During the Reactions of Copper experiment, aqueous ammonia is added to a CuClz(a

Question

During the Reactions of Copper experiment, aqueous ammonia is added to a CuClz(ag). A precipitate forms and then dissolves. Why does this happen 10. solution of A The ammonia solution is basic, so an insoluble hydroxide forms first. Then reacts with copper ions to dissolve them. the ammonia becomes acidic and the solid copper forms Cu? (aq) as it generates reacts with ammonia for form finely divided copper metal. Then the solution chloride ions react with the ammonia to form insoluble ammonium chloride which then reacts with the copper to form the deep blue copper D. The -ammonia complex. ammonia reacts with the water so that CuCl(s) precipitates. Then the chloride lons react with the ammonium ions to form soluble ammonium chloride. 11. We identified the end point in the Titration of Antacids experiment was when the color of the solution changed from red to yellow. This change occurred because a slight excess of acid was added after the equivalence point. B. a slight excess of base was added after the equivalence point. C A. it signaled that the reaction mixture had cooled to room temperature after being boled. D. the antacid had completely neutralized the NaOH(aq) added from the buret. E. the antacid had completely neutralized the HCl(aq) added via the pipet r experiment Assume that when a student was conducting the Apparent Molar Mass of A a small amount of air leaked back into the flask through the tightened screw clamp and the student was unaware that this had happened. How would this have affected her calculated value for the apparent molar mass of the air? -12. A. It would not have had any effect since we had to allow the flask to cool before reweighing it B. It would have led to an increase in the calculated value because it would have cooled off the air in the flask and she would have used too large a value for T It would have It would have led to a decrease in the calculated value because the flask would now weigh It would have led to an increase in the calculated value because the flask would now weigh led to an increase in the calculated value because the flask would now weigh C. D. E. more than it should and give too large a change in the mass of air in the flask. more than it should and give too small a change in the mass of air in the flask more than it should and give too small a change in mass of air in the flask. 13. In order to perform the Solution Calorimetry and Hess's Law (Enthalpy of Formation) experiment, what assumption(s) was/were it necessary to make? The specific heat of the reaction system (solution) is essentially the same as water. A. B. Absolutely no heat enters or leaves the calorimeter during the experiment C. The chemical and physical processes being studied are neither endothermic nor exothern D. The maximum and minimum temperatures read on the thermometer accurately reflect the corresponding temperatures reached by the reaction system.

Explanation / Answer

CuCl2 reacts with ammonia as follows

CuCl2 + 4NH3 [Cu(NH3)4]Cl2

The above reaction clearly shows that

the precipitate first forms then dissolves because the copper ions react with ammonia to form insoluble ammonium chloride which then react to form the deep blue copper ammonia complex

Hence option (c) is correct.

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