How to do Gravimetric Analysis in Chemistry (with calculations and examples!)

Jason Neal, a chemistry teacher, introduces the concept of gravimetric analysis in this video. He explains that gravimetric analysis involves determining the concentration of a solution through laboratory techniques. The video begins with a disclaimer about safety precautions, emphasizing the importance of wearing chemical splash goggles in the lab. Jason then explains the concept of solution concentration, measured in molarity, using a saltwater solution as an example. He clarifies that the concentration of a solution remains the same regardless of the amount taken, setting the stage for the experiment on potassium iodide solution concentration determination.

In this paragraph, Jason Neal proceeds with the gravimetric analysis experiment by preparing a filter paper into a funnel shape and moistening it with distilled water. He then takes approximately 9.45 milliliters of potassium iodide solution and adds it to a larger beaker. To ensure all potassium iodide is transferred, he rinses the graduated cylinder with distilled water three times, highlighting that this process does not change the moles of potassium iodide. The goal is to fully transfer the potassium iodide to the beaker for the next steps of the experiment.

Here, Jason Neal describes the reaction between potassium iodide and lead nitrate, which results in the formation of lead iodide particles. He adds lead nitrate to the potassium iodide solution to ensure all iodide ions react. The yellow lead iodide precipitate formed is then filtered using the prepared filter paper. Jason emphasizes the importance of rinsing the beaker and precipitate with distilled water to remove any remaining ions, leaving only the lead iodide precipitate on the filter paper. This process is crucial for accurately determining the moles of potassium iodide in the original solution.

After the filtration process, Jason Neal discusses the next steps of drying and weighing the lead iodide precipitate. He carefully peels the filter paper from the funnel and spreads the precipitate to dry, either overnight or in a drying oven. Once dried, he weighs the precipitate along with the filter paper and subtracts the mass of the empty filter paper to find the mass of the lead iodide alone. This mass is then used to calculate the moles of lead iodide, which will be further used to determine the moles of potassium iodide in the original solution.

In the final paragraph, Jason Neal concludes the gravimetric analysis experiment by calculating the molarity of the potassium iodide solution. Using the mass of lead iodide obtained from the previous steps, he calculates the moles of iodide ions, which is twice the moles of lead iodide since each molecule of lead iodide contains two iodide ions. With the moles of iodide ions determined, he equates this to the moles of potassium iodide in the original solution. Dividing these moles by the volume of the solution in liters, he arrives at the molarity of the potassium iodide solution, demonstrating the effectiveness of gravimetric analysis in determining the concentration of an unknown solution.