Molarity

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Jessica Esparza 2H
Posts: 130
Joined: Wed Sep 18, 2019 12:15 am

Molarity

Postby Jessica Esparza 2H » Wed Oct 02, 2019 6:53 pm

What would be the proper steps to answer the following question? The molar mass of the metal hydroxide M(OH)2 is 74.10g per mole. what is the molar mass of the sulfide of this metal?

claribel charway 1I
Posts: 55
Joined: Wed Sep 11, 2019 12:15 am

Re: Molarity

Postby claribel charway 1I » Wed Oct 02, 2019 7:04 pm

First you need to subtract the mass of (OH)x2 from the molar mass of the metal. When subtracting you find out the unknown metal is calcium.
74.10 - 34.02 = 40.08
Next, add the mass of Sulfur to the remaining amount. This is adding the masses of Calcium and Sulfur to create calcium sulfide.
40.08 + 32.07 = 72.15

Ryan Yee 1J
Posts: 101
Joined: Sat Aug 17, 2019 12:16 am

Re: Molarity

Postby Ryan Yee 1J » Wed Oct 02, 2019 7:09 pm

So the metal hydroxide just basically means that the metal 'M' is combined with two hydroxide ions (OH-)2. You want to find the sulfide of this ion, or what the molar mass would be when combined with an S2-. Taking away the molar mass of hydroxide would mean subtracting 2(17.01) from the original molar mass to get 40.08, which is about the mass of calcium. Calcium combines with sulfur to form calcium sulfide (CaS) and would have a molar mass of 72.14.

Jarrett Peyrefitte 2K
Posts: 102
Joined: Sat Aug 24, 2019 12:16 am

Re: Molarity

Postby Jarrett Peyrefitte 2K » Wed Oct 02, 2019 7:14 pm

The first step is to find out what the unknown metal is. To do this you must take the given molar mass and subtract it from the mass of the two hydrogens and oxygens.

74.10 - ( 2x1.008+2x15.999) =39.94 g/mol

Then you must find this molar mass on your periodic table, and this molar mass comes out to Calcium (Ca).

Then solve for calcium sulfide

40.078+32.05=72.13 g/mol

Jessica Esparza 2H
Posts: 130
Joined: Wed Sep 18, 2019 12:15 am

Re: Molarity

Postby Jessica Esparza 2H » Wed Oct 02, 2019 9:42 pm

Thank you, everyone, for your help!


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