Gravimetric analysis is used to determine the amount of water in a sample of copper sulfate in this case. Three procedures are to be followed during the experiment; the first one helps determining the quantity of copper ion in the hydrated copper sulfate, then, determining the amount of water in the sample thanks to the second procedure, and finally, analyzing the sulfate ion present in the sample using the third procedure. In gravimetric analysis, a solid product is formed after reacting a compound with another material. The composition of the sample can then be easily deducted because the composition of the solid product is already known.
In the first procedure (A), hydrated copper sulfate is reacted with oxine, during the second one (B), the sample is heated to determine the amount of water it contains, while deduction will be used in the third procedure (C), to determine the quantity of sulfate in the sample of hydrated copper sulfate.
The first procedure consists of analyzing copper ion in hydrated copper sulfate. First, a hot plate is turned on and heated to 70°C, in the meantime, 0.3g of Cux(SO4)y . zH2O is collected and poured into a 250ml beaker, then, 100ml of distilled water is added to dissolve Cux(SO4)y . zH2O. One gram and a half of ammonium acetate is also added to the beaker, and then 5ml of glacial acetic acid is poured in the same recipient. The beaker is placed on the hot plate, and the temperature is checked using a thermometer. While the beaker is on the plate, 3% 8-hydroxy-quinoline (oxine) is gradually added to the beaker and simultaneously stirred using a glass stir rod until a precipitate appears. The mixture is then stirred for about 5 minutes, while another beaker of distilled water is heated over a second plate for filtration. After 5 minutes have elapsed, the mixture is left to allow settlement of the green-yellow precipitant. Using gravity filtration, the mixture is slowly filtered through a foiled cone-shaped filter paper. After it is complete, the precipitate is transferred to a small beaker covered with perforated aluminum foil. The beaker is left for a week so that the precipitate completely dries; after this period of time, the precipitate is filtered by weighing the filter paper with the precipitate, then subtracting the mass of the filter paper.
Then comes the second procedure in which the amount of water in the sample is analyzed. First, a meeker burner is lighted and the ring clamp is set 4-6 inches above the flame to avoid overheating or damages to the crucible, then a clean crucible is heated for 5 minutes and allowed to cool down over a ceramic tile for 15 minutes. After the crucible is weighed, it is filled with 2g Cux(SO4)y . zH2O, and placed back over low flame for 15 other minutes with the lid partially covering it.
The flame is then turned off, and the crucible completely covered and left to cool down, then it is weighed. The sample is heated again for 5 more minutes, and the weighed. This procedure is repeated until two consecutive mass measurements differ by not more than 0.1g. The mass loss after heating determines the quantity of evaporated water that was previously present in the sample before heating.
The last procedure is done by deducting the percent of sulfate in the Cux(SO4)y . zH2O sample. Knowing that the sample contains copper, sulfate, and water, and having the previously calculated percent of copper and evaporated water from A and B procedures, the percent of sulfate can be determined by difference, therefore, no experiment is needed for the last procedure (C).
DATA AND RESULTS
During the first procedure, the mass of the precipitate was 0.183g. Knowing that 0.364g of Cux(SO4)y . zH2O (A1) and 1.003g of dry Cu(C9H6ON)2 were calculated, the mass was deduced using the following equation (A3), then, the Cu percent was determined using = 50.27% (A4).
In procedure B, the crucible alone weighed 27.350g (B1), and 29.358g with the Cux(SO4)y . zH2O sample (B2), Cux(SO4)y . zH2O sample equals B2-B1 = 2.005g (B3). Moreover, the heated crucible plus the Cux(SO4)y sample weighed 28.919g (B4), therefore the amount of lost water was B2-B4 = 0.613g, its percent equals = 30.6% (B6).
Therefore, SO4 percent in the Cux(SO4)y . zH2O sample is = 19.13%.
The three procedures (A), (B), and (C), performed during the experiment permitted the analysis of the hydrated copper sulfate sample, thus determining the percent of each of its components, that is, water (30.6%), copper (50.27%), and sulfate (19.13%), on the initial sample of hydrated copper sulfate. Using this data, the ratio could also be deduced, ratio of H2O/Cu(SO4)approximately equals 6, therefore, x=1, y=1, and z=6, meaning a ratio of 1:1:6.