5. 1.250 g of an alloy which is 90.00 % Ag and 10.00 % Cu is reacted with nitric acid producing AgNO3 and Cu(NO3)2 dissolved in solution. To the solution of the nitrate compounds is added a piece of copper wire that reacts only with the AgNO3 in solution to precipitate all of the silver, and produce additional Cu(NO3)2 (aq) . (The equation for this single-replacement reaction is: AgNO3(aq) + Cu(s)  Cu(NO3)2(aq) + 2 Ag(s) ) The resulting solution containing all of the Cu(NO3)2 produced by the above processes is treated with excess zinc to precipitate the entire amount of copper (ll) ion present. ( The equation for this step is Cu(NO3)2(aq) + Zn(s)  Zn(NO3)2(aq) + Cu(s) ) What mass of copper will be precipitated?

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Explanation:

According to the question Copper is obtained from  the original alloy and the copper wire used to displace the silver.  

So,

Mass of the copper from the original alloy: (10.00 % * 1.250 g) =  0.125 g

We now need to obtain the mass of the copper from the wire, then we consider how much silver is precipitated:

Mass of silver in the alloy; 90.00 % * 1.250 g = 1.125 g

So,

Amount of silver precipitated =

1.125 / 107.9 = 0.01043 mole

From the reaction equation, it takes two moles of silver to displace one mole of copper.

Hence, the amount of copper from the wire is:  0.01043 / 2 = 0.005213 mol

And a mass of  0.005213(63.55) = 0.3313 g

Total mass of copper=  0.125 + 0.3313 = 0.456 g

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."

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