Belair High School Caribbean Advanced Proficiency Examination
Name: _______AbbyshayGayle_________________ Lab Write-up Sheet
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50286539-Guidelines-for-Module-One-Essay-Cape-Communication-Studies
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Lab Write-up Sheet Date: ___/___/___ Lab No. 3 Title: Determination of the concentration of NaOH using HCl Aim: To determine the concentration of sodium hydroxide using an accurately known solution of HCl. Apparatus: Burette, pipette pump, pipette, retort stand, volumetric flask, conical flask, methyl orange indicator, dropper, 0.1mol dm3 HCl, NaOH solution. Introduction: Titration is a technique where a solution of known concentration is used to determine the concentration of an unknown solution. NaOH, a base, and HCl, an acid, are reagents in this experiment; they neutralize each other to form a salt and involves the combination of H+ ions and OH- ions to generate water (undergo a neutralization reaction). The concentration of the HCl acid is accurately known, therefore, it can be used to determine the concentration of sodium hydroxide. Considering that NaOH is a strong base and HCl is a strong acid, it can be deduced that either methyl or phenolphthalein (pH indicators) can be used as the indicator The titrant, in this case HCl, is a solution of known concentration, in other words a standard solution, that is added (titrated) to another solution to determine the concentration of solution of unknown concentration, the analyte (NaOH(aq)) Procedure: The equipment was rinsed with the appropriate solutions. 25cm3 of sodium hydroxide solution was measured with a pipette and placed in a conical flask. The burettete was filled to the zero mark with the standard 0.1mol dm-3 HCl ensuring that no air bubbles were in the tip. Two (2) drops of methyl orange indicator was added to the conical flask and swirled. The conical flask was titrated with constant swirling against the acid until one drop of acid turns the mixture orange with a tinge of pink. Steps 2 and 3 were repeated until three concordant values were obtained. Results were placed into a suitable table showing the readings of the burettete and the number of titrations. Results and Calculations
CALCULATIONS: 1. Determine the average volume of acid used in the titration and the number of moles of HCl used. Average=22.2+23.3 +23.0/3= 22.8 Moles hcl(aq) + NaOH(aq)→H2O +Nacl(aq salt) molar concentration=0.1moldm ̄3 v =25cm3 n=c*v/1000 =0.0025 1:1 =0.0025mol C=n/v*1000 c= 0.0025*1000/47.33 =0.05moldm ̄3 mass concentration= molar conc* molar mass NaOh=23+16+1=40 g*0.01moldm ̄3 =2gdm ̄3 3. If the NaOH was prepared approximately a week ago and its mass concentration was 8gdm 3what is the percentage purity of the NaOH at present? purity = mass of the pure substance in the sample/mass of the sample*100 8gdm ̄3/40*100 =20% 4. The equivalent point is point at which the added titrant is chemically equivalent to the analyte. 5. The endpoint of this reaction could have been determined using changes in pH. Sketch a pH curve for this experiment and show on the graph, the equivalence point. It is always stressed that the burette should always be to TWO decimal places and not ONE. Suggest a reason for this emphasis. The burette should always be recorded in two decimal places because the second decimal place is an estimate for more accuracy of the results. Reading at one decimal place gives a percentage error at each reading. Discussion: A titration experiment is used to determine the unknown concentration of an Identified analyte substance of interest .In this type of experiment a reagent (titrant) is Prepared as a standard solution, then a known concentration and volume of the prepared Titrant reacts with analyte to determine the concentration. An analyte is the substance that is being analyzed, while titrant is a Solution of reagent that reacts with the analyte. The endpoint is the point during a titration When an indicator shows the amount of reactant necessary for reaction. It is the point where the symbol changes color. On the other hand, point of equivalence in titration refers to the point at which the added titrant is chemically equivalent to the sample. Analyte is the closeness of a result to an accepted value and precision is the closeness of the measurements themselves which relates to the burette readings being recorded for more precise readings. Source of Error: end point error, indicators which change color to indicate when the reaction has stopped, do not change instantly. In this case of acid base titration, the indicator may first Lighten in color before changing completely. Precaution: 1. Clean all spills
Conclusion: The concentration of NaOH was obtained by an accurately known solution of HCL Download 187.37 Kb. Share with your friends:
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