Experiment 4 Gravimetric Analysis of a Chloride Salt Aim • To illustrate typical techniques used in Gravimetric Analysis by quantitatively determining the amount of chloride in an unknown • Introduction: • Two common methods used in analytical chemistry -a gravimetric analysis, -volumetric analysis. Gravimetric analysis derives its name from the fact that the constituent being determined can be isolated in some weighable form. Volumetric analysis derives its name from the fact that the method used to determine the amount of a constituent involves measuring the volume of a reagent. • Chloride ion may be quantitatively precipitated from solution by the addition of silver ion according to the following ionic equation: Ag+(aq) + Cl−(aq) → AgCl(s) • The addition of a silver nitrate solution to an aqueous solution containing chloride ion precipitates AgCl quantitatively • The precipitate can be collected on a filter paper, dried, and weighed. • From the mass of the AgCl obtained, the amount of chloride in the original sample can then be calculated. Procedure: 1. Obtain an unknown and record its number on your report sheet. 2. On a weighing dish, weigh to the nearest 0.0001 g about 0.2 of your unknown sample. 3. Transfer the sample quantitatively to a clean 150-mLbeaker (do not weigh the beaker) and label the beaker #1 with pencil. Record the sample weight. 4. Add 100 ml of distilled water and 1 ml of 6 M HNO3 to the beaker. 5. Using a glass rod, stir the solution until all of the sample has dissolved. Leave the stirring rod in the beaker. Do not place it on the desktop. 6.While stirring the solution, add to it about 10 ml of 0.5 M AgNO3 solution. Place a watch glass over the beaker. White ppt will be formed 7.Obtain a filter paper and weigh it accurately. Fold it and place it in the funnel so that one side has three folds and the other side has one fold of paper against the funnel. 8.Wet the paper with distilled water to hold in place inside the funnel. Transfer all the precipitate and solution from the beaker onto the filter paper using a rubber policeman and a wash bottle to wash out the last traces of precipitate. 9. Wash the precipitate on the filter paper with two or three 5-mL portions of distilled water from the wash bottle. 10.Finally, wash with 5-mL of acetone. 11.Repeat the above steps with the other two samples. 12 place the sample in the oven (ask your instructor ).