Copper, a metal known since ancient times, exists in two stable isotopic forms, 6329Cu (69.09%) and 6529Cu (30.91%). Their atomic masses are 62.93 amu and 64.9278 amu respectively. Calculate the average atomic mass of copper.

Wt. Avg. Atomic Weight => 63.35457 amu

Explanation:

Given              Isotopic             %Abundance     fractional          Wt Avg

                  At. Mass (amu)                                  abundance      contribution                    

Cu-63              62.93                      69.09              0.6909            43.4783

Cu-65              64.9278                  20.0668        0.200668        20.0668

Wt Average of all isotopes = ∑Wt Avg Contributions

=  43.4783 amu + 20.0668 amu = 63.35457 amu

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2