A Qualitative Analysis Experiment

Friday, July 15, 2011

Experiment 5

Experiment 5

Topic      : Volumetric analysis – Stoichiometry

Purpose  : To determine the exact concentration of a monobasic acid, HX.

Material :  i) Monobasic acid, HX.

                  ii) Solid sodium hydroxide,NAOH.                    

Apparatus :  i) One volumetric flask 250ml and stopper.

                      ii) Electronic balance ±0.01g

                      iii) Three tiltration flask.

                      iv) One 25 cm³ pipette and pipette filler

                      v) One 50 cm³  burette.

                      vi) One retort stand and clamp.

                      vii) One white tile.

                      viii) One wash bottle filled with distilled water.

Theory  :  Neutralization process occurred between acid and base. Then H+ ion from acid react with OH־ ion from the base to form H2O.

Procedure  : a) i) A piece of filter paper is weighted using the electronic weight.

                          ii) A spoon of solid sodium hydroxide,NAOH is taken from the container

                               using spatula and weighted.

                          iii) The reading of the measurement is recorded.

                          iv) The sodium hydroxide,NAOH is then put into the beaker .

                          v) A little amount of distilled water is filled into the beaker and stirred using a glass  rod to dissolve the solid sodium hydroxide , NaOH .

                          vi) The solution is then transferred into 250cm³ volumetric flask

                          vii) Using the 25 cm³ pipette to pipette 25 cm³ of NAOH solution into the

                                 titration flask.

                          viii) Monobasic acid, HX solution is poured into the 50ml burette.

                          ix) Titrate the solution as well.

                          x) Record your readings in the table below.

                          xi) Repeat the tiltration as many as you think necessary to achieve

                               accurate result.

Results       : b)  Record your tiltration reading in the table below :


Third          I  Average
 Final reading/cm
11.40          I  11.36
Initial reading/cm
0                 I   0
Volume of KA1/cm
11.40          I    11.36

( i )   25.0 cm³ of   KA 1  require  20.5  cm³ of  KA 1  for a complete reaction.

( ii )  Calculate your average tiltrate value showing the suitable tiltrate values.

             Average volume :   21.2 + 20.3 + 20.0   cm³
                                           = 20.5 cm³

              Average volume  =  20.5 cm³

Calculation :  Mass of filter paper : 0.0 g

                        Mass of filter paper and solid sodium hydroxide : 4.0 g

                        Mass of solid sodium hydroxide : 4.0 g – 0.0 g
                                                                              = 4.0 g

                        Relative molecular mass of NaOH  = 23.0 + 16.0 + 1.0
                                                                                = 40.0 g mol־¹

No. of mole of NaOH = ___4.0 g___                  Molarity of NaOH = _0.1 mol_                 
                                           40.0 g mol־                                                    0.25 dm³

                HX  +  NaOH    NaOH  +  H2O
                From the equation, 1 mole of HX react with 1 mole of NaOH.
                Concentration of monobasic acid, HX  4  M1V1 = M2V2
                                                                                    M2 = 0.4 × 25 
                                                                                          =  0.49 mol dm־³                                                                       
Conclusion  :  20.5 cm³ of HX react with 25.0 cm³ of  0.40 moldm־³ of NaOH to produce
                        water and salt. The concentration of HX obtained through calculation is
                        0.49 mol dm־³.
 Comment    :  The value obtained is slightly different from the theory because there is
                        some parallax error when the experiment is carried on.

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