Problem E.15 in Fundamentals

[Alejandra Reyna 1E]

Problem: The molar mass of the metal hydroxide M(OH)2 is 74.10 g.mol-1. What is the molar mass of the sulfide of this metal?

I am having a lot of trouble approaching the question because I am still very unsure as to what it is asking. I've tried looking at the solution but became more confused. Any clarification would be really helpful!

[Dabin Kang 1B]

Find the molar mass of the unknown element M by subtracting the mass of the hydrogen and the oxygen atoms from the given molar mass of the molecule:

74.10 - 2(1.008 + 15.999) = 40.086 g/mol

This molar mass is the closest to the molar mass of Calcium, so we can assume that M is calcium.

Calcium sulfide is CaS, so the molar mass is 40.078 + 32.065 = 72.143 g/mol

[Alejandra Reyna 1E]

Oh, I get it now! Thank you!

[FCervania 1B]

This was so helpful, thank you! (I was spending like 5 mins looking for some element that had the symbol M and felt I was going a bit crazy lol)