The Gravimetric Determination of Calcium Abstract In this lab gravimetric analysis was used to determine the percentage of calcium carbonate in an unknown impure substance of calcium oxide Homogeneous precipitation was used along with weighing by difference vacuum filtration and le chatliers principle were all used to determine the final percentage in three different trials The final average percent of calcium oxide turned out to be 43 32 Introduction There are a few main objectives for this lab The first main objective is to understand the theory of gravimetric analysis which will be done experimentally using CaO Another concept in this lab is the use of homogeneous precipitation to crystallize a sample Finally the last main goal of this lab is to calculate the percent CaO in an unknown sample1 In this lab we will be creating a monohydrate salt by converting calcium carbonate to calcium oxalate This will be done and proceeds by the following reaction Ca2 aq C2O42 aq H2O aq CaC2O4 H2O s 1 A hot solution is used to form this monohydrate salt a salt which contains one H2O molecule per mole of the crystal This is done in a hot solution of ammonium oxalate rather than a cold one so that the di or trihydrate does not form Also it is in the presence of a very acidic solution so that the product is not exceeded and precipitation does not occur The main concept used in this lab is gravimetric analysis which uses masses of reactants and products to determine properties of a substance1 There are three main parts to the gravimetric analysis The first is the species must be converted to an insoluble compound The Ksp determines this The higher the Ksp the higher the higher the solubility The second is the compound must be pure and finally the final compound must be able to be measured These three concepts are the main necessities for the process of gravimetric analysis For isolation of crystals a slow filtration technique is necessary Most of the techniques in this lab emphasize slowness The slowness ensures that the regions of supersaturation which is contains more of a dissolved substance than is normally able under normal circumstances do not coprecipitate This is also so the crystals are large enough because the smaller the crystals the more unstable they are in the drying process which causes the loss of some of the crystals or water of hydration which is the hydrated water in the insoluble compound This again shows the necessity of slowness Weighing by difference is a concept to be used in this lab This technique is a very precise weighing technique and is used to ensure accuracy If this is done slow a small number of crystalline nucleation centers which is when droplets of water form a 2 crystal will form causing a better purity of the final product Urea in this case is added for the slowness or another substance can be added to ensure that the pH is slowly raised and so that the crystals are formed slowly The urea added is heated which causes the reaction to move forward showing le chatlier s principle which causes the pH to rise A hydrolysis reaction then occurs as shown in the next equation after the solution is heated NH2 2CO s H2O S CO2 g 2NH3 aq 2 The above reaction is a hydrolysis reaction which is a reaction that reacts in the presence of water This then reacts with the very acidic 1 pH solution to form ammonium in a neutralization reaction which is a reaction that neutralizes a base or acid and is as follows NH3 aq H aq NH4 aq 3 Then the H ions decrease and the reaction shifts to the right as shown HC2O4 aq C2O42 H aq 4 This is process is called homogeneous precipitation which is the process of generating crystals at a slow and homogenous rate The regions are localized and causes them to not form rapid small crystals In this process once the pH is raised to around 6 there are enough ions to form crystals After the crystals formed filtration of the crystals is used to carefully separate them and measure Even though some solutions may be very hydroscopic the one dealt with in the lab can be heated to lose the water in is because for complete combustion it must be heated until 500 C so a simple heating will not combust it These concepts are very often used in the real world One example of this is at Mawson Institute in Australia a Vacuum filtration system was used with gravimetric analysis to form flexible PEDOT thin films The gravimetric analysis was used to obtain the root source 2 Also in an experiment that the American institute for chemical engineers conducted the gravimetric analysis was used in an experiment used to determine effects of the heating rate in nanoparticles of thermite reactions The gravimetric analysis was used for the comparison of the nanoparticles and crystalline structures3 The use of monohydrate salts can also be seen in many different places in science The department of physics in the national institute of India performed one experiment that exemplifies 3 this concept A monohydrate salt was synthesized by a slow evaporation process similar to the gravimetric process4 Materials and Methods A detailed process for all materials and methods can be found in the lab manual1 Some slight deviations were made in this procedure For the beakers that the reactions took place in all three beakers were 400 mL beakers instead of 250 mL beakers due to the lack of 250mL beakers Beaker 3 held 3492g of calcium which confilicted with what the lab called for which was between 35 38g The other two beakers contained a sample that was within this range To beaker 1 1 2mL of HCl was added and then 2mL more 25 02g of urea was added and then 4 94g more Beaker 2 differed in that 2mL was added after the 1mL of HCl 25 5g of urea was added and then 4 98g extra was added also Beaker 3 differed in that 2 additional mL was added to the solution and 25 12g of urea was added and then an extra 5 2g was added During filtration for the first crucible 15 5mL of DI water was rinsed over the first time 15 1 the second time For crucible 2 the only deviation from the procedure was the first wash with water used 15 1mL rather than 15 For crucible three there were no deviations Results In the following table the results of the determination of the calcium are shown The unknown 112263 was given and the masses for each trial of this unknown are shown for each trial in Table 1 The amount of urea and HCl are shown these drove the reaction forward and caused the calcium hydrate The final mass of the