Gravimetric Analysis Lab Procedure

The first paragraph outlines the initial steps in a gravimetric analysis experiment. The process begins with weighing out approximately two grams of either potassium or sodium carbonate, referred to as 'salt'. The importance of accuracy in weighing is emphasized, though it is acknowledged that precision to the exact gram is not necessary. The salt is then added to a weighing boat, which becomes part of the scale's tare. The experiment requires pre-dissolving the salt to ensure complete dissociation of the metal (potassium or sodium) and carbonate ions. Distilled water is added to the beaker, with an estimated volume of 200 milliliters, though the exact volume is not critical as the molarity is not the focus of this lab. The goal is to dissolve all the salt completely, allowing the metal and carbonate ions to dissociate fully. The explanation includes a discussion of solubility rules and the interaction between light and the dissolved ions, which are too small to be detected by the naked eye once dissolved.

This paragraph details the continuation of the gravimetric analysis experiment by focusing on the precipitation reaction. The next step involves adding calcium chloride to the dissolved salt solution. The calcium ions (Ca^2+) from the calcium chloride will react with the carbonate ions (CO_3^2-) to form a precipitate, following Coulomb's law which predicts the attraction between ions of opposite charges. The goal is to ensure that the reaction goes to completion by adding an excess of calcium chloride, calculated to be around 125 milliliters for two grams of salt. The paragraph emphasizes the importance of having more than enough calcium chloride to react with all the carbonate ions present. The formation of the precipitate is visually described, noting how light interacts with the crystal structure of the calcium carbonate, making it visible to the observer. The process of settling and filtering the precipitate is then discussed, with the aim of collecting all the mass of the carbonate for further analysis.

The third paragraph describes the process of filtering and washing the precipitate formed in the previous steps. The experimenter uses a filter paper and a Büchner funnel with an aspirator to create a partial vacuum and filter out the precipitate. The importance of collecting all the precipitate and ensuring a clean filtrate is stressed, as every mole of carbonate is critical to the experiment's outcome. The paragraph also addresses potential issues such as spilling or not collecting all the precipitate, which could lead to inaccurate results. The experimenter may need to repeat the filtration process several times to ensure that all the precipitate is collected. The use of a rubber policeman (a glass rod) is suggested to help push out the solids during the filtration process. The goal is to end up with a clear filtrate and all the precipitate collected on the filter paper.

The final paragraph focuses on the steps taken after the filtration process. The precipitate-laden filter paper is carefully removed and placed on a watch glass for drying. The dried filter paper with the precipitate is then placed in an oven to be weighed the following day. The importance of accurate record-keeping is highlighted, as the mass of the precipitate on the filter paper is crucial for determining the moles of carbonate and, by extension, the moles of the original metal carbonate. The drying process ensures that the mass measured is representative of the precipitate alone, without any residual water. The paragraph concludes with the anticipation of obtaining the mass of the precipitate and using this data to complete the analysis of the experiment.