Problem E.15 Confusion [ENDORSED]

[Reilly Charles 3I]

The textbook uses the notation M(OH)₂ as the formula for a metal hydroxide. I was just wondering if the M represented the fact that it is a metal or something else like molarity (the molar mass is listed right after). Also, it asks for the molar mass of the sulfide of this metal, so would the M possibly be a variable for that?

[Kevin Ru 1D]

I believe the M is indeed a variable that represents the unknown metal in the compound. Since you can calculate the molar mass of (OH)2, you can then subtract that from the given molar mass of the compound to find out the molar mass of "M". After checking the periodic table you will discover that "M" is Ca. To answer the question, you would calculate the molar mass of CaS as that is the sulfide of "M". Hope that helps!