To standardize an unknown solution of hydrochloric acid Method: See INSTRUCTIONS for practical 6. 2 & 6. 3 Results: Attempt No. | Titre (mL)| | 1| 20. 9| Rough Titration| 2| 20. 5| | 3| 20. 7| Concordant Titres| 4| 20. 7| | 5| 20. 7| | (1) Tabled Results (2) Concordant Titrations Results 20. 7 mL| 20. 7 mL| 20. 7 mL| Average of Concordant: (20. 7 + 20. 7 +20. 7) 3= 20. 7 mL Calculations: (1) Equations a) Titration of HCl with Sodium Carbonate: Na2CO3 + 2HCl 2NaCl + H2O + CO2 (2) Concentration of Sodium Carbonate (Na2CO3)
Molar mass of Na2CO3: 22. 99*2+12. 01+16*3=105. 99 Mass of Na2CO3: 1. 3 g Number of moles : n=mM =1. 3 105. 99=0. 012265308 mol Volume Na2CO3 solution: 250 mL : 0. 250 L Concentration: Concentration of Sodium Carbonate is 0. 049 mol L-1 c=nV = 0. 012265308 0. 250=0. 049061232 mol L-1 (3)Concentration of HCl Volume of Na2CO3 solution: 20 mL : 0. 020 L Number of moles of Na2CO3: n=C x V =0. 049 x 0. 020 =0. 00098 mol Volume of HCl: 20. 7 mL (average of concordant result based on titration) : 0. 0207 L Number of moles of HCl: Stoichiometric Ratio between Na2CO3 and HCl: 21 (From equation above) nHCl =2 x nNa2CO3 =2 x 0. 00098=0. 0196 mol Concentration: Concentration of Hydrochloric Acid is 0. 095 mol L-1 CHCl=nHClV = 0. 00196 0. 0207 =0. 0946859903 mol L-1 Analysis & Evaluation: (1) Conclusion The concentration of the Hydrochloric acid is known to be 0. 10 mol L-1 (2) Random Errors Random errors are chance variations between successive measurements over which the experimenter has little or no control. They are linked to the precision of the measurements. Possible random errors that occur during the experiment may include: * Misreading the bottom line of the meniscus (i. e. not eye-level), causing the measurement to be slightly off its actual volume.
This leads to imprecision of the overall result of the experiment. * Incorrect judgment of the end point colour change. Resulting in excess volume of hydrochloric acid, thus leading to the miscalculation of the concentration. * Air bubbles occurring when transferring the sodium carbonate with the pipette, making the actual volume less than the desired amount (20 mL). (3) Systematic Errors Systematic errors are recurrent errors inherent in the apparatus or experimental method. They are linked to the accuracy of measurements. Some possible systematic errors that may occur throughout the experiment are: A measuring instrument is not calibrated or is incorrectly calibrated. Resulting the reading and the actual amount to be off throughout the experiment. The measured value can either all be too high or too low. * Contamination of the sodium carbonate as a substance use for the standard solution. Impurity of the substance means that there are other undesired substances included in the solution, making the actual concentration of sodium carbonate to be less. * Electronic scale was not ‘zeroed’ after placing the watch glass, making the magnitude of the weighed amount to be more than the actual. (4)Evaluation Questions: