Students use titration to determine the chemical properties of unknown liquids.
Titration is a process that students use to calculate the concentration of an unknown solution by making it react with a substance of a known concentration. This method is typically used to find the pH level of a substance of unknown concentration. The process is completed by adding small amounts of a liquid of known concentration to the unknown substance. While doing this experiment, the liquid of the known concentration is called titrant, and the substance the concentration of which is not known is called titrand or analyte.
Finding Concentrations
Students take a small quantity of the substance they want to identify, and put it into a small beaker or flask. At the beginning of the experiment, students measure the pH of the unknown liquid. Students then incrementally add of titrant to the unknown solution, taking pH readings after each step. They plot the changing pH of the solution versus the amount of titrant added. At the end of the experiment, students use the volume of the titrant used, and information on its concentration and the resulting pH level to calculate the concentration of the titrand.
Determining Acid Strength
For this experiment, students fill a buret with sodium hydroxide solution (NaOH). Students then place a defined quantity of vinegar, which contains acetic acid, into a beaker. By using the steps defined above, students can identify the concentration of acetic acid in the vinegar. As they add small amounts of NaOH to the vinegar, the pH level of the household acid changes, and when the experiment is over, students can calculate the concentration of acetic acid in the vinegar. By performing the experiment a number of times, with various types of vinegars, they can study the acidic concentration of this common household product.
Evaluating Fruit Juices
Fruit juices are also a naturally occurring acid. Orange juice is slightly acidic, as are juices from other citrus fruits. The titration process allows students to measure and identify the concentration of acids in common fruit juices. Because vitamin C is found in acidic fruit juices, the experiment can also be used to determine the amount of vitamin C in a fruit juice.
Evaluating Antacids
When the concentration of an acid is known, titration can determine how much antacid is required to neutralize an acid, as well as determine the strength of the antacid material. In this experiment, students take an antacid tablet and crush it with a pestle and mortar. Students take equal amounts of the antacid, and mix it into a solution so that the experiment can be completed a number of times. In this case, rather than titrating the solution with a base such as NaOH, students use hydrochloric acid (HCL) of known concentration as the titrant. By adding incremental amounts of HCL to the crushed antacid tablet solution, students can calculate the strength of the antacids. Students can use this project with multiple brands of antacids to determine the strength of various antacids and predict their effectiveness.
Tags: experiment students, known concentration, , calculate concentration, small amounts