E15 7th Edition

[Mark 1D]

The molar mass of the metal hydroxide M(OH)2 is 74.10 gmol. What is the molar mass of the sulfide of this metal? I understand how to obtain molar mass but how do I identify the sulfide of M(OH)2? Thanks

[Alyssa Bryan 3F]

First you need to figure out what the metal (M) is in the metal hydroxide M(OH)2. Since you have the molar mass of the metal hydroxide you can subtract the molar mass of (OH)2 to find the molar mass of the metal. 74.10-34.02=40.08 g/mol
40.08 is the molar mass of calcium (Ca) so the sulfide would just be CaS (calcium sulfide). From there just add together the molar masses of calcium and sulfur to get the molar mass of CaS.