Practice Question

[Shaleena 3C]

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

Can someone help me work this out? :)

[Ivy Nguyen 3I]

Hi!
I broke this question down into 3 parts.
1. Find the unknown metal "M" by subtracting the known portion ((OH)2) from the total mass (74.10 g/mol) which would then give you the remaining mass of the unknown metal. From that mass, you can match it to a metal on the periodic table and from what I remember, I believe it would be calcium (about 40 g/mol)
2. You now know that the unknown metal is Ca and the next part of the question is asking for the sulfide of this metal. You would then have CaS
3. Solve for the molar mass of CaS

[Ellie Fox 2K]

I agree with the post above, the way I did it was using the molar mass of the whole compound M(OH)2, subtract the molar mass of (OH)2 from this number. This will give you 74.1-34.016 which equals 40.01. This is the exact molar mass of Ca which makes that your mystery metal. Then just find molar mass of CaS.

[Raizel Ferrer 1H]

As said in the previous posts above, you would first subtract the mass of (OH)^2 from 74.10 g/mol since it is the known mass. Then, find the the metal in the periodic table that matches the mass calculated from the previous step. Finally, since you are trying to find the molar mass of MS, add sulfur's molar mass to the mass calculated in the previous steps. Hope this helps!