[ygao85]

Ok i know how to do these kind of problem. There is just this one that i can't figure out:


"The 1st substance to act as a superconductor at a temp above that of liquid nitrogen(77K) was discovered in 1987. The approx. formula of this substance is YBa₂Cu₃O₇. Calculate the % composition by mass if this material."

The molar weight of the molecule is not give and we don't know what Y is. How do we start this kind of problem? Thank you.

[savoy7]

Y = Yttrium check the periodic table in the menu on the left side of this page

% composition by mass

1)  need unit formula - given
2)  determine molar mass for each individual element and for the entire unit formula
3)  determine % for each element by dividing each element's molar mass by the total (of course multiple by 100% to get %).

do the work and post - someone will check it for you

by the way - nice picture of it
http://www.kreysite.com/asc/ybco.html