottom of the beaker.
- The HCl in the burette will gradually sink and diffuse to reach the Mg and start to react. If the Mg breaks free make sure that all will still react. Once all Mg has reacted, make sure that the burette is in an accurately vertical position and record the solution level. Also record the level difference (in mm, not mL!) between the burette and the water in the beaker.
- Calculate the value of R using eq. 1, of course with correct units!
- Repeat this complete procedure two times.
- Calculate the average value and the standard deviation of R from your three experiments.
Evaluation of the universal gas constant, R
Date:………………….Student name:………………………
Course:………………….Team members:………………………
Section:…………………. Instructor: ………………….…………
- DATA:
Trial 1 / Trial 2 / Trial 3
Mass of Mg
Moles Mg
Burette volume above 50 mL mark
Final burette reading (mL)
Volume of gas (mL)
Barometric pressure (mm Hg)
Level difference (burette−beaker) (mm)
ΔP (mm Hg)
Room temperature (K)
PH2O (mm Hg)
PH2 (eq. 4) (mm Hg)
PH2 (atm) = (mmHg/760)
R (L.atm/mol.K
Average value for R
Standard deviation (SD) of R for 3 trials
Relative SD of R, % =
(SD/Rave)x100%
Difference with literature value for R (%)
2. Sample calculation (use data for trial 1)
a)PH2 = Patm − PH2O − ΔP with ΔP = mm level difference/13.6 (mm Hg)
Patm = ______(mm Hg)
PH2O = ______(mm Hg)
ΔP = ______(mmHg)
PH2 = ______(mm Hg) = ______atm
VH2 = ______mL = ______L
b)n = mass Mg (g)/amu Mg =______moles Mg = ______moles H2
c)R = PV/nT R = ______L.atm/mol.K
Experiment 2
Synthesis of Aspirin
OBJECTIVES
In this experiment, you will
- Synthesis the most well-known drug Aspirin.
- Determine aspirin theoretical and practical yield.
- Determine aspirin melting point.
MATERIALS
Equipments / Quantity / Chemicals / Quantity150 ml flask / 1 / salicylic acid / 1 g
Hot plate with M stirrer / 1 / acetic anhydride / 2 mL
stirring bar / 1 / concentrated H2SO4 / 2 drops
Filtration system (Buchner) / 1 / Ice cubes
400 ml beaker / 1
Conical flask (125ml) / 1
Melting point apparatus / 1
THEORY
Most drugs are chemical compounds which are described as "organic compounds" because they are comprised primarily of the elements carbon, hydrogen and oxygen. The present experiment will be the synthesis of a familiar organic compound called aspirin. The common chemical name is acetylsalicylic acid.
Today, aspirin is one of the most widely used, commercially available pharmaceutical drugs in the world. Its properties make it a powerful analgesic (pain reliever), antipyretic (fever reducer) and anti-inflammatory (reduces swelling) drug. Aspirin is not without its faults. It still causes some stomach irritation in some individuals, and it has been estimated that about 1 mL of blood is lost from the stomach lining for each gram of aspirin consumed. Aspirin is known to interfere with normal blood clotting (which actually may be a benefit in preventing heart problems). Reye syndrome, a rare but serious illness has been associated with aspirin, and children and teenagers should not use aspirin for flu like symptoms before consulting a doctor.
Salicylic acid reacts with acetic anhydride according to the following reaction:
MW = 138.12 MW = 102.09 MW = l80.16
The above reaction is an example of an organic synthesis called esterification. Esterification is theacid catalyzed reaction of a carboxyl (-COOH) group and an -OH group of an alcohol or phenolto form a carboxylate ester. In the synthesis of aspirin the -OH group is the phenolic -OH group attached to ring of the salicylic acid. The acetyl group, -COCH3 comes form acetic anhydride, and the reaction is catalyzed by sulphuric acid.
Acetylsalicylic acid is the "generic" name for the compound that is commonly called "aspirin".This reaction is quite simple and gives a good yield of the product. Aspirin, although it is soluble in hot alcohol, is not soluble in water. Consequently, the final product will be filtered from an aqueous solution, and washed with cold water, then air dried.
SAFETY: