EXPERIMENT 1 BASIC LABORATORY LABORATORY TECHNIQUES
INTRODUCTION: Chemistry is an experimental science . It depends u pon careful observation and the use of good laboratory techniques . Most of the experiments in the chemistry laboratory involve quantitative analytical procedure . It involves the use of common glassware for example burette , pipette , volumetric flask , etc . Glassware are used to measure the volume of solutions at certain temperature . he volume of a liquid changes ch anges with temperature . o get the accuracy , the apparatus have to be calibrated before being used . Mistakes and errors can happen during an a n experiment . ! mistake is a blunder or unintentional action with measurement . "rror may be either systematic or random . ! systematic error can happen when an apparatus which is not calibrated is used . he measurement will always be too large or too small . ! systematic error will influence the accuracy of a measurement , that is the agreement between a measured value of a quantity and its true value . ! random error will be the evidence undesirable consequence . "rror on the other hand , account for the range of values obtained from successive measurements of the same quantity , even though there was no mistake in any of the whean a measuring device , even a very accurate one , is used a number time to make the same measurement . #oth errors can be reduced by using calibrated apparatus and by being careful when conducting experiments . Volumetri Volumetri !l"#$
! volumetric flask flask is a glassware designed to deliver de liver the standard solution at precise known volume of liquid at given temperature . he actual volume of liquid in the flask can be determined by weighing the flask when it is empty and when it is filled with distilled water . he difference between both readings is equal to the mass of water . he volume of water in the flask can be calculated ca lculated by referring to able $ . %olumetric %olumetric flasks are used to make solutions of known k nown concentration by the dissolution of a known mass of solid or the dilution of a more concentrated solution . #efore use , always wash the flask and then pre&rinse with a solvent . 'ome frequently used volumes in chemistry laboratory are $(.(( , )*.(( , *(.(( , $((.((, and )*(.(( m+ flasks . !t !t times the eros to the right of the decimal point are omitted .-owever , these eros must a lways be considered in calculations , as they indicate the accuracy of the volume measurement .
Pi%ette
! pipette is a glass vessel that is constructed and calibrated so as to deliver a precisely known volume of liquid at a given temperature . ransfer and Mohr pipettes are two types of common pipette usually used in the laboratory . ! transfer pipette is calibrated to deliver only one volume , whereas a Mohr pipette is graduated so that it can deliver any an y volum usually to the nearest tenth of a millilitre / up to maximum volume . ransfer pipettes come in many sies , but * m+ , $( m+ , )( m+ , and )* m+ pipette are usually used in the chemical laboratories . Common volumes of Mohr pipette are $ m+ , * m+ , and $( m+ volume . he correct use of a pipette requires considerable manipulatoryskill . 'tep&by&step 'tep&by&step procedures for correct usage are 0 $. Clean and and rinse rinse the pipette pipette with with tap tap water , then distil distilled led water water . ). 1inse 1inse the the pipett pipettee with with the solu solutio tion n to be used used . 2. Insert Insert the pipette pipette into into the solution solution and suck suck in about about $ to ) cm above the the etched line line on the pipette , by using pipette filler filler or suction bulb / 3. 4rain excess excess solution solution into into a waste container container until the the bottom of the the meniscus meniscus coincides coincides with etched line *. !llow the the liquid liquid in the pipette pipette to drain drain into into the flask flask to be used in in the experiment experiment .ouc .ouch h off the last drop do not blow the remaining liquid from the pipette . he pipette is calibrated to deliver the correct volume with this liquid remaining in it /. he actual volume of a solution pipette volume / can be measured by weighing the solution that has been transferred using that pipette . 5rom the density of the solution , we can calculate the volume of solution pipette volume / . Burette
! burette orburet / is a vertical cylindrical piece of laboratory glassware with a volumetric graduation on its full length and a precision tap , or stopcock , at the bottom . It is used to dispense known amount of a liquid liquid reagent in experiments for which precision is necessary , such as a titration experiment . #urettes are extremely accurate & *( m+ burette has a tolerance of (.$ m+ class #/ or (.(6 m+class ! / . he difference between initial and final volume is the amount dispensed . he spacing between the lines will allow you to estimate the volume to the nearest (.($ m+.hus , typical burette readings would be two decimal points eg 7.23 7 .23 m+ or $8.6( Ml reading such as 7.2 m+ or $8.6 m+ are not acceptable . he following are steps which will help you to have a burette that operates as it should 0
$. Clean and and rinse rinse the burette burette with with tap water water , then then distill distilled ed water water . ). 1inse 1inse the the burette burette with with about about *&$( *&$( m+ of of soluti solution on .
2. 5ill the the burette burette above the ero ero mark with with the stop stop cork closed closed . 9pen the the stopcock stopcock fully fully so that the liquid drains rapidly to release air bubb le at the tip of the burette . 4rain the liquid until the meniscus rests at a certain number , eg $ m+ marks or ( m+/. 1ead the burette to two decimal places with your eyes at the same level at the meniscus . 3. o obtain the the volume of the solutio solution n liquid liquid / that you use in titrati titration on , subtract subtract the initial initial reading from the final reading . o calibrate calibrate the burette , transfer several volumes of solution from the burette and weigh a accurately.5rom accurately.5rom the density of the solution , we can calculate the volume of solution that has been transferred.
T"&le 1'1 : De(#it) *+,mL- o. /"ter "t V"riou# Tem%er"ture*0C-
Tem%er"ture *0-
De(#it) o. /"ter *+,mL -
)) )2 )3 )* )6 )8 ): )7 2( 2*
$.((2) $.((23 $.((28 $.((27 $.((3) $.((3* $.((38 $.((*( $.((*2 $.((*7
OBECTIVES: o learn learn the qualitative and quantitative quan titative aspects of common laboratory equipment. o expose students to the factors that affect the accuracy of an experiment,
APPARATUS: !nalytical balance, burette, pipette )( m+ or )* m+/, volumetric flask )* m+/, conical flask. beaker *( m+/, and thermometer.
CHEMICAL: 4istilled ;ater
PROCEDURE: $. Calibr Calibrati ation on of of volum volumetr etric ic flas flask k a. Clean and and dry a )* m+ volumetric volumetric flask flask and and weigh accurately accurately using using analytical analytical balance. 1ecord the weigh. b. 5ill the volumetic flask with distilled distilled water and weigh again use the same balance/. 1ecord the weigh. c. 1ecord 1ecord the the tempera temperatur turee of the disti distille lled d water. water. d. 5rom abl ablee $.$ , determine determine the actual actual volume volume of the volumetri volumetricc flask. flask.
). Cali Calibr brat atio ion n of of pip pipet ette te a. Clean and and dry a *( m+ beaker and and weigh accurately accurately using using analytical analytical balance. balance. 1ecord the weigh. b. Clean a pipette )( m+ or )* m+/ and rinse with distilled distilled water. c. 5ill the the pipette pipette with distil distilled led water water using the the procedures procedures that that have been discus discusss in the introduction part. d. 4rain the the distill distilled ed water into the the beaker and weigh weigh again. again. 1ecord the weigh. weigh. e. 1epeat step step &3 one more more time and and record record the temperatur temperaturee of the distill distilled ed water. water. f. 5rom 5rom table table $.$ , determ determine ine the the actual actual volume volume of the the pipett pipette. e.
2. Cali Calibr brat atio ion n of of bur buret ette te a. Clean and and dry a *( m+ beaker and and weigh accurately accurately using using analytical analytical balance. balance. 1ecord the weigh. b. Clean and rinse a burette using distilled water and the fill in the burette with with water until the ero mark. make sure there are no bubbles in the tip of the burette/. c. 4rain * m+ of the water water from from the the burette burette into into the beaker beaker and weigh weigh as soon as possible. 1ecord the weigh. d. 1epeat step step c/ by draini draining ng water from from the burette burette until until the the following following burette burette reading reading become $( m+, $* m+, and )( m+. "ach time * m+ distilled water is added from the burette/. 1ecord the weigh water < beaker/ every time after adding * m+ water. water. e. 5rom abl ablee $.$ , determine determine the actual actual volume volume for every additi addition on of * m+ of distille distilled d water.
CALCULATIONS:
QUESTIONS:
$. -ow do you overcome overcome or reduce reduce the problem problem of random random error error and systemati systematicc error while while doing an experiment= ). In what situati situation on do you use a volumetri volumetricc flask, flask, conical flask, flask, pipette pipette and and graduated graduated cylinder= "xplain your answer from the accuracy aspects of these apparatus. 2. "xplain "xplain how to read read a burette. burette. ;hat are are factors factors to be consider considered ed when using using a burette= burette=
DISCUSSION:
Interpret data results in the context of the specific question you set out to address in this study. Consider the following issues0 a. ;hat ;hat did did you you expect expect to find find,, and and why= why= b. -ow did your results compare with those expected= 'tate your expectations explicitly, explicitly, and back up your statements with a reference. c. +ist any any weaknesses weaknesses in the experim experimental ental design design and and how these these weaknesse weaknessess may have have affected your results. 'ince your laboratory investigation was sub>ect to limitations of time and facilities, you did not do a ?perfect@ experiment. It is important for you to understand and acknowledge this in your conclusion. !lso, consider how you might be able to get more specific and more reliable results by changing certain aspects of the experiment.
CONCLUSION:
