The Gravimetric Determination of Calcium Abstract The purpose of this experiment was to determine the calcium content of an impure sample of calcium carbonate by converting the calcium to solid calcium oxalate monohydrate This experiment helps teach us the theory behind gravimetric determination as well as how to use a homogeneous precipitation to crystallize a sample Heating plates analytical balances and a vacuum filtration system were used throughout this lab The heating plates were used in this lab so that the reaction would form the desired monohydrate instead of the bi or tri hydrates that form in cold settings The analytical balances were used in the weighing by difference technique Lastly the vacuum was used in the filtration of our calcium oxalate monohydrate precipitate With the use of these techniques the percent CaO in our unknown was found to be 44 07 Introduction The point of this experiment was to develop an understanding of gravimetric analysis to learn how to determine the percent CaO in an unknown sample and to gain the ability to use precipitation to crystallize a sample In order for a procedure to be considered gravimetric it must exhibit a quantitative conversion of a species into a isolatable compound the precipitate must be of known purity and the precipitate must be in a form that can be easily weighed and handled At the beginning of the lab you have to implement the weighing by difference technique In order to weigh by difference you have to first fill the weigh bottle with the desired amount Then you record the weight of the bottle and its contents Once the contents have been removed from the weigh bottle you record the weight of the empty weigh bottle and subtract that from the weight found for the bottle and its contents This technique is important because it takes into account the amount of substance that sticks to the weigh bottle The chemical significance of gravimetric determination that holds chemical significance is the conversion into an isolatable compound This lab in particular uses the following reaction to convert calcium to a large isolatable crystal Ca2 aq C2O42 aq H2O l CaC2O4 H2O s After the precipitate is formed we have to filtrate it out of the solution We did that in this lab by pouring the solution through a vacuum filtration system The crucibles are able to catch the large crystals that were formed while allowing the liquids to be drained through them One thing that s important is the formation of a homogeneous precipitate We did this by controlling the pH of the starting solution to be 1 The pH of the solution was then raised slowly by heating the solution containing urea to produce ammonia One real life example of gravimetric determination would be the calculation of carbon dioxide dissolved in water Incidents can occur if this isn t properly monitored Therefore amount of carbon dioxide in water needs to be verified to meet a specification so that it is safe to be used in boilers1 Materials and Methods Three glass crucibles were labeled AW 1 AW 2 and AW 3 using pencil Then the crucibles and the calcium carbonate was dried for one hour at 110oC The crucibles and the calcium carbonate were dried by putting two of the crucibles into a 400 mL glass beaker and the calcium carbonate along with the third crucible into a 150 mL beaker These two beakers were covered with watch glasses and heated at 110oC for an hour Then using tongs the crucibles and calcium carbonate were placed in a desiccator to cool to room temperature The crucibles were then cleaned with Kimwipes to remove any smudges that would alter the mass of the crucibles After the crucibles were cleaned they were weighed to the tenth of a milligram using an analytical balance Crucible 1 weighed 31 3676g crucible 2 weighed 30 5278g and crucible 3 weighed 32 1995g A 250 mL beaker another 250 mL beaker and a 400 mL beaker were respectively labeled 1 2 and 3 0 35 grams of the unknown calcium carbonate was placed in each of these beakers The mass of the unknown calcium carbonate was recorded to the tenth of a milligram using the weighing by difference technique 100 mL of deionized waster was added to each of the three samples Then 6mL of 6M HCl was slowly added to each beaker while swirling the solutions The pH of the sample was then tested using pH paper Because the pH was greater than one still several drops of HCl were added to the solutions to lower their pH Four drops of methyl red indicator were then added to beaker 1 2 and 3 20 mL of saturated ammonium oxalate solution was placed in three 50 mL beakers 1 0 mL of 6M HCl was added to these beakers using a Mohr pipet The three 50 mL beakers were mixed by swirling The pH of these three beakers was verified to be less than one using pH paper One of the 50mL beakers was added to each beaker 1 2 and 3 Next 25 g of solid urea was added to each of the numbered beakers The numbered beakers were then mixed by swirling The solutions were then covered with Para film to save for the second lab period At the beginning of the second lab period Beaker 1 was covered with a clean watch glass The solution was then heated to near boil using a hot plate until the methyl red indicator changed from pink to yellow Note that the solution was not allowed to actually boil Also note that the urea released gas bubbles when heated but these looked different than boiling This process took about 35 minutes When the color did not change within this time period 5 g of urea was added and the solution was swirled When the color still did not change after an additional 10 minutes 5 more grams of urea were added This process was repeated every 10 minutes from this point until the color changed The condensation on the watch glass was then rinsed into the beaker using a wash bottle A filtration system was assembled according to the diagram in the lab manual using two flasks two clamps heavy wall vacuum hose an aspirator and a sintered glass crucible Beaker tongs were used to pour the hot solution into the sintered glass crucible labeled 1 A rubber policeman and a small amount of deionized water were used to transfer the precipitate completely into the crucible Because boiling occurred in the suction flask the filtration of the solution occurred over a six minute time period The procedure above that occurred during the second lab period was repeater for beakers 1 and 2 Next the crystals from the crucible 1 were washed with 15mL of ice cold deionized water After all