Acid base and redox titration of vitamin C - Lab Report Example

Lab Partner: Lab Meeting Time: Acid base and redox titration of vitamin C Introduction:This report seeks to determine the amount of vitamin C in a tablet. Using both redox reaction between vitamin C extract and iodine solution, and vitamin C extract and sodium hydroxide solution, the experiment will carry out titration reactions and apply stoichiometry concepts to determine the percentage of vitamin C in a tablet. The experiment will apply the concept of molality and stoichiometry to determine the number of moles and mass of vitamin C. Molarity is the concentration of solute particles in a solution. Measured in moles per unit volume, it shows the concentration in terms of the reacting units rather that mass, a property that facilitates stoichiometry. Stoichiometry on the other hand defines the ratio of reacting chemicals. Procedure: Acid base reaction The mass of a vitamin C tablet was measured and recorded before the tablet was ground into powder. The powder was then transferred into a 125 ml Erlenmeyer flak and 50 ml of water added. The mixture was then filtered into a 250 ml flask and the residue re-extracted using 50 ml of water. With addition of 3 drops of phenolphthalein indicator to the solution and a piece of paper placed bellow the flask, the filtrate was titrated with standardized sodium hydroxide till the first drop at which the titrant turned pink. Redox reaction The procedure for extracting vitamin C was repeated followed by a titration with iodine solution. An indicator was however not used. Data/results: The equations for the experiments are shown bellow, Equation for the acid base reaction C6H8O6(aq) + NaOH(aq) -> H2O(l) + Na+(aq) + C6H7O6-(aq) Equation for the redox reaction C6H8O6(aq) + I3-(aq) -> 3 I-(aq) +C6H6O6(aq) + 2H+(aq) Table 1 and table 2 below summarize the results of the acid base reaction. The mole ration is derived from the equation of the reaction between vitamin C and sodium hydroxide solution shown bellow Table 1:The table below summarizes the results of the acid base reaction Data Trial Mass tablet used 0.66 g Molarity of NaOH (moles/L) 0.1996mol/L Initial volume of NaOH (mL) 1.9 mL Final volume of NaOH (mL) 17.9 mL Volume of NaOH used 16ml Moles of NaOH used 0.0031936mol Vitamin C: base molar ratio 1:1 Moles of vitamin C 0.0031938mol Mass of vitamin C 0.564g Percent of vitamin C in the tablet 85.5% Table 2:The table below summarizes the results if the redox reaction experiment Data Trial Mass tablet used 0.67g Molarity of I3- (moles/L) 0.0990mol/l Initial volume of I3- (mL) 4.1 mL Final volume of I3- (mL) 28.6 mL Volume of I3- used 24.5 ml Moles of I3- used 0.0024mol Vitamin C: base molar ratio 1:1 Moles of vitamin C 0.0024mol Mass of vitamin C 0.43 g Percent of vitamin C in the tablet 64.18 % The equations used to find the answers in the trials are written bellow, Equation for table 1 C6H8O6(aq) + NaOH(aq) -> H2O(l) + Na+(aq) + C6H7O6-(aq) Equation for table 2 C6H8O6(aq) + I3-(aq) -> 3 I-(aq) +C6H6O6(aq) + 2H+(aq) Discussion/Conclusion:Chemical properties of substances initiate reactions. The reduction property of vitamin C, for example, is responsible for the chemical’s property to initiate reactions with other chemicals. The acid has a high tendency to donate electrons to other chemicals forming a basis for reactions. Based on stoichiometry and known information of a chemical in reaction with vitamin C, elements such as the number of moles and even mass of vitamin C can be determined from a reaction that can be either an acid base reaction or a redox reaction. The acid base reaction involved sodium hydroxide solution, the base in the reaction, and vitamin C, the acid. The equation for the reaction is given as follows C6H8O6(aq) + NaOH(aq) -> H2O(l) + Na+(aq) + C6H7O6-(aq) Vitamin C was oxidized in the process while sodium hydroxide was reduced. The redox reaction is on the other hand represented by the following equation, C6H8O6(aq) + I3-(aq) -> 3 I-(aq) +C6H6O6(aq) + 2H+(aq) The oxidation reaction is given by the following equation C6H8O6(aq)->C6H6O6(aq)+ 2H+(aq) The reduction equation is given by I3-(aq) -> 3 I-(aq) From the chemical equation, vitamin C is oxidized while iodine ions are reduced. The accurate titration is the acid base reaction. This is because it offers the same percentage composition as indicated on the vitamin C tablet used. The experiments offered different results. While the redox reaction yielded a percentage composition of 64.19 percent, the acid base reaction yielded 85.5 percent. The difference in the numbers could be due to a number of errors. The first type of error that could have led to the difference is inaccurate measurement of the reactants. Such could occur in measuring readings in the titration process for the redox reactions. Errors could have similarly occurred in failure to identify the exact point of neutralization in the experiment. Another type of error that could have led to the difference in the percentage composition of vitamin C in the tablet is possible physical loss of components of the tablet during crushing. The powder could have been blown away. Similarly, there is possibility of incomplete dissolution in the extraction process or incomplete reaction if the neutralization point was predetermined before completion. The extraction process was necessary to separate vitamin C from other components of the tablet. This further eliminated other possible reactants that could have interfered with the stoichiometry of the reactions. An indicator serves the purpose of identifying the point of neutralization in a reaction. It was therefore used to indicate the point at which all the vitamin C reacted. The indicator was not used in the redox reaction because the color of iodine serves the same purpose as it changes upon neutrality. The kind of error introduced by extracting the vitamin C is systematic error. This is because extraction was part of the design and procedure of the experiment. Effects of using hydrochloric acid instead of water, in the extraction process Application of hydrochloric acid instead of water would catalyze the titration reactions because of the stronger ionization effect of hydrochloric acid as compared to water. Conclusion: The report, using stoichiometry, determined experimentally that the percentage composition of ascorbic acid in a vitamin C tablet is 85.5 percent as indicated on the tablet. Though the results of the two experiments differed, the correspondence between the acid base reaction results and the prescribed composition indicates accuracy. The two experiments however yielded different results that are attributable to experimental errors. The reaction in the two experiments were based on the following equations, C6H8O6(aq) + NaOH(aq) -> H2O(l) + Na+(aq) + C6H7O6-(aq), C6H8O6(aq) + I3-(aq) -> 3 I-(aq) +C6H6O6(aq) + 2H+(aq) Calculations:Volume of sodium hydroxide used= 17.9 - 1.9 = 16ml Number of moles of NaOH used =molarity*volume =0.1996*0.016 =0.0031936 moles Moles of vitamin C =0.0031936 Mass of vitamin C= number of moles*molar mass =0.0031936*176.7 =0.564 g =85.5% Calculations for redox reaction Volume of iodine solution used= 28.6-4.1= 24.5 ml Number of moles of NaOH used =molarity*volume =0.0990*0.0245 =0.0024 moles Moles of vitamin C =0.0024 Mass of vitamin C= number of moles*molar mass =0.0024*176.7 =0.43 g = 64.18 Read More