Date Pre-lab Questions hemical Reactions of Copper 6 Pre and Percent Yield hls e

Question

Date Pre-lab Questions hemical Reactions of Copper 6 Pre and Percent Yield hls esperiment in the latoratory ywou eampl you should be able to answer the Befor following questions. o tis experiment in the laboratory, you she 1. Give an example, other than the , other than the ones listed in this experiment, of redox and metathesis reactions. 2. When will reactions proceed to complot 3. Define percent yield in general terms 4. Name six methods of separating materials. 5. Give criteria in terms of temperature changes for ex othermic and endothermic reactions 6. If 3.35 g of Cu(NO,)2 Ir 3.35 g of CuNO,) are obtained from allowing 2.25 g of Cu to react with excess HNO,, what is the percent yield of the reaction? 7. What two liquids are flammable in this experiment? pyright C 2015 Pearson Education, Inc.

Explanation / Answer

1. A redox reaction would be the reaction of hydrogen and fluorine to give hydrogen fluoride, in which hydrogen is being oxidized and fluorine is being reduced:

H2 + F2 2 HF

An aqueous methatesis reaction, where silver chloride is precipitated from a mixture of sodium chloride and silver nitrate:

AgNO3 (aq) + NaCl (aq) AgCl (s) + NaNO3 (aq)

2. A reaction will proceed to completion when a given condition is present for it to be complete, i.e. the formation of a gas, the presence of a precipitate or the formation of a slightly ionized substance like water.

3. The percent yield of a reaction, in general terms, measures the reaction's efficiency. It is defined as the ratio between the actual yield and the theoretical yield of the reaction.

4. Without making a distinction between physical and chemical methods: filtration, decantation, centrifugation, sieving, electrolysis, distillation.

5. In terms of temperature changes, an exothermic reaction will increase the temperature as it releases energy, while an endothermic reaction will decrease the temperature as energy is absorbed.

6. We first write the balanced equation:

3 Cu + 8 HNO3 ---> 3 Cu(NO3)2 + 2 NO + 4 H2O

With the stoichiometry defined above and using the appropiate molecular weights, we can calculate how much copper (II) nitrate should be produced from 2.25 g of Cu:

2.25 g Cu x 562.7 g Cu(NO3)2 / 190 g Cu = 6.64 g Cu(NO3)2 should be produced.

But, only 3.35 g of Cu(NO3)2 are present and so the %yield is:

3.35/6.64 x 100 = 50.4%

7. You didn't include in the image what the reaction in the laboratory will be so I can't say what are these liquids.

8. The limiting reagent in a reaction is the one that, being in smaller quantities than the other reagents, will stop further reacting once it is completely depleted. Stoichiometric calculations are made based on the limiting reagent.

9. In any reaction the maximum percent yield is 100%, save when in the measurements impurities are considered, in which case the % yield could exceed 100%.

10. Decantation is a process for the separation of mixtures, by removing a layer of liquid, generally one from which a precipitate has settled. Filtration is any of various mechanical, physical or biological operations that separate solids from fluids (liquids or gases) by interposing a medium through which only the fluid can pass. The fluid that passes through is called the filtrate.

11. Cu(OH)2(s)-------> CuO(s) + H2O(l). The reaction is already balanced and doesn't need additional coefficients.

12. H2SO4(aq) + CuO(s) -------> CuSO4(s) + H2O(l). The reaction is also already balanced.

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