1 STANDARIZATION OF A BASE AND TITRATION OF A VINEGAR SOLUTION ADDITIONAL READING The concepts in this experiment are also discussed in sections 3.6 AND 17.3 of Chemistry and Chemical Reactivity by Kotz, Treichel, Townsend and Treichel, and in sections 4.3b, 17.3a, and 17.3b of Mindtap General Chemistry by Vining, Young, Day, and Botch ABSTRACT This experiment is divided into two parts. Each student is expected to perform the experiment individually. In Part A, you will prepare a NaOH titrant solution, then standardize it (determine its exact concentration) using the acid primary standard, potassium hydrogen phthalate, KHC 8 H 4 O 4 , frequently abbreviated as KHP. Note KHP is not a chemical formula . In Part B you will use your standardized NaOH solution to determine the molar concentration of vinegar (an acetic acid, CH 3 COOH, solution), and convert this concentration unit to a mass percent concentration unit, and finally compare your measured mass percent concentration to the value reported on the bottle. BACKGROUND T ITRATIONS One of the most useful strategies in analytical chemistry is to use a known reagent (known composition or concentration) as a standard to analyze an unknown substance. A titration is an analytical procedure in which a solution of known concentration, the standard solution, is slowly reacted with a solution of unknown concentration. The concentration of the unknown solution can be easily calculated. Titration is often used to measure the concentration of an acid or base, but it can also be used for any chemical reaction if the stoichiometry is known. EXPERIMENTS 6 AND 7 ARE BOTH ACID BASE TITRATION EXPERIMENTS, QUITE SIMILAR TO EACH OTHER. THE REASONS FOR DOING TWO TITRATION EXPERIMENTS A. TO GIVE STUDENTS PLENTY OF OPPORTUNITY BOTH TO PERFECT THEIR TITRATION TECHNIQUE AND TO LEARN TO DO THE CALCULATIONS; B. TITRATION IS THE MOST IMPORTANT TECHNIQUE LEARNED IN CHEM 1033 LAB. YOU WILL DO A PRACTICAL LAB EXAM AT THE END OF THE SEMESTER; IT WILL BE A VERY SIMILAR TITRATION. IT IS IMPORTANT TO REALIZE THAT TITRATION IS AN ACQUIRED SKILL, REQUIRING PRACTICE. MOST STUDENTS ARE NOT PROFICIENT AT FIRST, BUT IF YOU WANT TO BECOME EXPERT AT IT, YOU WILL GET THERE WITH PRACTICE. It is critical that there be an observable change that signals that the titration is complete. This is called the endpoint , since it signals the end of the titration, when the equivalents of titrant added just equal the equivalents of the analyte unknown. When performing an acid-base titration, we commonly use an acid-base indicator that has one color before the endpoint but changes sharply to a different color at the pH of the endpoint. Titrations are carried out using a specialized piece of glassware called a buret, which is long tube with a dispensing valve.
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- Spring '08
- Chemistry, Sodium hydroxide, KHP