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# formula for copper sulphate

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Introduction

Determination of the formula of Hydrated Copper Sulphate Crystals. Skills A and E Experiment 1 Mass of crucible: 28.54g Hydrated Copper: 2.40g Total: 30.94g After heating, Hydrated Copper = 1.60g Reheat after 5 minutes, mass: 1.59g Reheat after 5 minutes, mass: 1.58g Reheat after 5 minutes, mass: 1.57g final mass of hydrated copper Aim: Calculate the percentage by mass of water of crystallisation present in the crystals. 2.40 - 1.57 = 0.83 / 2.40 x 100 = 34.6%. Experiment 2 Aim: Use equations 1 and 2 to deduce the relationship between the number of moles of Cu2+ and the number of moles of S2O32- . Results Table Burette Readings Trial (cm3 ) Initial (cm3 ) Final (cm3 ) Volume used cm3 (final - initial) 23.75 0.00 23.90 23.90 0.00 23.85 23.85 0.00 23.80 23.80 0.00 23.90 23.90 Average titre Volume (cm3) : 23.86 It is a 2:2 ratio; the number of moles of Cu2+ is proportional to the number of moles of S2O32- . Sodium Thiosulphate: Number of moles = concentration x volume / 1000 0.1 x 23.86 / 1000 0.0024 Aim: Calculate the percentage by mass of Cu2+ in your sample of copper sulphate crystals. Copper Ion: Mass = Number of moles * Relative formula mass 0.0024 * 63.5 0.1524grams * 10 = 1.524 / 5.80 * 100 = 26.3% Analysis of the results from both experiments (Skill A) ...read more.

Middle

Also, using pipette filler, air bubbles may have been formed at the tip as the solution was being drawn. This would have affected the quantity of solution being titrated, as it would have appeared to be less. If air bubbles do occur, then the solution should be released back and the process should be started again. In terms of procedural errors for Experiment 2, if the reading is not taken from the bottom of the meniscus, then an inaccurate reading is taken, so this would lead to an error being created in the procedure. Also, in terms of the end-point of the experiment, it is every easy to over-titration and this may have been the case, so end-point should be approached with care and the 30 seconds wait should be kept to make sure that the colour change is permanent. In addition, for the procedural error of Experiment 1, it was not repeated more than once so therefore, an average could not be found which mean that the one experiment that was conducted had to be taken as the true final mass. Also, the weighing scale measures to a degree of two decimal place; if it measured to four, this may have made the experiment more accurate. ...read more.

Conclusion

This shows that the titration method is more accurate. The mole ratios remained the same because of the relationship between the water and copper, however, there were small variations in the trials which could have been caused by the lack of drying of the Copper or improper calibrated weighing scales. Looking at the method critically, with titration, over-titration has to be avoided. The colour change observed at the end is a little requirement but this has to be performed carefully so that it does not affect the result. In addition, the stir motor should not be allowed to run too fast because splashing may occur therefore, the reagents will not mix in. Whilst saying this, the burette should be centered over the flask so that drops fall directly into the solution otherwise, drops may fall to the side of the flask affecting the volume, thus, the reliability. A main improvement that could be implemented had the equipment been available would be to completely automate the experiment to remove the degree of human error. This would involve using very accurate robotic machines to precisely measure the amount of copper sulphate used and the mass of everything. It would also heat it for the exact amount of time to prevent burning (oxidization) or to not be fully dehydrated. Reference http://www.avogadro.co.uk/miscellany/titration/titreset.htm http://www.br.cc.va.us/turner/Chm111/reading_the_buret_and_titration%20technique_.htm ...read more.

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