The masses I gathered from the weighing are as follows: Mass of boat and crystals first = 26. 88g Mass of empty boat after = 1.926g Actual amount of crystals = Mass of boat and crystals first Mass of empty boat after = 26. 88g 1. 926g = 24. 954g Now that I have the mass of the crystals used I will be able to calculate the number of moles of CuSO4 that I have by using the equation: Number of moles = Mass Molar Mass n = m Mr n = 24. 954 249. 6 n = 0. 099975961 mol Now I know how many moles of CuSO4 I have I can work out the concentration of the solution (CuSO4. 5H2O) I have made up with distilled water in the 1dm3 flask by using the equation:
Concentration = Number of Moles Volume c = n v c of CuSO4. 5H2O = 0. 099975961 mol 1 = 0. 099975961 mol dm-3 = 0. 100 mol dm-3 (3sf ) Due to the apparatus I used in the experiment there is a possibility that the concentration I have calculated is not exactly right; this is known as the precision error.
To calculate the precision error I need to calculate the percentage uncertainty of each piece of apparatus that I used and then add them all together to give a total percentage uncertainty: % uncertainty of the 3dp balance = (5 x 10-4) x 2 = 0.001 x 100 24. 954g = 4 x 10-3 % % uncertainty of the 1dm3 flask = 0. 8 x 100 1000 = 0. 08 % Therefore the total uncertainty = 0. 08 % + 4 x 10-3 % = 0. 084 % So, to work out the percentage error I need to work out the percentage of the concentration that could be incorrect: Percentage Error = Total uncertainty x Concentration 100 = 0. 084 x 0. 099975961 mol dm-3 100 = i?? 8. 397980724 x 10-5 Now that I have the percentage error I can show the possible errors that there could be in the calculation of the concentration of CuSO4.5H2O:
Highest possible c of CuSO4. 5H2O = 0. 10005994mol dm-3 Lowest possible c of CuSO4. 5H2O = 0. 099891981 mol dm-3 However I will represent the final concentration I have calculated of the CuSO4. 5H2O as: x 0. 099975961 i?? 8. 397980724 x 10-5 mol dm-3 0. 100 i?? 8. 40 mol dm -3 (3sf) The figures I used to calculate the errors from I obtained from the British Standard maximum permitted errors (tolerances) for volumetric glassware table from my chemistry laboratory. All of the glassware used is of grade B standard.