Depending on the reaction conditions, elements x and y react by a weight ratio of either 1 part of x and 1.982 parts of y, or 1 part of x and 5.946 parts of y, forming two different compounds. which of the following pairs of substances is inconsistent with the above data?

(a) x3 y and x3y3
(b) x3y2 and x3y6
(c) xy and x3y
(d) xy and x3y3
(e) x3y2 and xy2

(c) and (d)

Explanation:

The law of definite proportions states that elements in compounds always have a fixed atomic ratio independent of any conditions.

In the context of this problem, we only know the mass ratio of X to Y, but we don't know the molar ratio, so we cannot derive the empirical formula.

However, we notice that in the second compound, mass of Y increased by a fraction of:

Since mass is directly proportional to moles, in the second compound we should have three times larger number of atoms of Y for the same number of atoms of X (1 part in each case lets us assume this).

a. Notice that X is kept constant and Y increases by a factor of 3, so it's consistent.

b. Similarly to (a), X is kept constant and Y increases by a factor of 3, so it's consistent.

c. Here, Y is kept constant. X increases by a factor of 3. This is inconsistent with the data, since if we start with , then we'd have as our second pair, since we should have three times greater number of Y atoms in the second structure.

d. The molar ratio here in each pair is the same, XY is the empirical formula for . This means it's inconsistent, as here both formulas have the same ratio of X to Y.

e. This is consistent, since for a constant Y, in the second structure we should have one third of X atoms to obtain the 3 : 1 ratio.

a