Question

A metal M is converted to the metal sulfate M2(SO4)3. then a soultion of the metal sulfate was treated with calcium chloride to give calcium sulfate perciptate.If 1.2 g of the metal gave 5.451 g calcium sulfate what is the identity of metal M?
M2(SO4)3(aq)+3CaCl2(aq) ----->
2MCl3(aq)+3CaSO4(s)

Answer 1

1) From the chemical equation you obtaing the theoretical molar ratios:

2 mol of M : 3 mol of CaSO4

2) Convert 5.451 g of CaSO4 into number of moles

number of moles = mass in grams / molar mass

molar mass 0f CaSO4 = 136.14g/mol

=> number of moles of CaSO4 = 5.451 g / 136.14 g/mol = 0.0400 mol

3) Make a proportion with the unknown, 0.0400 mol and the theoretical molar ratio:

x / 0.0400 mol of CaSO4 = 2 mol of M / 3 mol of CaSO4

=> x = 0.400 * 2 / 3 mol of M = 0.02667 mol of M

4) Use the mass of 1.2 g and the number of moles to obtain the molar mass of M

molar mass = mass in grams / number of moles

=> molar mass = 1.2 g / 0.02667 moles = 45 g/mol

5) Use a periodic table to find the molar masses of different metals.

Scandium atomic mass is 45 g/mol, so the metal is Scandium.

Answer: Scandium