CHM 2045L- Equivalent Mass of an Acid 1 Equivalent Mass of an Acid Objectives: Upon successful completion of this laboratory the student will be able to: 1) Perform an acid-base titration accurately to an indicator endpoint. 2) Calculate moles from molarity and volume. 3) Write the complete, and net ionic equation for the neutralization of an acid with a base. 4) Calculate equivalent mass from total mass and moles of hydronium ion. 5) Write a formal scientific communication (laboratory report). Introduction: Titration is a simple and very frequently used technique of quantitative volumetric analysis, which is able to achieve great precision and accuracy when it is done properly. The titration apparatus is shown in Figure 1. It consists of a Burette (A), a clamp (B), a stand (C) and a container (D) in which the titration reaction occurs. The Burette has a valve (E) that allows precise control of the flow of liquid from the burette, and it has a thin tip (F) that produces small and very uniform drops. Figure 1, Titration Apparatus There is a solution that has a very precisely known concentration of one of the reactants in the Burette. This is called the titrant. The flask has an unknown amount of the other reactant, called the analyte. The analyte can be a known volume of a solution of unknown concentration, or it can be a carefully weighed http://chemwiki.ucdavis.edu/Analytical_Chemistry/Quantitative_Analysis/Titration/Acid-Base_Titrations https://www.google.com/#safe=off&q=analyte CHM 2045L- Equivalent Mass of an Acid 2 solid compound or mixture dissolved in a solvent. In this lab you will titrate a solid that you have weighed to the nearest 1 mg and then dissolved in water. Notice that the burette is marked the opposite way that a graduated cylinder is marked. It has the 0 mark at the top and the 50 mark at the bottom. Rather than being how much the burette contains, these marks represent how much has been removed from the burette, if the level starts at exactly 0.00 ml. What if you start titrating at some number other than 0? Then simply subtract your initial measurement from the final measurement. When you are reading a burette, just as with any other instrument, your measurement precision should go 1 decimal place past the smallest tic mark (Figure 2) Figure 2 How to read a burette The smallest tic mark on our burettes is 0.1 ml. This means that you will read the burettes to the nearest 0.01 ml. CHM 2045L- Equivalent Mass of an Acid 3 The number of moles of analyte present can be determined easily from the volume of the titrant, the concentration of the titrant in 𝑚𝑜𝑙𝑒𝑠 𝑙𝑖𝑡𝑒𝑟 (molarity, also abbreviated as M), and the balanced equation of the reaction between the titrant and the analyte. This can tell you a number of things. If you know the formula and molar mass of the analyte, it can tell you how many grams are present, a