Titration with Oxalic Acid

Titration is a versatile analytical procedure that can be used for a wide variety ofchemical analyses. For example, when your town’s water supply is tested for purity,or pond water is tested for dissolved oxygen and contaminants, chances are atitration is carried out. Some tests essential for a medical diagnosis require atitration of various body fluids.A titration makes use of a known reaction between two chemicals. A solutionof unknown concentration is reacted with a precisely measured amount of anotherchemical. An appropriate indicator must be used to determine when chemicallyequivalent amounts of each chemical are combined, that is, when no excess ofeither...
Nội dung trích xuất từ tài liệu:
Titration with Oxalic Acid TitrationwithOxalicAcidIntroduction Titration is a versatile analytical procedure that can be used for a wide variety of chemical analyses. For example, when your town’s water supply is tested for purity, or pond water is tested for dissolved oxygen and contaminants, chances are a titration is carried out. Some tests essential for a medical diagnosis require a titration of various body fluids. A titration makes use of a known reaction between two chemicals. A solution of unknown concentration is reacted with a precisely measured amount of another chemical. An appropriate indicator must be used to determine when chemically equivalent amounts of each chemical are combined, that is, when no excess of either reactant is present. This is known as the equivalence point. To measure solution volumes accurately, finely calibrated pipets and burets are used. Titrations are commonly used to determine the strength of acids or bases. Acid-base titrations follow a relatively standard procedure for analysis of acid or base strength. The concentration of either an acid or a base solution can be determined. A measured amount of acid is neutralized by reaction with a base solution titrated from a buret. Consider the following example: HCl + NaOH → NaCl + H2O (Known) (Unknown) The example shows that the reaction is a double replacement in which the products are a corresponding salt and water. For reactions of strong acids and bases, the equivalence point pH is 7, but for weak acids it is somewhat higher. If a graph is made of pH vs. volume of base added, the equivalence point is always halfway along the S curve as labeled in the illustration. Note that there is a large pH change around the equivalence point with very small additions of base. In this investigation, you will determine the concentration of a basic solution by titration with oxalic acid, H2C2O4, a moderately weak acid with and equivalence point pH of approximately 8. Weak acids are used to titrate bases because the equivalence point is reached more slowly, so the results are more accurate. Phenolphthalein will be used to find the endpoint because it is colorless below pH 8, but turns pink just above pH 8.Concepts - Acid and Bases - Neutralization - TitrationProblem How can you use titration process to determine the strength of bases?Materials Goggles Buret Erlenmeyer flask, 250-mL Buret clamp Balance Ring stand Oxalic acid dihydrate (H2C2O4 • Sodium hydroxide solution (NaOH) 2H2O) pH unknown Distilled water 2 beakers, 100-mL Phenolphthalein Funnel Wash bottle Graduated cylinder 100-mL SafetyPrecautions Wear your goggles at all times during the investigation. Place the top of the buret below eye level when filling it to avoid splashing the solutions into the face. Place the buret and buret stand on the floor if necessary. Acids are corrosive and bases are caustic. Wipe up spills and drips immediately with wet towels, and the dry. Wash affected skin areas with cold water after any contact and notify your teacher. Burets are cumbersome and break easily – handle them with care. Procedure PartA.Preparation 1. Put your goggles on. While one lab partner prepares the oxalic acid (Steps 2 and 3), the other will prepare the buret for titration (Steps 4-8). 2. Determine the mass of a 250mL flask to 0.01g, the add 10. -1.5g oxalic acid dihydrate to the flask and determine the mass again. Caution:Acidsare corrosive.Avoidcontactwithskin,eyes,andclothing.Record these masses in Data Table. 3. Dissolve the acid in the flask with approximately 100mL of distilled water. Add two or three drops of phenolphthalein indicator solution to the flask.4. Make sure the buret is clean. If it is not, wash the buret with detergent and buret brush. Clean the tip by draining some detergent solution through it. Caution:Buretsarefragile.Usegreatcareinhandlingthem.5. Rinse the buret thoroughly with tap water, then rinse once with distilled water, draining final rinses through the tip. Clamp the clean buret to the support stand.6. Obtain 50-60mL of sodium hydroxide (NaOH) solution, unknown, in a 100 mL beaker. Position the buret so that the top is below your eye level and place and empty beaker under the buret tip to catch drips. Caution:Sodiumhydroxide iscaustic.Keepthetopoftheburetbeloweyelevelwhenpouring sodiumhydroxide.Avoidcontactwithskin,eyes,andclothing. Washspillsandsplasheswithplentyofwater.7. Pour approximately 5 mL of base into the buret. Drain this through the tip to remove water and coat the inside of the buret with base.8. Now fill the buret to slightly above the zero line. Drain some base through the tip to clear the buret tip of air. Stop between 0.0 and 2.0 mL. Remove the hanging drop at the tip by touching the tip to the inside of the waste beaker. Read the initial volume in the buret and record it in Data Table.PartB. Titration9. Place the flask with acid and phenolphthalein under the buret. The buret tip should be down about 1 cm insid ...