Page 1 of 1

### E15 Homework Problem

Posted: Sun Oct 06, 2019 7:25 pm
" The molar mass of the metal hydroxide M(OH)2 is 74.10 g*mol^-1. What is the molar mass of the chloride of this metal? "

### Re: E15 Homework Problem

Posted: Sun Oct 06, 2019 7:48 pm
1st, I think the question is asking for the sulfide of the metal, not chloride (you mixed up E15 with E16)

Step 1: Calculate the molar mass of the known parts of that compound [ the (OH)2 ]

molar mass of (OH)2 is 34.02 g/mol

Step 2: Subtract that known molar mass from the total to get the molar mass of the unknown metal

Metal molar mass: 74.10 g/mol - 34.02 g/mol = 40.08 g/mol

Step 3: Find the element, using the periodic table, which is closest to that molar mass: (Calcium)

Step 4: Write the molecular formula of this metal when combined with sulfur: (Ca2+ and S2-)

CaS

Step 5: Calculate the molar mass of that compound: 72.14 g/mol

### Re: E15 Homework Problem

Posted: Sun Oct 06, 2019 8:00 pm
First, you need to find which metal element is represented by M in the given compound. You can do this by subtracting the mass of the hydrogen and the oxygens from the molar mass given.
74.10 - ( 2x1.008+2x15.999) =39.94 g/mol
Now using the periodic table you will be able to see that the element with an atomic mass closest to 39.94 is Calcium (40.078)
Next find the molar mass of chloride using the calcium metal.
40.078+35.453=75.53

### Re: E15 Homework Problem

Posted: Wed Oct 09, 2019 6:16 pm