## How to do E15

RKopeikin_3L
Posts: 7
Joined: Fri Aug 30, 2019 12:17 am

### How to do E15

E15 says the molar mass of the metal hydroxide M(OH2) is 74.10 g/mol. What is the molar mass of the sulfide of this metal?

I have no idea how to solve this problem, could anyone explain it to me please?

Abigail Menchaca_1H
Posts: 104
Joined: Sat Sep 07, 2019 12:19 am

### Re: How to do E15

Since you don't know what the metal is in this metal hydroxide, you will have to find that first. You want to subtract the hydroxide from the metal 74.10 - (2x1.008 + 2x15.999)= 39.94g/mol. On the periodic table, that mass is closest to Calcium. So your metal is Calcium! Now you want to add the molar mass of calcium to the mass of sulfide (32.05g/mol)- 40.078+32.05=72.13g.
Last edited by Abigail Menchaca_1H on Wed Oct 02, 2019 12:35 am, edited 1 time in total.

Posts: 53
Joined: Thu Jul 25, 2019 12:17 am

### Re: How to do E15

In the last sentence, I think you meant to say add the molar mass of Calcium (39.94g/mol) to the molar mass of a Sulfide ion (32.05 g/mol) in order to find the solution.

Chanel D_4E
Posts: 57
Joined: Wed Sep 11, 2019 12:17 am

### Re: How to do E15

You are trying to find the molar mass of M so essentially what does M=?
1) The molar mass of (OH)2 is 34.02 g/mol
2)Molar mass of metal (M) = 74.10 g/mol - 34.02 g/mol
= 40.08 g*mol^-1
When you look at the periodic table the molar mass matches the element Ca
3) Now find the molar mass of Calcium Sulfide or CaS to answer the question.
Molar mass of Ca= 40.08 g/mol
Molar mass of S= 32.06 g/mol
Molar mass of CaS = 40.08 g/mol + 32.06 g/mol
= 72.14 g/mol

Ellis Song 4I
Posts: 102
Joined: Thu Jul 11, 2019 12:17 am

### Re: How to do E15

First you find the molar mass of (OH)2 by adding together the molar mass of oxygen and hydrogen then multiplying by 2. Then you subtract that from the given molar mass, 74.10, to find the molar mass of the metal. The number you get is 40.08 g/mol which is the molar mass of Calcium - you must refer to your periodic table to figure this out. Because the question is asking for the sulfide of this metal, you simply take the molar mass of Calcium and add it to the molar mass of Sulfur and you should get 72.15 g/mol.