E15 Homework Problem

[Mallika Chimpiri 3K]

" 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? "
How would you go about this problem?

[Sidharth D 1E]

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 S^2-)

CaS

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

[005384106]

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

[KaleenaJezycki_1I]

To go about this problem:
1. Look at the given information M(OH)2 = 74.10 g/mol
2. M is a variable that currently is unspecified (it is just some random metal) BUT you know the elements O and H, therefore find the molar mass for (OH)2
= 34.01 g/mol
3. Now that you know the molar mass of (OH)2, you can subtract that value from the given molar mass to solve for M.
74.10-34.01= 40.09g/mol (the M value)
4. Compute the molar mass of sulfide (S)= 32.06 g/mol
5. add the mass of M+ mass of s
(40.09 + 32.06)= 72.15 g/mol which is the new molar mass of MS