Post on 28-Oct-2014
Embed Size (px)
UNIVERSITI TEKNOLOGI MARA FAKULTI KEJURUTERAAN KIMIA ENGINEERING CHEMISTRY LABORATORY (CHE485) NAME STUDENT NO. GROUP EXPERIMENT DATE PERFORMED SEMESTER PROGRAMME / CODE SUBMIT TO No. 1 2 3 4 5 6 7 8 9 10 11 12 Title Abstract/Summary Introduction Aims Theory Apparatus Methodology/Procedure Results Calculations Discussion Conclusion Recommendations Reference / Appendix TOTAL MARKS : NUR NAJWA BINTI YUNUS : 2011207298 : EH 222 1A : CONCENTRATION OF ACETIC ACID : 26TH SEPTEMBER 2011 :1 : BACHELOR OF ENGINEERING IN CHEMICAL AND BIOPROCESS : CIK NURUL ASYIKIN MD ZAKI Allocated Marks (%) 5 10 5 10 5 10 10 10 20 5 5 5 100 Marks
Remarks: Checked by :
TABLE OF CONTENTS
Abstract. Introduction.. Aims.. Theory... Methodology. Results... Calculations... Discussion. Conclusion. Recommendations. References.. Appendices.
1 2 3 4 5 8 15 17 19 20 21 22
Vinegar is a dilute solution of acetic acid and popular for its domestic use. This experiment was conducted in order to determine the percent by mass of acetic acid in vinegar by titration with a standardized sodium hydroxide solution. The process that plays major role in this experiment was titration whereby the required acid was titrated with sodium hydroxide (NaOH). In this experiment, there were two acids used which were potassium hydrogen phthalate (KHP) as a
primary standard acid and vinegar itself. Both of the solutions were titrated until a sudden change of the pH is noted. The sudden change was referred as the equivalence point. This point indicated the amount of NaOH required to neutralize the acids. The results of both experiment was used to calculate the mass of acetic acid in the vinegar. The average percent of mass of acetic acid is 5.0146 %. Therefore, the experiment was completely and successfully done.
The term of concentration is used by scientist to estimate the amount of solute dissolved in a given quantity of solvent or quantity of solution. The greater the amount of solute dissolved in a particular amount of solvent, the more concentrated the resulting solution. Two specific terms are used to express the concentration, which are molarity and percent by percent by mass. Stoichiometry with the relative quantities of reactants and products in chemical
reactions. After balancing the chemical equation, the relations between quantites of reactants and products form a ratio of whole numbers. Stoichiometry wil be used to calculate quantities such as mass, number of moles, volume and percent yield. Stoichiometry is related to the law of conservation of mass and with a few calculations, we can predict how elements and components diluted in a standard solution react in certain experimental conditions and thus, able to determine the molarity. Molarity (M) expresses the concentration of a solution as the number of moles of solute in a liter of a solution. Therefore, the formula is as below: ( ) whereby percent by mass is the mass in grams of solute per 100 grams of solution and the formula is as below:
Acetic acid, CH3COOH is the main component of vinegar other than water. Typically, vinegar consist of 4 to 18% of acetic acid by mass. Vinegar is always used for medical purposes, culinary and agricultural purposes. Therefore, some country strictly limited the percent of acetic acid inside commercial vinegar for safety. Though acetic acid is considered as weak acid, higher concentration of acetic acid may results to the permanent eye damage, skin burns and irritation to mucous membrane. Titration is a common laboratory method to determine the unknown concentration of an identified analyte. Titration method is the process involved in neutralization of acid-base. The base is added to acid until sudden change of the pH of the solution. The changes of the pH is very sudden. Therefore, by using titration method, the volume of base poured into the acid can be controlled and by small increments. Through this method, the equivalence point in which the solutions are neutralize can be determined. 2
The objective of this experiment is to: apply the process of titration determine the molarity of a solution determine the percent by mass of acetic acid in vinegar by titration with a standardized sodium hydroxide solution.
In this experiment, titration is the major process involved to get the most accurate result. In the titration process, a burette is used to dispense solution in a small amount. Most of the burette has the smallest calibration unit of 0.1mL.
Figure 1: a) Shows a 50-mL burette. b) Smallest calibration unit, 0.1-mL
While conducting this experiment, the equivalence point will occurs when the moles of acid in the solution equals the moles of base added in the titration. For example, amount of 1 mole of sodium hydroxide (NaOH), is necessary to neutralize 1 mole of acetic acid (CH3CO2H), as shown below: NaOH(aq) + CH3CO2H(aq) NaCH3CO2(aq) + H2O(l) [Eq. 3] The titration has reached the equivalence point if there is a sudden change of pH in the solution . pH is the negative logarithm in base 10 of [H+] and related to the hydrogen ion concentration. pH = -log10[H+] pH scale varies according to the basicity and acidity of a solution. The pH of a neutral solution is 7.00 at 25C. If the pH is below 7.00 the solution is considered as an acid whereas if it is above 7.00, it is referred as a basic solution. The pH of a solution can be measured quickly and accurately with a pH meter. The electrode of the pH meter was inserted into a beaker with required acid while the solution was titrated with NaOH solution. The hydrogen ions will be neutralized as NaOH is incrementally added to the acid solution in which resulting to the increased of the pH of that particular acid. After a sufficient amount of NaOH is added, the next drop of NaOH will cause a sudden sharp increase in pH. The equivalence point of titration indicates the volume of based required to completely neutralized the acid.
Figure 2 Titration curve of weak acid titrated with NaOH
During this experiment was conducted, titration of a vinegar sample with a standardized NaOH solution will be performed. In order to standardize the NaOH solution, a primary standard acid solution is initially prepared. Potassium hydrogen phthalate (KHC8H4O4) and oxalic acid (COOH)2 were commonly used as a primary standard acid while sodium carbonate, Na2CO3, is the commonly used base. Potassium hydrogen phthalate (KHP) was used throughout this experiment as a primary standard acid. The KHP was produced by dissolving around 1.500g with 30 mL of distilled water. In order to choose the standard acid or even bases,they must have at least these characteristics: available in at least 99.9 purity have high molar mass stable upon heating must be soluble in the required solvent The reaction equation of this reaction between KHP and NaOH solution is shown below: KHC8H4O4(aq) + NaOH(aq) KNaC8H4O4(aq) + H2O(l) [Eq. 4] After the NaOH solution was standardized, the process of titration with 10.0 mL aliquots of vinegar began. The equation of the reaction is: CH3COOH(aq) + NaOH(aq) NaCH3COO(aq) + H2O(l) [Eq. 5] By referring to the equation above, the molarity and the percent by mass of acetic acid can be determined.
Material and Apparatus Solid NaOH Distilled water KHP Beakers Measuring cylinder Magnetic stirrer pH meter Vinegar 10 mL volumetric pipette Analytical Balance
Prodecure Experiment A Standardization of Sodium Hydroxide Solution 1. 250 mL of approximately 0.6 M sodium hydroxide solution was prepared from NaOH solid. The solution was prepared in a beaker after the calculation was checked with the laboratory instructor. The calculation was recorded. 2. The beaker was placed and tarred on the balance. 1.5 grams of KHP was added to the beaker. The mass of the KHP was recorded to the nearest 0.001 g. 30 mL of distilled water was added. The solution was stirred with magnetic stirrer until the KHP has dissolved completely. 3. The solution was titrated with NaOH and the pH was recorded with 1 mL additions of NaOH solution. 4. Steps 1 to 3 were repeated and two more solutions for NaOH standardization were prepared. 5. The graph of pH versus NaOH was plotted. The volume of NaOH required to neutralize the KHP solution in each titration were determined from the plots 6. The molarity of sodium hydroxide for titrations 1, 2 and 3 was calculated. 7. The average molarity of sodium hydroxide solution was calculated. The resulting sodium hydroxide concentration was used in part B of the experiment. 6
Experiment B Molarity of acetic acid and mass percent in vinegar 1. 10.00 mL of vinegar was transferred to a clean, dry 250 mL beaker using a 10 mL volumetric pipette. 90.0 mL of water was added in order to cover the pH electrode tip during the titration. 2. 1.0 mL of NaOH was added to the vinegar solution and the pH was recorded. 3. The above steps was repeated twice more. 4. The graph of pH vs NaOH was plotted and from the plots, the volume of NaOH required to neutralize the vinegar in each titration. The data was recorded. 5. The molarity of acetic acid was calculated for titrations 1, 2 and 3. 6. The average molarity of acetic acid for each titration was calculated. 7. The percent by mass of acetic acid in vinegar was calculated for titrations 1, 2 and 3. 8. The percent by mass of acetic acid in vinegar was calculated.
KHP Titrated With NaOH14.00
8.00 pH 6.00 4.00 2.00 0.00 0.00 5.00 10.0012.50
Volume of NaOH (mL)
Graph 1 - Titration 1
KHP Titrated With NaOH14.00