Question E.15 [ENDORSED]

Colette Ussery 3L
Posts: 19
Joined: Wed Sep 21, 2016 2:58 pm

Question E.15

E.15 (on page F50) The molar mass of the metal hydroxide M(OH)2 is 74.01 g*mol^-1. What is the molar mass of chloride in this metal?
1) How are we supposed to find the molar mass of chloride in this metal if chloride isn't even included in its molecular formula?
2) In the molecular formula of the metal, M(OH)2, what is M? I have found no element on the periodic table who has the abbreviation M.
3) In the solutions manual the solution to E.15 reads:
The molar mass of the metal=74.10 g*mol^-1 - 34.02 g*mol^-1 = 40.08 g*mol-1 (Ca): The molar mass of calcium sulfide (CaS)= 72.15 g*mol.

How did they get 34.02 g*mol^-1 ? I looked on the periodic table and found no element with that molar mass. Also, why did they find the molar mass of CaS, when the question asked for the molar mass of chloride?

Abigail_Low_1A
Posts: 30
Joined: Sat Sep 24, 2016 3:01 am

Re: Question E.15  [ENDORSED]

1) You're not looking for the molar mass of chlorine (or chloride) in the molecular formula of M(OH)2. You're suppose to find out what the metal M is, and then determine the molar mass of MCl. For example, if you do the work and find out that the metal is sodium, then you would be looking for the molar mass of NaCl. [The question is actually asking for the sulfide, but it's the same concept]
2) M is just a variable, you're supposed to do the work to find what metal M stands for.
3) 34.02 g/mol is the molar mass of (OH)2 [2*(16+1.008)]. The question does actually ask for the sulfide of the element and not the chloride! #16 asks for the chloride haha.

Colette Ussery 3L
Posts: 19
Joined: Wed Sep 21, 2016 2:58 pm

Ok thank you!