Laboratory TechniquesSection 3LChemistry I & II

Laboratory TechniquesTo ensure safety, correct laboratory techniques should be used at all times!!

Refer back to this section of notes any time you are unsure of proper laboratory technique.

If proper technique/lab safety is not followed, you will receive a violation notice which could result in a warning, loss of points, and/or loss of all laboratory privileges.

Before you beginAlways read the label on a reagent bottle before using its contents.Always wear safety goggles when handling chemicals.Never touch chemicals with your hands.Never return unused chemicals to their original containers.To avoid waste, do not take excessive amounts of reagents.

NFPA Diamond LabelNational Fire Protection Association diamond indicates flammability, reactivity, health concerns, and other potential hazards associated with the reagent.Numbers are used to rate potential hazards on a scale from 0 (least hazardous) to 4 (most hazardous)

NFPA Diamond Level

Material Safety Data SheetAdditional information can be found about each chemical on a MSDS (see example MSDS).It is divided into 16 sections, containing 4 types of informationCritical Emergency InformationSubstance identityManufacturerHazardous componentsIdentification of the hazards

Material Safety Data SheetEmergency Response MeasuresFirst aidFire-fightingAccidental ReleasePersonal Protection and Exposure MeasuresHandling and storagePersonal Protection EquipmentExposure controlsPhysical and Chemical PropertiesStability and reactivity of the substance

Material Safety Data SheetOther useful informationToxicological and ecological effectsDisposal considerationsTransport and regulatory informationMiscellaneous information

The layout and exact contents of MSDSs vary from supplier to supplier.

Techniques Used in the Lab

Pouring LiquidsUse the back of your fingers to remove the stopper from the reagent bottle.Hold the stopper between your fingers until the transfer is completeDo not place the stopper on the lab station.Grasp the container from which you are pouring with the palm of your hand covering the label.

Pouring LiquidsWhen you are transferring a liquid to a test tube or graduated cylinder, the container should be held at eye level.Pour the liquid slowly until the correct volume has been transferred.When you are pouring a liquid from a reagent bottle into a beaker, the reagent should be poured slowly down a glass stirring rod.

Transferring LiquidsUsing a dropper bottleNever lay the dropper on any surface.Be sure the dropper never touches your container or its contents.Using a Beral or Pasteur PipetDo not pipet directly from the reagent bottle unless instructed to do so.Instead, pour some of the liquid into a labeled container and pipet from your containerDo not touch the container or its contents with the tip of the pipet

Mixing LiquidsTo dilute concentrated liquids with water, ALWAYS add the concentrated reagent to the water slowly.This is especially important to follow when adding a concentrated acid to waterBecause of the large amount of heat generated by this combination splattering can occur.

Mixing a Solid and a LiquidAdd the solid to the liquid while stirring continuously.Add the solid in small amounts, unless instructed otherwise.

Filtering a MixtureSometimes it is necessary to separate a solid from a liquid filtration is necessary.Fold a paper circle in half and then in quarters.Open the folded paper to form a coneOne thickness of paper on one side and three thicknesses on the other

Filtering a MixturePut the paper cone in a filter funnel.Place the funnel in an iron ring clamped to a ring stand.Moisten the filter paper with a small volume of distilled water and gently press the paper against the sides of the funnel.Place a beaker beneath the funnel to collect the filtrate.The tip of the funnel should touch the inside surface of the beaker and extend about one inch below the rim.

Filtering a MixtureDecant the liquid from the solid by pouring it down a glass stirring rod into the funnel.Be careful to keep the liquid below the top edge of the cone of filter paper at all times the liquid must not overflow.Use distilled water from a wash bottle to wash the solid into the filter.

Filtering a MixtureWhen the filtration is complete, wash the solid residue on the filter paper with distilled water to remove traces of solvent dry the solid.If the filtrate contains a dissolved salt, it may be recovered by evaporation if desired.

Heating Liquids Heating a liquid in a test tube:Adjust the gas burner to produce a gentle blue flameFill a test tube one-third full with the liquid to be heated.Grasp the test tube with a test tube holder, near the upper end of the test tube.Hold the test tube in a slanting position in the flame, and gently heat the tube a short distance below the surface of the liquidShake the test tube gently as it is being heated, until the liquid boils or reaches the desired temperature.

Heating LiquidsCAUTION:

NEVER point the open end of a test tube you are heating either toward yourself or anyone working nearby.

NEVER heat the bottom of the test tube.

Heating LiquidsHeating a Liquid in a Beaker (assembling a water bath)Fasten an iron ring securely to a ring stand so that it is 2-4 cm above the top of a gas burner placed on the ring stand base.Place a beaker half-filled with water on a wire gauze resting on the iron ring.Light your gas burner and adjust it to produce a hot flame.Place the burner beneath the wire gauze.A hot plate can also be used in place of the gas burner.

Heating LiquidsCAUTION:

NEVER heat plastic beakers or graduated glassware in a burner flame.

NEVER let boiling water boil dry add water to it as necessary.

Measuring VolumeVolume measurements can be accurate or approximate.Most volume measures in the lab are made using equipment calibrated in milliliters.Although some beakers have graduation marks, these marks are designed only for quick, rough estimates of volume.Accurate volumes must be measured with pipets, burets, or volumetric flasks.

Measuring VolumeUsing a graduated cylinder:A volume measurement is always read at the bottom of the meniscus curved surface where the water comes in contact with the cylinder wallsMeasurements should always be one place more than the graduation marks on the cylinder.Example: 100mL broken up into 1mL increments read to 0.1mLAlways estimate between the smallest marks

Measuring VolumeUsing a pipetA pipet is used to accurately measure and deliver volumes of liquids.Two Types:Volumetric has single calibration mark and delivers the volume printed on the bulb of the pipet at the temperature specified.Graduated has calibration marks along the length of the pipet.

Measuring VolumeUsing a volumetric pipet (more accurate than graduated pipet)Place the tip of the pipet below the surface of the liquid to be dispensed.Compress a pipet bulb and press the hole in the bulb against the upper end of the pipet.Never push the pipet bulb over the end of the pipetNever fill a pipet by applying suction with your mouth.

Measuring VolumeSlowly release pressure on the bulb so that liquid is drawn into the pipet to a level about 2 cm about the calibration markRemove the bulb and simultaneously place your index finger over the end of the pipetKeep your index finger pressed firmly against the end and withdraw the pipet from the liquid and carefully wipe the outside with a paper towel.

Measuring VolumeSlowly reduce the pressure on your finger to allow the excess liquid to drain into a waste container until the bottom of the meniscus is at the calibration mark.Deliver the remaining liquid in the pipet to the designated container.Let it drain completely.Wait 20 seconds, and touch the tip of the pipet to the side of the flask or surface of the liquid. A very small amount will remain in the pipet.

Measuring VolumeUsing a BuretA buret is a long, narrow, calibrated tube with a device at one end to control the flow of liquid from the buret.These measurements are more precise than those made using a pipet.Burets differ in the type of flow-control device, or valve, that is usedTapered glass stopcock at the end of a glass barrelTeflon stopcock attached to glass/Teflon barrel

Measuring VolumeHow to use a buret:Before using a buret, check to see that the stopcock is liquid tight by closing the stopcock and filling the buret with water report any leaksBegin by rinsing the buret three or more times with small portions of the solution to be used in the buret.Dispose of the rinses as specified

Measuring VolumeClamp the buret vertically to a ring stand.Close the stopcock and use a short-stem funnel to slowly fill the buret with the sample solution.Fill the buret to above the zero calibration mark at the top. Remove the funnel

Measuring VolumePlace a discard beaker under the stopcock, open the stopcock, and drain the solution until the meniscus is at, or slightly below, the zero calibration mark.To remove the hanging drop, touch the wet inside wall of the beaker with the buret tip.Replace the discard beaker with a flask that you want to dispense the liquid into.

Measuring VolumeWhen using a buret with a Teflon stopcock, operate the stopcocks with either hand without the risk of the stopcock slipping out.Glass stopcocks should be operated with the hand on the opposite side of the buret barrel from the stopcock, to avoid pulling the stopcock from the barrel.

Measuring VolumeDrain the solution from the buret relatively slowly.After you have drained the desired volume, close the stopcock.Touch the inner wall of the flask to the buret tip to remove the hanging drop.Use distilled water from a wash bottle to rinse the drop into the liquid in the flask.

Measuring VolumeMaintaining the buretTeflon stopcocks do not need lubrication, but glass stopcocks require a thin film of stopcock greaseTo lubricate the glass stopcock:Carefully remove the stopcock from the barrel and remove any old grease.Place a small amount of grease on the stopcock surface avoiding the area near the hole.Insert the stopcock into the barrel and rotate several times.

Measuring VolumeUsing a volumetric flaskVolumetric flasks are calibrated to contain a specified volume.The single calibration mark is located on the narrow neck to allow filling to a reproducible volumesThey are used to prepare solutions in two general ways:

Measuring VolumeDissolving a solid solute to make a solution of a definite volume.Weigh the solute and dissolve in the minimum amount of solvent in a clean beakerUsing a funnel, transfer the solution to a volumetric flask.Rinse the beaker with a small amount of the solvent and transfer the rinse through the funnel into the flask.

Measuring VolumeQuantitative dilution of a concentrated solutionUse a pipet to transfer an accurately measured sample of the concentrated solution to the volumetric flaskWith either procedure, add more solvent to the flask until it is about 2/3 full, while slowly swirling the flask to agitate the solution.

Measuring VolumeContinue slowly adding more solvent until the liquid level is just below the calibration mark.Stopper the flask and thoroughly mix the solution by inverting the flask end over end.Use a small dropper or pipet to add the final amount of solvent needed to align the bottom of the meniscus with the calibration mark.Stopper the flask, invert to mix, and transfer to a storage container.

Using a Gas BurnerIdentify the model of burnerTwo Types:Bunsen Burner has adjustable air ventsTirrell Burner has adjustable air vents and a gas control valve in its base.For proper procedure see:Lab: Lighting a Gas Burner

Using a Hot PlateA hot plate is an electrical device that is particularly useful for experiments where an open flame is prohibited.A dial or knob controls the hot plate temperature.

Heating a SolidPorcelain crucibles are used for heating solids to thermally decompose the solids or to heat them to dryness.The empty crucible should first be heated to drive off any moisture. Allow to cool.Place the solid to be heated into the crucible.To heat the sample and not allow it to react with the atmospheric oxygen, insert the covered crucible upright in the clay triangle with the cover on straight.To hear the sample and allow it to react with the atmospheric oxygen, tilt the crucible slightly in the clay triangle, and use crucible tongs to position the cover so it is slightly ajar.