Question

I am having trouble calculating the molecular weight after getting the percent of M which is 46.62% from this question..The chloride of an unknown metal is believed to have the formula MCl3. A 2.395 g sample of the compound is found to contain 3.606 x 10^-2 mol of Cl. Find the atomic mass of M.

Answer 1

3.606 * 10^-2 mol of Cl...that means there exist (3.606 * 10^-2 )/3 = 1.202 * 10^-2 mol of M.
In order to figure out the # of grams of Cl in the compound.
the atomic mass of Cl is 35.45 grams. so for one mole of Cl, it weighs 35.45 grams
3.606 * 10^-2 mol x (35.45 g / 1 mol) = 1.278 g Cl
Since the total weight of the compound (M + Cl) = 2.395 g and the weight of Cl is 1.278 then the weight of M is equal to 2.395 - 1.278 = 1.117 g M

now...the units for atomic mass is g/mol

we know that 1.117 g of M and 1.202 * 10^-2 mol
1.117 / 1.202*10^-2 = 92.93 g /mol