Question E 15

[Brian Chhoy 4I]

The question states that the molar mass of the metal hydroxide M(OH)2 is 74.10 g/mol and asks to calculate the molar mass of the sulfide of the metal. I'm assuming that the M is a variable for a certain metal with a +2 charge. Is the question simply asking for the molar mass of MS, by subtracting the molar mass of the two hydroxide atoms from the molar mass of the metal hydroxide, and then adding the calculated mass of the metal to the molar mass of sulfur? 74.10 - 34.016 = 40.084 + 32.07 = 72.154 g/mol ?

[katherinemurk 2B]

When you subtract the molar mass of the metal of the two hydroxide atoms from the molar mass of the metal hydroxide, you get a molar mass of 40.084. And the metal matching this molar mass is calcium (40.078) so now you take find the molar mass of calcium sulfide!

[Hannah Faris 1C]

Yeah, that's all correct. As you have done, you subtract 2 times the molar mass of OH from the given molar mass, and then add the molar mass of sulfur to find the total molar mass it as a sulfide. Since the oxidation numbers check out (unknown metal is +2, sulfur is -2) you only need to use one sulfur. You got it!

work:
74.10g/mol-2*(17.008g/mol)= 40.08g/mol as molar mass of M
then add the molar mass of sulfur 32.06 to get 72.14 g/mol