Question

Preparation of CuCl

Reactions: 1) Cu(S) + 4HNO3(aq) -> Cu(NO3)2(aq) + 2NO2(g) + 2H2O(l) 2) 2HNO3(aq) + Na2CO3(s) -> H2O(l) + CO2(g) + 2NaNO3(aq) 3)Cu(NO3)2(aq) + Na2CO3(s) -> CuCO3(s) + 2NANO3(aq) 4)CuCO3(s) + 2HCL(aq) -> CuCl2(aq) + H2O(l) + CO2(g) 5)CuCl2(aq) + Cu(s) -> 2CuCl(s)

Weight of copper: 1.023g

Volume of Added Nitric Acid: 5.5 mL

Total weight of added Sodium Carbonate: 3.85g

Weight of Watch Glass and filter paper: 51.533g

Weight of Watch Glass, Filter Paper and CuCl Precipitate: 53.524

Experimantal Yield of CuCl: 1.991g

Theoretical Yield of CuCl: 3.187g CuCl

Percent Yield of CuCl: 62.47%

1) Based on the amounts of copper metal and nitric acid you used in the 1st reaction, calculate the number of moles of HNO₃ there are in excess. Concentrated nitric acid has a concentration of 15.8 M.

2. Using the moles of HNO₃ you calculated and the moles of Cu(NO₃)₂ produced from the 1st reaction, calculate the total mass of sodium carbonate needed for the second and third reactions. Did you add enough sodium carbonate in the experiment?

3. What observation suggests that copper was added in excess during the last reaction?

4) Why might a student obtain a percent yield less than 100% for this preparation?

5) Copper metal reacts with dilute nitric acid by the following reaction.

3Cu(s)+ 8HNO₃(aq) ->3Cu(NO₃)₂(aq) + 2NO(g) + 4H₂O(l)

If this reaction took place rather than the 1st reaction, would your yield of CuCl be affected assuming you started with the same amount of copper metal? Explain your answer.

6) Could we use HCl to dissolve the copper metal instead of nitric acid in the first reaction? Explain your answer.

7) Given the following three sequential reactions:

a) N₂(g) + 3H₂(g) -> 2NH₃(g)

b) 4NH₃(g) + 5O₂(g) -> 4NO(g) + 6H₂O(g)

3) 2NO(g) + O₂(g) -> 2NO₂(g)

What mass of hydrogen gas is needed to produce 165.0 kg of nitrogen dioxide?

Answer 1

4) You can have experimentally over 100% easily, I have it all the time in my lab. This happens mostly because it is not dry, if there are still extraneous solvents when working with microscale reactions, it can really mess up your yields. essentially if it's over 100% that means you have impurities.

to have less than 100% (which is probably the most common). Every time you transfer a component or reaction to another container, you lose some of your compound. A basic rule of thumb is to minimize transfers.
Another way to have less than 100% is due to equilibrium. If you are just running a straightup reaction, it'll be pretty much impossible to get 100%. This is because you will reach the equilibrium point of the reaction. You have to modify the equilibrium to get 100%.
Another way to get less than 100% is by stopping the reaction before it has completely reacted.

And of course the catch-all: Human error. Say you can't read a graduated cylinder right, or forgot to tare the scale before you used it.

6)When you are using Hydrochloric Acid (aka: HCl), it will "attack" nearly anything above hydrogen, including, Lead, Aluminum, Magnesium, Tin, Zinc, etc. (Lead is a bit of a challenge for HCl because Lead Chloride is insoluble, and can form a protective coat that stops the reaction from occurring. It does actually react on the surface and if you add some heat to the reaction, it can push it even further.) But, as Copper is below Hydrogen, it is not attacked by HCl...

With Nitric Acid (aka: HNO3), in dilute form, the reaction is the same as with HCl... However, if you are using concentrated HNO3, the nitrate portion of the acid IS able to attack the Copper... This, because the nitrate is a powerful oxidizing agent when in high concentration. The nitrate portion is reduced to NO2 gas and the metal is oxidized. This reaction allows concentrated nitric acid to also attack metals that are "below" hydrogen (to some extent). Mercury, copper, and silver are all readily attacked by this reaction...

5)