Question

Question #049d8

Answer 1

15.5 grams

Explanation:

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.