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Final Exam Review CHEM120L Final Exam summary - includes reactions and experiments summaries.

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University of Waterloo
Sue Stathopulos

CHEM 120L review notes (Final Exam) Experiment #1 – The Chemistry of Copper Compounds - Know the equations of the reactions involved: Part 1 – synthesis of copper (II) nitrate and copper (II) hydroxide. - Put solid copper wire into a 250mL beaker and add 10mL of HNO solution i3to the beaker under the fume hood. The reaction of Cu with nitric acid (HNO ) 3 Cu (s)NO 3(aq) CuNO 3(aq) NO 2(g)+ 2H 2 (g) Chemically: The copper ions were dissolved into the nitric acid and formed a blue solution. Nitrohen dioxide and water vapour was released. This is an oxidation-reduction reaction. Physically: The solution began to fizz, showing the release of gases (NO and H2O) nitr2c dioxide and water vapour. The solution began orange-green with many precipitates (Cu ) and the(s)nal solution was clear blue. (CuNO 3(aq) - After dissolution is complete dilute with 25mL deionized water, then add 25mL of 20% NaOH solution. The formation of Cu(OH) 2 Cu(NO )3 2(aq) 2NaOH (aq) Cu(OH) 2(s)+ 2NaNO 3(aq) heat Chemically: This is an exothermic double-displacement, precipitation reaction. The nitrate ions are displaced by the hydroxide ions, forming copper (II) hydroxide. Physically: After NaOH was added, the solution became hotter (exothermic!) and many black precipitates formed. These precipitates are Cu(OH) (we2know this because Cu(OH) is NOT so2uble (refer to solubility rules) and therefore will precipitate out of the solution as a solid) The density of the solution increased (makes sense since more copper (II) hydroxide is being precipitates out, more precipitates  thicker solution) Part 2: Synthesis of Copper (II) Oxide - Why don’t we separate copper (II) hydroxide? – because since it’s so thick it would take too long to separate through the filter paper and then washing the filter paper with soluble salts would be time consuming and not very effective - Instead, we can turn copper (II) hydroxide to copper(II)oxide, which is thinner (and therefore easier to separate) How to separate Copper (II) Oxide? – boil it. Boiling it will cause ALL the Cu(OH) 2(aq)o turn into black CuO .(s) Cu(OH) + heat  CuO + H O 2(aq) (s) 2 (l) (* if the Cu(OH) is not turning black, add another 25mL of NaOH and continue heating) Quantitatively transfer (to transfer all of the substance from one place to another place) all the CuO into the Buchner Funnel (funnel used to vacuum filtration, it is made of thick glass so that it won’t shatter from the vacuum pressure. NEVER use erlenymer flasks, volumetric flasks or other flasks with thin glass) and by vacuum filtration (separating a solid from a solvent or a liquid reaction mixture. A piece of filter paper is put on top of the Buchner funnel and the solution is allowed to pass through the filter paper by sucking it in by vacuum pressure. When you are finished drying, turn off the tap for vacuum and carefully remove the filter paper with the solid on it. *safety precautions of vacuum filtration: make sure that there are no cracks in the Buchner Funnel because cracks would cause the funnel to crack and explode violently under pressure. Once you have checked that there are no crack, make sure the vacuum line is working by putting your thumb over the vacuum line and seeing if there is vacuum pressure. The connect it to the vacuum flask AKA side arm flask (you may need to wet it to get it to fit on tight) then place the Buchner Funnel on top of the vacuum flask tightly by using a rubber stopper. To check the entire system for good suction, place your hand (without gloves on) over the Buchner funnel, if you feel the suction, then its working properly, if you don’t check to make sure that the rubber stopper and the vacuum line are sealed tightly on or any leaks and cracks. When pouring the solution into the Buchner funnel, pour it slowly to avoid making the filter paper rise up, causing the solution to pass UNDER the filter paper and directly through to the vacuum flask, if this happens you need to do everything again.) The solution should never fill more than two-thirds of the Buchner funnel. Rinse the beaker that originally held the CuO by adding 1(s) of deionized water and rinsing it 3 times (ie: rinse the beaker 3 times with 10mL of deionized water) – the purpose of this is to displace the NaOH and NaNO in t3e solution with water so that we are left with CuO and H O  will be (s)en out 2y (l) vacuum filtration. - After this is all done, we will have isolated the CuO (s) Part 3 – Synthesis of Copper (II) Sulphate Now we want to convert the CuO to CuSO by (s)ing H SO h4wever since CuSO2is 4oluble, it will 4 2+ - dissociate, leaving us with Cu ions and SO ions, which4is what we want – we want to recover the copper. - Transfer the CuO on the filter paper into the original 250mL beaker that we began with. Then (s) wash the remaining CuO left on the filter paper into the beaker by using H SO . Then wash the (s) 2 4 H SO that remains on the filter paper by using 10mL of deionized water. 2 4 *if the CuO do(s)not dissolve completely in the H SO heat the so2utio4, boil gently until the solution has turned blue. If there are still precipitates after this, it is probably because not enough H 2O h4s been added, decant the supernatants into a 100mL beaker and add a small amount of H 2O t4 this beaker, if it turns blue then you can add it to the 250mL beaker. Use 5mL of water to rinse the H SO2out4of the beaker. Equation: CuO + H SO + 3H O  Cu(H O) 2+ + SO 2- (s) 2 4(aq) 2 (l) 2 4 (aq) 4 (aq) Chemically: 2+ 2- H 2O 4(aq)is soluble because SO is so4uble, therefore it will dissociate into H + SO . 4 The steps are... CuO +(s)SO 2 4(aq) H O2 CuSO + H O 4 H O 2 this s2ows us that it is an acid/base reaction But since SO is 4oluble, the compounds containing SO will dissociate4when in an aqueous solution (like in this one) CuO +(s)SO 2 4(aq)+ H 2  Cu + SO2+ 42-+ 2H O2 2+ 2- CuO +(s)SO +23H O4 Cu(H2O) 2 4 (aq)+ SO 4 (aq) Physically: When the H SO 2as 4dded to the CuO, the solution turned aqua, the same colour that it was initially. However there were still some black precipitates present, to get rid of these, the solution was boiled and all the black CuO disappeared. This is an acid/base reaction. - Reasoning for this: the CuO is dissociated into its ions when it is done reacting with SO 4 therefore it is completely dissolved into the solution and we can no longer see it, and it goes back to its original colour when we had copper dissolved into a solution. Part 4 – Recovery of Copper - Zinc is more chemically reactive than copper so i
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