Homework E.15 Solutions

[Sisi Li 1F]

On the solution manual (6th edition), there's a Calcium in the equation. Why is that? It is also unclear to me why they subtracted 34.02 g/mol from the total molar mass of the metal.

[Leah farhadi 1F]

We are given that the molar mass of the Metal(M) = 74.10 g.mol^-1

We know using molecular mass that (OH)2 = 34.02 g.mol^-1

So, then we know that the molar mass of the Metal = 74.10 - 34.02 = 40.08

Looking at the periodic table we see that Calcium has an atomic weight of 40.08

Since the question asked for molar mass of Sulfide of this metal (now we know that is is Calcium), we find the molecular mass of CaS

Molar mass of CaS = (40.08 +32.06) = 72.15 g.mol^-1

[D-nice1D]

It took me some time to figure out what to do with the 40.8. Is this(finding the corresponding element) something that will appear often?

[Chem_Mod]

Now that you have seen this type of example it will be easier to recognize what to do.

[Sjeffrey_1C]

Is it assumed we know that the M in M(OH)2 is a sulfide? Or was there some way to determine this?