Astudent was asked to determine the densities of the four metals listed. the student was asked to determine the density of an unknown metallic substance. the metallic substance is an alloy. this particular alloy is a 50/50 mixture of two metals listed in the table. the student found the density of the alloy to be 9.32 g/cm3. according to the density, what two metals make up the alloy? a) lead and gold b) copper and tin c) copper and gold d) tin and lead

D is correct

Explanation:

because

we know that

density of lead is 11.36 g/cm3

and

density of tin is 7.31 g/cm3

so..

density of alloy by mixing 50/50

=(11.36+7.31)/2 g/cm3

=18.67/2 g/cm3

=9.33 g/cm3

n2(g) + 3h2-> 2nh3(g)   this is the balanced equation

note the mole ratio between n2, h2 and nh3.   it is 1 : 3 : 2   this will be important.

moles n2 present = 28.0 g n2 x 1 mole n2/28 g = 1 mole n2 present

moles h2 present = 25.0 g h2 x 1 mole h2/2 g = 12.5 moles h2 present

based on mole ratio, n2 is limiting in this situation because there is more than enough h2 but not enough n2.

moles nh3 that can be produced = 1 mole n2 x 2 moles nh3/mole n2 = 2 moles nh3 can be produced

grams of nh3 that can be produced = 2 moles nh3 x 17 g/mole = 34 grams of nh3 can be produced

note:   the key to this problem is recognizing that n2 is limiting, and therefore limits how much nh3 can be produced.