Molar Mass of a Sulfide of a Metal.

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Kushaal Madadi 2F
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Molar Mass of a Sulfide of a Metal.

Postby Kushaal Madadi 2F » Thu Oct 08, 2020 10:36 am

Fundamentals Section E of the textbook has the following problem:

E.15 The molar mass of the metal hydroxide hydroxide M(OH)2 is 74.10g*mol^-1. What is the molar mass of the sulfide of this metal?

I'm confused as to what some of these terms are referring to. For example, what does metal hydroxide and sulfide of this metal mean? How would you solve this problem?

Chem_Mod
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Re: Molar Mass of a Sulfide of a Metal.

Postby Chem_Mod » Thu Oct 08, 2020 10:41 am

First, find the molar mass of (OH)2. Then, minus this value from the given molar mass (74.10g). This now gives you the molar mass of the metal itself. Using the periodic table, determine which element this molar mass matches with. Finally, combine with S by adding the molar mass of S to find the total mass of the metal sulfide.

Ivy Tan 1E
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Re: Molar Mass of a Sulfide of a Metal.

Postby Ivy Tan 1E » Thu Oct 08, 2020 2:10 pm

Hi!!
When the question says "metal hydroxide", it means that an unknown metal is combined with hydroxide (you have to figure out which metal it is). When it asks for the molar mass for the "sulfide of the metal", you have to calculate the mass of the unknown metal you just found with sulfide. To solve this problem:
1. Find the molar mass of (OH)2.
2. Subtract the molar mass of (OH)2 from 74.10g/mol to find the molar mass of the unknown metal (you should get a mass of 40.084g which tells you that the unknown metal is calcium, based on the molar masses on the periodic table).
3. Find the molar mass of calcium and sulfide (the answer should be 72.14g).
I hope this was helpful!!

Isaac Wen
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Re: Molar Mass of a Sulfide of a Metal.

Postby Isaac Wen » Fri Oct 09, 2020 1:26 am

I was confused on this one as well haha!

I'm pretty sure the M in M(OH)2 just stands for the unknown metal, so essentially you can look at the formula as ?(OH)2. After that, it's like what they said, just find the molar mass of (OH)2 and subtract it from the given molar mass. Then you look at the period table to find out what the unknown metal is!


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