Keeping drops of phenolphthalein indicator solution. 2. Titrate

Keeping up the standardsThe purpose of this assignment is to undertaketitrations and colorimetry to determine the concentration of solutions. A keypart of the job will be making and testing standard solutions using colorimetryand titrations. This will be carried out whilst making sure the equipment iscalibrated and also the equipment and chemicals are safety checked. I will alsobe making and testing standard solutions using colorimetry and titrations.Colorimetry is a way to find the concentrationof coloured compounds in a solution by using a colorimeter; titrations are acommon lab method used as analysis in order to find an unknown concentration ofan element.TitrationsApparatus:·        Goggles·        Bench Mat·        100cm3 beaker·        250cm3 beaker·        250cm3 conical flask·        250cm3 bulb pipette·        Pipette filler·        Burette·        Burette stand and holder·        Plastic filter funnel·        White tile·        Teat pipette·        Access to: your standard sodiumcarbonate solution dilute hydrochloric acid to standardise phenolphthaleinindicator solution methyl orange indicator solutionMethod:1.

      Transfera 25cm3 portion of the sodium carbonate solution to a 250cm3 capacity conicalflask. Add a few drops of phenolphthalein indicator solution.2.      Titratewith the hydrochloric acid. The end-point of the titration is when the solutionjust changes from pink to colourless. Note the titre, and then add a few dropsof methyl orange.3.

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      Titratewith the hydrochloric acid. The end-point of the titration is when the solutionjust changes from yellow to red. Note the second titre.

4.      Repeatsteps 1-3 until they are the same or within 0.1 cm3. Tabulate your titrationsas described in The Burette sheet.You will need two sets of tables.5.      Aftertidying away, do the calculations described overleaf.Photographs of method:        Step1(HCl)                SodiumCarbonate     Add phenolphthalein     Add methyl orange           Mix with HClCalculations:Calculate the Mr of Na2CO3.

Ar(Na)=23 Ar(C)=12  Ar(O)=16Look back at the accurate mass of sodiumcarbonate you used in the last practical. Using your answer to step 1,calculate the No. of moles of Na2CO3 that you dissolved in 250cm3 of waterduring Volumetric Analysis 1.Using your answer to step 2 to calculate thenumber of moles of Na2CO3 in the 25cm3 transferred to the conical flask.Stage1 – Phenolphthalein:Na2CO3(aq)+ HCL(aq)  NaHCO3(aq) + NaCl(aq)M = 0.07*0.025 = 0.00175MRatio = 1:1C = 0.

0175/0.014525 = 0.11MStage2 – Methyl Orange:NaHCO3(aq)+ HCl(aq)        NaCl(aq) + CO2(g) +H20(l)M = 0.0780.

025 = 0.00175MRatio = 1:1M = 0.0175/0.014525 = 0.11MResults:1. Phenolphthalein indicator (first part ofeach run) Burette reagent Approx.

  0.075M hydrochloric acid Conical flask Standard sodium carbonate solution Indicator Phenolphthalein     Run 1 Run2 Run 3 Run 4 Final volume (cm3) 16 16 14.5 15.3 Initial volume (cm3) 0 0 0 0  2.

Methyl orange indicator (second part ofeach run) Burette reagent Approx.  0.075M hydrochloric acid Conical flask Standard sodium carbonate solution Indicator Methyl orange       Run 1 Run 2 Run 3 Run 4 Final volume (cm3) 14.

2 14.5 15 14.4 Initial volume (cm3) 0 0 0 0  Observation(s):·        Colour change volumes were recordedwhen the colour change was strong and not when the colour was in transition ofchanging and or faint.·        Colour changes to pink when you addphenolphthalein on NaCl.·        Colour returns to uncoloured when youadd HCl.·        Colour changes to yellow when you addMethyl orange.·        Colour returns to pink when HCl isadded.

ColorimeterHowto operate a Colorimeter:1.      Turnthe instrument on for at least 5 minutes before using it to allow it tostabilize itself2.      Usethe most appropriate filter for analysis and insert it into the light path3.      Usea clear solution and zero the instrument with it making sure the clear side ofthe cuvette are in the lights path4.      Placeyour solution in the colorimeter and read the solutions absorbance.

If theabsorbance is stated as ‘over range’ then the sample must be diluted so you canreceive a reading5.      Atregular intervals, you can use the clear sample in order to make sure themachine is still calibratedApparatus:·        Copper Sulphate·        Distilled Water·        Colorimeter instrumentMethod:1.     After been given a solution of coppersulphate (0.

5M) you need to produce 5 different concentrations will be 0.0,0.1, 0.2, 0.3 and 0.4M.

2.     Fill up a measuring cylinder of 10Cm3with a mixture of copper sulphate and distilled water of any one of theconcentrations above.Table: Concentration 0.5M 0.4M 0.3M 0.2M 0.1M 0.0M Volume of water in cm3 0 2 4 6 8 10 Volume copper sulphate in cm3 10 8 6 4 2 0 Final volume in cm3 10 10 10 10 10 10  Results: Concentration of copper sulphate   Absorbance 0.0 M 0.00 0.1 M 0.31 0.2 M 0.57 0.3 M 0.86 0.4 M 1.13 0.5 M 1.38         


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