Two elements X and Y combine to form two compounds XY2 and Y3X2. 0.1mol of XY2 weighs 10g and 0.05mol of Y3X2 weighs 9g. Calculate the atomic masses of X and Y.
Answer & explanation
Correct answer: option 3
The correct answer is option 3. X=40, Y=30
\(\text{Suppose atomic masses of X and Y are x and y respectively.}\)
\(\text{Molar Mass of }XY_2\text{ = }x+2y\)
\(\text{But 0.1mol of }XY_2 weighs \text{ = 10g}\)
∴ \(\text{Molar Mass of }XY_2\text{ = }100\)
∴ \(\text{x + 2y = 100 -------------------- (i)}\)
\(\text{Molar Mass of }X_3Y_2\text{ = }3x+2y\)
\(\text{But 0.05mol of }X_3Y_2 weighs \text{ = 9g}\)
∴ \(\text{Molar Mass of }X_3Y_2\text{ = }\frac{9}{0.05}\text{ = }180g\)
∴ \(\text{3x + 2y = 180 -------------------- (ii)}\)
\(\text{Subtracting equation (i) from equation (ii), we get}\)
\(\text{2x=80 or, x = 40}\)
\(\text{Substituting in equation (i), we get }\)
\(\text{40 + 2y = 100 or, 2y = 60 or, y = 30}\)