To know the procedure of measuring the accurate mass of a solid To calculate the number of moles of an unknown mass from its mass and molecular mass To know how to dilute a solution and the effect of dilution on the solution’s absorbance
Coloured solution – Potassium Manganate (KMnO4)
Part A: The Formula of Hydrated Copper (II) Sulfate
Firstly, about 1.0 g of hydrated copper (II) sulfate was put in the weighing bottle and the colour was noted. The mass of capped weighing bottle and hydrated copper (II) sulfate in it were measured and recorded. Then, the copper (II) sulfate was transferred into a casserole and the mass of the empty weighing bottle was measured and recorded. This method is necessary as to ensure the mass of copper (II) sulfate is mostly accurate and as to reduce the chance of spilling the chemicals while weighing it.
Next, the copper (II) sulfate in the casserole was heated using a hot plate until the colour turned as a pale blue. After that, the casserole was removed from the hot plate and it was allowed to cool down.
After a while, the content of the casserole was transferred back into the weighing bottle and its mass was measured and recorded again as to get the mass of dehydrated copper (II) sulfate which was in white.
Part B: Dilution of a Coloured Solution
A beaker was used to collect roughly about 20cm3 of the coloured solution. About 10 cm3 of the coloured solution was transferred into a volumetric flask using a pipette and deionized water was added until it reached the mark. The mixture was then shaken well. Before the coloured solution was measured for its absorbance, deionized water was first placed in the ultraviolet-visible (UVV) spectrophotomter as to calibrate the UVV spectrophotometer to zero. Then only some of the diluted solution in the volumetric flask was transferred into a cuvette cell using a dropper and its absorbance was measured and recorded. After...
References: Silberberg M.S 2006, Chemistry- The Molecular Nature of Matter and Change, 4th edition, McGraw-Hill, New York.
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