In this experiment we hope to find the formula of a compound – a yellow compound formed when copper reacts directly with iodine vapour.
Copper Strip, emery paper, dry filter paper, access to a balance, iodine crystals, boiling tube and a Bunsen burner.
We took a strip of copper and cleaned it with emery paper. Following this, we weighed the strip on a top pan balance. We placed the strip of copper into a boiling tube with the end bent around the lip of the boiling tube. This left the copper strip suspended above the iodine crystals which we placed into the bottom of the boiling tube.
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Using tongs, we carefully heated the boiling tube in the centre, making sure that the flame did not align directly onto the iodine crystals as this would cause the gas to escape quickly. The experiment was carried out with the aid of a fume cupboard as iodine gas is harmful. A purple gas was emitted from the iodine crystals when heated and as the experiment continued, an obvious change in colour of the copper strip was apparent. We continued to heat the boiling tube until no purple gas was seen.
Mass of copper that has reacted with the iodine: 0.141g
Mass of iodine it reacted with: 0.276g
No. of moles of copper atoms reacted (Ar Cu=63.5): 0.0022205
No. of moles of iodine atoms reacted (Ar I=127): 0.0021732
No. of moles of iodine atoms that combine with one mole of copper atoms: 64.88M
After gaining the results, it is clear that there is considerable room for error in this experiment. For example, it was difficult to remove all of the copper iodide from the copper and there would almost certainly be some left on the copper. This would result in the final mass of the copper being slightly increased. Another error may have been that we lost a substantial amount of the purple vapour while heating the test tube and this would affect the amount of copper iodide formed on the copper.
Uncertainties, or experimental errors, would include the weighing of the masses. When weighing the masses of the copper strip, the copper iodide, etc. we used top-pan balances. Top-pan balances round off masses to a certain degree of accuracy and our balances read off at 2dp. The experimental error here is that there is a small space for error to occur in the rounding off process. This is called percentage error.
Percentage error = error x 100
Therefore : 0.005g x 100 = 0.04%