college chemistry 1

Question

a scientist is trying to discover information about an unkown metal in a compound. the formula for the compound is believed to be XBr3 where X is the unknown metal. The Scientist that determined that a 4.725g sample of this compound contains 4.750 x 10^-2 mol Br.

Calculate the atomic mass of the unknown metal, X

What is the identity of the metal

Answer 1

As we know the number of moles of Br, we can determine the mass of the Br by multiplying the moles by the atomic mass of Br.

4.75 x 10^-2 x 79.904 = 3.795 g Br. The mass of the metal is 4.725g - 3.795g = 0.9300 g metal.

As there are 3 atoms of Br, and the number of moles is given as 4.75 x 10^-2 moles, the number of moles of the metal is 4.75 x 10^-2 / 3 = 0.01583 moles of X.

Knowing the moles of X and its mass, we can calculate the atomic mass by dividing the grams of X by the number of moles of X.

0.9300 gX / 0.01583 moles X = 58.75 g/mole. This atomic mass corresponds most closely to Nickel.