Question #049d8

1 Answer
Oct 8, 2017

15.5 grams


The ratio of x to y is 3:4. Since we know how many atoms of y there are, we can set up a proportion:

#3/4 * x/(3.2*10^23 " atoms of y")#

#x = ((3.2*10^23 " atoms of y") * 3) / 4 = 2.4 * 10^23 " atoms of x"#

Next, we convert the value we just found into moles:

#2.4 * 10^23 " atoms of x" * (1 " mole")/(6.022 * 10^23 " atoms") = 0.3985 " moles of x"#

We know how many grams of x there are, so with the help of a little dimensional analysis, we can find the amount of grams

#(18.5 " grams of x")/(0.3985 " moles of x")= 46.424# #"grams"/"mole"#

Next, we need to divide this value by three, since there are three atoms of x per every four atoms of y. In another words, the molecular formula given looks something like this: #N_xO_y#. Disregard, the N and O in that molecular formula - it's merely an example. We found the molar mass of #N_x# but we need the molar mass of #N#.

#(46.424 "grams"/"mole")/ 3" = 15.5# #"grams"/"mole"#

The element closest to that value of atomic weight is Oxygen, which has a molar mass of 15.9994 grams.