CHEM 113.2 Laboratory Safety and Basic Operations Notes
Safety Precautions and the Chemical Laboratory
Safety is the state of being “safe,” derived from the French word “sauf,” meaning protected from harm or undesirable outcomes.
Safety precautions are the most important instructions in this course; failure to observe them may lead to accidents and injuries.
The laboratory is not inherently dangerous, but carelessness causes accidents.
If precautions are followed, the laboratory is safer than everyday environments.
1) Eye protection
Goggles or other OSHA-approved eye equipment must be worn at all times in the laboratory unless the instructor specifies otherwise.
Contact lenses or regular glasses cannot substitute for approved eye protection.
2) Footwear and clothing
Shoes or adequate foot coverings must be worn.
Avoid easily combustible clothing or loose-fitting clothing.
Long hair should be tied back or restrained; use hair nets or style changes to reduce hazard near burners.
3) Protective clothing and safety equipment
Protective laboratory aprons or coats are generally required.
Know the locations of fire extinguishers and other safety equipment (eyewash fountains, showers, fire blankets).
Fire response guidance:
In a minor fire, wet paper towels can smother the fire; inform the instructor.
If clothing catches fire, smother with a blanket or heavy coat or use the laboratory showers; if far from a shower, roll on the floor to extinguish flames. Rolling may also help if a blanket or showers are not immediately available.
If chemicals contact eyes, wash with water at an eyewash fountain for several minutes and report to the instructor.
If chemicals contact skin, wash with water immediately and report irritation.
If chemicals contact clothing, inform the instructor; sodium hydrogen carbonate or other substances may prevent damage to clothing.
If you are burned or injured, inform the instructor; may be directed to health services or a physician.
4) Food and drink prohibition
Do not taste, eat, or drink anything in the laboratory.
5) Reading instructions and cautious heating
Always read instructions carefully; if in doubt, ask the instructor.
Heizing tips:
When heating any material in a glass container, ensure it is borosilicate glass (e.g., Pyrex or Kimax).
When heating materials in a test tube, point the open end away from yourself and others; tilt the tube and heat near the top of the liquid first; never heat the bottom of a test tube containing liquids.
Be careful when inserting glass tubes or thermometers through rubber or cork stoppers; lubricate with water, glycerine, or another lubricant; hold near the stopper; protect hands with a towel. Never force glass tubing or thermometers through stoppers.
Do not use mouth suction to fill pipets; use a pipet bulb and have the instructor demonstrate proper technique if unsure.
Exercise care with odors of gases or liquids; use a fume hood whenever releasing noxious fumes.
6) Working with others
Do not work alone in the laboratory.
In classes with experienced students, a group may be allowed to work unsupervised, but generally no persons other than class members are allowed without explicit instructor permission.
7) Prohibited and general conduct
Never perform unauthorized experiments.
Keep tabletops clean; even a small-looking drop could be a strong acid or base and damage clothing or harm peers.
If you need to obtain liquids from the stockroom, use a plastic bucket to transport them.
Unless directed otherwise, never return chemicals to reagent bottles or containers; discard surplus reagents as instructed.
Many organic reagents are flammable; keep them away from flames and do not pour flammable liquids down sinks (they may accumulate and explode in pipes). Follow any specific disposal instructions given for organic liquids.
Common Laboratory Operations and Concepts
Common operations used daily in chemistry labs: volume measurement, weighing, heating, evaporation, precipitation, decantation, filtration, and centrifugation.
Some laboratories require more equipment; others require little to none. See Figure 1 for common apparatus and equipment (referenced in the text).
A. Volume Measurement
Volume is the amount of space taken by a substance; capacity is the ability to hold a substance.
Glassware readings:
Medicine droppers, beakers, and Erlenmeyer flasks provide approximate volumes.
Precision glassware (volumetric flasks, pipets, burets, and graduated cylinders) provide more accurate readings.
Reading technique:
Hold the glassware vertically at eye level.
Read the meniscus—the curved surface of the liquid; there is a flat portion in the center.
Determine the volume by the position of the flat center portion relative to the calibration marks.
Cleanliness: Glassware must be clean to prevent chemical contamination, and to ensure proper drainage so the delivered volume matches the calibration marks.
Burets: Constructed to measure volume more precisely than a graduated cylinder.
The zero mark must be at the initial reading; the delivered volume is the difference between final and initial readings:
Ensure no drops hang from the buret tip before and after delivering liquid.
After delivering a volume, touch the tip to the wall of the receiving vessel to remove last drop.
Pipets (volumetric): For accurate, repeated measurements.
Use a rubber bulb to draw liquid past the ring mark, then stop suction with a fingertip, drain to the ring mark, and transfer to a receiver.
Allow the liquid to drain for about 10 seconds for proper wall drainage, then touch the tip to the receiver wall to remove the last drop.
Pipet technique while pouring from bottles:
Hold the pipet vertically; use a stirring rod at the vessel mouth to direct flow along the side to avoid splashing.
B. Weight Measurement
Common weighing devices: platform balance, single-pan balance, top-loading balance, analytical balance.
Weighing rules:
Familiarize yourself with the balance type before weighing.
If there is difficulty operating the balance, consult the instructor; do not adjust.
Do not move or relocate the balance.
Do not interchange balance pans; each pan is calibrated for its balance.
Never weigh chemicals directly on the balance pan; use a watch glass or weighing paper; clean spills.
Weigh volatile or corrosive samples in stoppered containers.
Do not weigh objects not at room temperature.
Arrest the balance beam before removing the weighed object from the pan.
Weighing method:
Weigh the container (tare weight), then add the sample and weigh together (gross weight).
Net weight = Gross weight − Tare weight.
See table references (e.g., table 2.2) for rule details.
C. Heating of Liquids
In a test tube:
Hold with a test tube holder at a slant.
Point the mouth away from yourself and others.
Move the tube gently side to side for even heating.
Avoid heating the glass above the liquid; cooler liquids may crack hot glass when they meet.
Do not heat the bottom of a test tube containing liquids.
In a beaker:
Support the beaker about 5–7 cm above the burner by an iron ring on a stand or a tripod.
Place a wire gauze between the beaker and the heat source to distribute heat evenly.
D. Precipitation
When substances in a solution interact to form a solid that is soluble or only slightly soluble in the solvent, precipitation occurs.
Separation of the solid from the liquid can be done by decantation, filtration, or centrifugation.
E. Decantation
Separation of a solid and liquid by pouring off the liquid while leaving the solid behind.
Allow the mixture to settle; pour off the liquid down a stirring rod, leaving the solid behind.
The liquid above the precipitate is the supernatant liquid.
Decantation is not always convenient, especially if the precipitate does not settle easily.
F. Gravity Filtration
Filtration separates a solid-liquid mixture by passing it through a barrier with fine pores (filter paper).
Filtrate is the clear liquid passing through; the precipitate remains on the filter paper.
G. Centrifugation
Rapid separation of solids and liquids using centrifugal force, separating based on size, density, viscosity, rotor speed, and geometry.
Dense components move outward from the axis; less dense components move toward the axis.
During operation, ensure tubes are crack-free and sealed; balance the rotor; allow complete stop before opening.
H. Evaporation
Evaporation (vaporization) is when molecules escape from a liquid surface into the gas state due to kinetic energy.
The residue remaining after evaporation is the material left behind.
Evaporation is typically performed in an evaporating dish over a burner or hot plate.
Materials List (from Procedure Context)
20.0 mL graduated cylinder
3 M NaOH
3 M FeCl3
10.0 mL pipet
Filter paper
Evaporating dish
Tripod
Aspirator
Clay triangle
50 mL beaker
Funnel
Platform balance
Stirring rod
Hot plate
Watch glass
Crucible tong
Wash bottle
Medicine dropper
Procedures and Experimental Steps
A. Measuring Volume
a) Measure 20 mL water using a graduated cylinder and show it to the instructor.
b) Measure 7.50 mL of water using a pipet and show it to the instructor.
B. Measuring Weight
Weigh out 10.0 g of sand and show it to the instructor.
C. Precipitation
Measure 1.0 mL of 3 M ferric chloride (FeCl3) and place it in a 50-mL beaker.
Measure 90 mL of 3 M sodium hydroxide (NaOH) and mix with FeCl3 in the beaker.
Observe the formation of a precipitate.
Allow the precipitate to settle and add NaOH drop by drop until no more precipitate forms.
Divide the solution into two equal parts; save for parts E and F.
D. Decantation
Weigh an evaporating dish and record the weight.
Decant the supernatant liquid (from part C) into the evaporating dish, saving for part F, ensuring no precipitate accompanies the liquid.
Add 2.0 mL distilled water to the precipitate left in the beaker. Save for part F.
E. Filtration
Prepare a piece of filter paper by folding it in half along one diameter, then quarters; tear a corner and open into a cone.
Weigh the filter paper; insert into funnel; moisten with distilled water; press gently to remove air bubbles.
Support the funnel on a rack; place the receiver under the funnel with the tip touching the wall.
Pour the mixture from part C through the paper using a stirring rod; do not allow liquid level to rise above the top of the paper.
Rinse/filter the solid on the paper with a minimum amount of distilled water; save filtrate for part F.
Remove and dry the filter paper on a watch glass and weigh.
F. Evaporation
Evaporate the supernatant liquid from part D and the filtrate from part E to recover dissolved sodium chloride.
Place the evaporating dish on a hot plate; when all water has evaporated, cool to room temperature and weigh.
Results and Discussion (Typical Outputs)
Measuring Volume: a) Using a pipet; b) Using a graduated cylinder.
Measuring Weight: a) Tare weight (weight of container); b) Gross weight (container with sample).
Precipitation: a) Color of FeCl3 solution; b) Color of NaOH solution; c) Color of precipitate.
Decantation: a) Color of supernatant liquid.
Filtration: a) Weight of filter paper; b) Weight of filter paper + precipitate after drying; c) Weight of precipitate; d) Color of filtrate.
Evaporation: a) Weight of evaporating dish; b) Weight of dish + residue after cooling; c) Weight of residue; d) Color and e) Texture of residue.
Guide Questions (for quiz and lab report submission)
1) What are the safety precautions in handling organic chemicals?
2) State the proper way of heating liquids using a test tube.
3) Which is more accurate for volume measurement: a graduated pipet or a graduated cylinder?
4) Which is more efficient for separating solids from liquids: filtration or decantation? Why?
5) Write the balanced chemical equations involved in:
a) Precipitation
b) Evaporation
6) What is the chemical composition of:a) The filtrate
b) The residue
7) If the precipitate size is smaller than the filter paper pores, the paper cannot retain it. Give two alternative separation methods to overcome this.