IIT JEE , AIEEE Forum - Chemistry , Physical Chemistry

divalli_oct07

a compound which contains 1 atom of X and 2 atoms of Y for each 3 atoms of Z is made by mixing 5.00g of X , 1.15*10 ²³atoms of Y and 0.03 mole Z atoms. given that only 4.40 g of compound results. calculate the atomic wt of Y if the atomic wt of X and Z are 60 , 80 amu.

cooldude

no. of moles of X=5/60=1/12.

Y=1/4

Z=3/100.

since X,Y and Z must be in 1:2:3 ratio,the limiting reagent is Z

and thus 1/100 moles of the compound is formed which is given as 4.4 gms.

hence mol wt of compund is 4.4 X100=440.

let the atomic wt of Y be some m.

then,

1X60+2Xm+3X80=440

we get atomic wt of Y,m=70.

titun

No. of gm atoms of X taken initially = 5 / 60 = 0.083 ( approx. )
No. of gm atoms of Y taken initially = 1.15 x 10 ^23 /(6.023x10^23) = 0.019 (approx)
No. of gm atoms of Z taken initially = 0.03

As given in the problem, 1 atom of X and 2 atoms of Y are required for each 3 atoms of Z.

So, all the gm atoms of Z will be utilized in the reaction but X and Y will be left as residue.

Since, 0.03 gm atoms of Z participates in the reaction, 0.02 moles of Y & 0.01 moles of X are used in the reaction.

Wt. of utilized moles of X in the reaction = 0.01 x 60 = 0.6 gm
Wt. of utilized moles of Z in the reaction = 0.03 x 80 = 2.4 gm

So, the rest of the wt. of the compound i.e (4.4 - 2.4 - 0.6) or 1.4 gm must be due to the 0..02 gm atoms of Y

Wt. of 0.02 gm atoms of Y is 1.4 gm
Hence, wt. of 1 gm atom of Y is 1.4 / 0.02 gm i.e 70 gm
Therefore, 1 atom of Y weighs 70/(6.023x10^23) gm = 70 amu

Therefore, atomic weight of Y is 70 amu

Cheers !!

Ask & Discuss Questions with Community & Experts