Acid base titration - Lab Report Example

? Acid base titration Aim The experiment intended to ascertain concentrations of Dilute Hydrochloric acid and Dilute Sulphuric Acid solutions by conducting Acid-Base titrations. Hypothesis Phenolphthalein change of color from pink/purple to colorless signified a transformation of the solution’s nature from being basic to acidic, which was the reaction’s endpoint or neutrality point. This is because in acidic, basic conditions phenolphthalein indicator usually indicates colorless and pink/purple colors respectively. Background theory Acid – base titration is one of the most essential Titrimetric analysis techniques commonly used in wet analysis to determine quantities or concentrations of the reacting reagents (Patnaik, 2010, p. 57). This is a neutralization reaction whereby its endpoint or neutrality point is marked by the change of phenolphthalein’s color from pink/purple to colorless. Colorless color in this experiment is an indication the reaction has reached its endpoint or undergone a complete neutralization route, hence basic condition is exhausted and instead acidity is increasing. Endpoint refers to a point where an indicator changes its color and assumes another thereby implying an acid has completely neutralized the available basic solution (Parsons, Forsythe, Edge & Bewick 793). At exact endpoint, the solution’s nature is neutral bearing a pH value of 7 similar to that of pure water. The addition of more acid solution reduces the solution’s pH from 7 towards 1, hence increasing its acidity nature compared to when it was a basic and a having a pH value more than 7. However, the color continues to remain the same but extent of acidity increases with addition of extra acid solution to the titrant, which in this experiment is a Standard 0.10 mol. /dm3 Sodium Hydroxide. Suppose there is a need to plot titration curves, then potentiometer is more accurate than either weak organic acid indicator or a weak organic base indicator (Patnaik, 2010). Since, it gives exact values compared to the latter two, which only relays the change of solution’s color (Patnaik, 2010.p. 61). An indicator is a weak organic acid or weak organic base having a formula of HY or HOY correspondingly, where Y represents a complex organic ion (Patnaik, 2010). During reaction, HOY or HY indicator usually dissociates as shown in the reversible equation below (Patnaik, 2010, p. 61). HY + H2O H3O+ + Y- Color -1 Color – 2. Reversibility in the above equation depends on the amount of either acid or basic solution added during neutralization process, which implies more base or acid shifts the process to the right (Patnaik, 2010). Hence, change of color from 1 to 2. The general equation involved in the neutralization process is, Acid + Base/Alkali Salt + water (Neutralization reaction equation) Essential components or agents for the above neutralization process to reach its completion state include hydronium ions, H3O+ (aq) from the acid and hydroxide ions, HO- (aq) from a base/alkali. However, these ions must be in aqueous form (in water) to facilitate their free movement besides ensuring intimate interactions when reacting. Respective equations for both Dilute Hydrochloric acid and Dilute Sulphuric Acid are, Ordinary equations (1) HCl(aq) + NaOH(aq) ® NaCl(aq) + H2O(l) H+(aq) + Cl-(aq) +Na+ + OH(aq) ® Na+ + Cl-(aq) + H2O(l) (2) H2SO4 (aq) + NaOH(aq) ® NaSO4(aq) + H2O(l) 2H+(aq) + SO4- (aq) + Na+(aq) + OH-(aq) ® Na-(aq) + SO4-(aq) + H2O(l) After eliminating spectator ions these equations reduce to, (1b) H+ (aq) + OH (aq) ® H2O (l) (2b) 2H+ (aq) + OH-(aq) ® H2O (l) Or (3) H3O+1 + OH- ® 2H2O (l) However, moles of H+ ions in each side of the equation should be equal for the reaction to proceed to the right or neutralization to occur (York, 175). Molarity concept Titration calculation in this experiment entails use of stoichiometric mole ratio of H+ and OH- ions (Parsons, Forsythe, Edge & Bewick). Moles’ ratio comparison in this experiment will be at the endpoint. This is because endpoint usually signifies complete reaction or neutralization process where the pH = 7 similar to that of pure water. MaVa = MbVb Where Ma = Molarity of acid Va = Volume of acid Mb = Molarity of base Vb = Volume of acid Apparatus and reagents Burette Pipette filler Clamp and stand Filter funnel Small beaker Large beaker Three conical flasks White paper Safety glasses and lab coats Standard 0.10 mol./dm3 Sodium Hydroxide (NaOH) Dilute Hydrochloric acid of unknown molarity Dilute Sulphuric acid of unknown molarity Phenolphthalein indicator Method After putting on safety equipment, an approximate 75 cm3 0.1 M standard alkali (NaOH) was placed in a small beaker whereas 100 cm3 in a large beaker. The burette was then clamped firmly and filled with acid right above the zero mark using a filter funnel. The beaker was placed below the burette and the tap turned on to ensure the jet is filled with dilute hydrochloric acid. Then the meniscus line was aligned properly with the zero mark such that the curved surface of the acid was lying on the zero line. With the aid of a pipette, 25cm3 of the standard basic solution was drawn from the beaker and emptied into a conical flask. The solution was allowed to drip into the flask until the bottom of the meniscus aligned well with the lowest pipette’s calibrated mark. There was an addition of three to four drops of the phenolphthalein indicator to ensure the color was deep red or purple. In order to ensure effective monitoring of color change throughout the neutralization process, white paper was placed under the conical. Then burette was turned to allow Dilute Hydrochloric acid to run into the conical flask rapidly until the solution changed color from red to colorless. This was the first rough estimate that was tabulated but not meant for calculation. After the first rough trial, the pipette, burette was refilled again with 25cm3 of the standard basic solution and Dilute Hydrochloric acid respectively. The 25cm3 of the standard basic solution in the pipette was drained into a second conical flask. This was followed by the addition of acid rapidly until it the amount reached within the 2 cm3 of the initial rough reading, then followed by careful titration until the color of the indicator disappeared completely. The value obtained from the second trial was tabulated as an accurate reading meant for calculation. The entire titration procedure was repeated until there were other two accurate readings whose range difference was within 0.1 cm3. Finally, the second phase encompassed repeating titration procedure with Dilute Sulphuric Acid coupled with ensuring effective recording of all resulting volumes in different tables. The culmination of this experiment after obtaining the required results and tabulating them correctly was to rinse all the glassware and placing them in the washbowls. Fig1: PrenHall. n.d. 4.6 Solution Stoichiometry and Chemical Analysis. [electronic Image] Available at: [Accessed 10Th December 2013]. Results Table 1: With Dilute Hydrochloric Acid Titration Volume of NaOH/cm3 Initial volume of Acid/cm3 Final volume of Acid/cm3 Titre/cm3 First rough result 25 0 8.95 8.95 Second 25 8.95 17.95 9.00 Third 25 17.95 26.80 8.85 Fourth 25 26.80 35.90 9.10 Average 25 - - 8.98 Table 2: With Dilute Sulfuric Acid Titration Titration Volume of NaOH/cm3 Initial volume of Acid/cm3 Final volume of Acid/cm3 Titre/cm3 First rough result 25 0 10.80 10.80 Second 25 10.80 21.75 10.95 Third 25 21.75 32.60 10.85 Fourth 25 32.60 43.85 11.25 Average 25 - - 11.01 Calculations Calculating the molarity of Dil. HCl: HCl(aq) + NaOH(aq) ® NaCl(aq) + H2O(l) 1) nNaOH = MNaOH x VolNaOH = 0.10 x (25cm3 /1000) = 0.10 x 0.025 dm3 nNaOH = 2.5x10-3 moles 2) Checking the more ratios in equation (1), one mole of Dil. HCL reacts with one mole of NaOH. This implies at endpoint one mole of Dil. HCL requires a similar number of moles of NaOH for complete neutralization. Hence, based on (1) 1 moleHCl = 1 moleNaOH Therefore, nHCl = 2.5x10-3 moles 3) MHCL = Moles/Volume (mean Titre) VHCL = 8.98 cm3 = 8.98 x 10-3 dm3 MHCL = 2.5x10-3 moles /8.98 x 10-3 dm3 = 0.27839 mol.dm3 The concentration for Dilute Hydrochloric acid is 0.27839 mol.dm3. Calculating the molarity of NaOH: H2SO4 (aq) + NaOH(aq) ® NaSO4(aq) + H2O(l) From the previous calculation, moles for NaOH is, 1) nNaOH = 2.5x10-3 moles 2) Deducing from the above equation, I mole of Dil. H2SO4 reacts with 2 moles of NaOH. From moles ratio at endpoint this implies 1mole of Dil. H2SO4 = 2 moles of NaOH 2.5x10-3 /2 = 2.5x10-3 (Equating moles) 1.25x10-3 moles of Dil. H2SO4 = 0.025 moles of NaOH 3) MH2SO4 = moles/volume (mean titre) VH2SO4 = 11.01 cm3 = 11.01 x 10-3 dm3 = 1.25x10-3 mol/ 11.01 x 10-3 dm3 = 0.1135 mol.dm3 The concentration for Dil. Sulphuric acid 0.1135 mol.dm3. Percentage error Percentage Error Burette =  x100 = (0.05/ 8.98 cm3)*100 = 0.005568% = 0.005568% Percentage Error Pipette =  x100 = (0.05/25 cm3)*100 = 0.002% The Total Percentage Error experiment = Percentage Error burette + Percentage Error pipette = 0.005568% + 0.002% = 0.007568% Discussion The aim of this experiment was to ascertain concentrations of unknown Dilute Sulphuric Acid and Dilute Hydrochloric acid solutions. This by titrating them against a standard 0.01M sodium Hydroxide solution and then calculating their respective molarities after tabulating results in tables. Observing the endpoint of each experiment’s trial was through colour change from red/pink to colourless solution and recording their titre volumes. This was through addition of three to four drops of phenolphthalein indicator in the conical flask solution containing standard 0.01M sodium Hydroxide solution. Before the commencement of titration process, the colour of the indicator was purple/red in the basic solution then changed into colourless during gradual addition of acidic solutions (Dil. HCL and Dil. H2SO4) as shown in Fig 1. In this experiment, percentage error was 0.007568%, which signifies high accuracy based error comparison scale because it is below 2%. According to the scale, percentage error that is between 2% to 5% signifies experimental results are reasonably accurate while that is over 5% relatively inaccurate. During titration, sudden change of colour from pink/purple to colourless signified complete neutralization process at endpoint whereby hydrogen ions (H+) in the acidic solution are equal to hydroxide ions (OH-) from the base. Therefore, this implies the number of moles for Dil Acidic solutions at endpoint is equal to those of the titrant solution (NaOH), which is the basic concept used in calculating acids’ respective molarities. In calculating average titre volumes, there was no inclusion of the first trial volumes for each type of acid because they were only rough estimates. However, more emphasis was from the second trials because they were more accurate than the first ones. After computing mean values, titres volumes for Dil. HCL, Dil. H2SO4 were 8.98 cm3 and 11.01 cm3 respectively. Difference in volumes between these two acids was due to their respective volumes whereby Dil. HCL is a monoprotic acid, whereas Dil. H2SO4 diprotic acid. Based on equations (1) and (2) above, complete neutralization of 1 mole of NaOH requires 1 mole of HCL acid, whereas in the case of H2SO4 acid it required 2 moles of the base. Dissociations of these two acids in solutions are as per the following equations (4) and (5), (4) HCl ? H+ + Cl- (5) H2SO4 ? 2H+ + SO4- General neutralization equation used in this experiment, which encompassed base and acids was, Acid aq + base aq > salt aq + water L Titration equations H2SO4 aq + NaOH aq? Na2SO4 aq + H2O l HCl aq+ NaOH aq? NaCl aq+ H2O l Strengths and weakness The use of titration method in determining concentrations of unknown solutions is very effective, simple and fast. The experimenter only needs to be keen while observing colour change during titration to come with accurate values that will help him or her during calculations. Through this method, there are almost minimal errors and deviations from the exact value as indicated by percentage error, which is 0.007568%. This is because before commencement of determining respective volumes of acids whose molarities were unknown, basic solution was used to rinse all remnant acids that could have led to erratic values. In addition, determining endpoint using this experiment is very effective, which entails only observing colour change from pink/purple to colourless. Hence, manage to obtain exact volumes of acid meant to bring a certain amount base to a complete neutrality point. Major weakness associated with this experiment that can lead to inaccurate calculation of the required concentrations is the experimenters’ inability to take the readings correctly. This is especially evident when a person instead of reading at the bottom of the meniscus erroneously ends up taking readings from the top. This mode of reading despite producing small differences compared to the exact readings eventually yields to major errors having big margins. To avoid occurrence of errors caused by improper reading, the experimenter should always take calibrated readings that aligns exactly with the bottom of the meniscus. Other possible sources of errors include contaminated titration apparatus and reagents whereby a person may assume they are clean for use. Therefore, the experimenter ought to ensure the availed apparatus are clean and moisture free to avoid any reagents’ contamination, which in many times lead to side reactions and unnecessary dilutions. Dilution or moisture usually tends to deviating volumes due to increasing water content in the reagents, which alters their concentrations. In addition, the experimenter may fail to fill the burette such that he or she has cleared all bubbles in it. Health and safety Exposure Safety measure 1 Breakage of glassware, for instance, burettes, beaker, pipette when handling them or hit each other and results to cuts. Handling them with care, placing them in their correct racks and wearing gloves if possible. In case there are breakages that have occurred, it is advisable to use dustpan to collect broken pieces. 2 Dilute acids (HCL & H2SO4) posses a burning effect on human skin. Being extra careful in inspecting any spilled traces of acids on the working bench or apparatus. The experimenter can also wear hand gloves. 3 NaOH and H2SO4 are known to cause eye irritation and skins burns due to their corrosive nature especially if they are in Diluted form The prevention of this is by wearing protective clothing like lab coats and eyes’ protecting devices (safety glasses) when doing experiment. 4 NaOH is corrosive to the skin and causes burning effect Desist from blowing the pipette when drawing out the remnant drops but instead touch the flask with its tip. Conclusion This experiment’s core purpose entailed to determine unknown concentrations of Dil. Hydrochloric acid Dilute Sulphuric acid by use of titration method. Titrant used in this experiment was standardized 0.10M sodium hydroxide where after calculation molarities for Dil. HCL, Dil. H2SO4 were were 8.98 cm3 and 11.01 cm3 respectively. In this experiment, the percentage error compared to the scale was highly accurate, which was 0.007568%. Titration is an essential method having variety of applications in industrial field in terms of reagents’ analysis. This is evident in pharmacological firms where specialists normally use it for quality control to ascertain exact quantities needed to mix varied emollients meant to prepare a certain drug (Ghosal & Srivastava, 2009). Mainly, this enables those formulating a certain drug come up with an exact product possessing required characteristics that will align with what the company will states while marketing it. In wine industry, titration acts an appropriate approach commonly preferred to regulate the acidity of a given brand such that its content will not have any detrimental effect to all people consuming it. This is especially among those who have advanced in age whereby due to their health condition the consumed alcohol will not have any detrimental effects on them. Determining of acidity in wine sector also extend in food industry where processors are capable of ascertaining what quantity to include in a certain product that will not be harmful to human health or temper with inherent nutrients. References Ghosal, S., & Srivastava, A. K. 2009. Fundamentals of bioanalytical techniques and instrumentation. New Delhi, PHI Learning. n.d. Neutralization Reactions. [Online] The University of Mephis. Available at: [Accessed 10Th October 2009]. Parsons, Richard., Forsythe, Therese., Edge, Jonathan & Bewick, Sharon. 2010. CK-12 Chemistry, Volume 1. Palo Alto, California: CK-12 Foundation. Patnaik, Pradyot. 2010. Handbook of Environmental Analysis: Chemical Pollutants in Air, Water, Soil, and Solid Wastes, Second Edition. Boca Raton, Florida: CRC Press. PrenHall. n.d. 4.6 Solution Stoichiometry and Chemical Analysis. [Electronic Image] Available at: [Accessed 10Th December 2013]. York, Deanna. 2010. More Teacher Friendly Chemistry Labs and Activities. Bloomington, IN: Authorhouse. Read More