Question

Question #d422b

Answer 1

The equivalent mass is 12.0 g meaning this metal is magnesium. Details follow...

Explanation:

First, we need to determine the number of moles of acid in 100 mL of 0.50 M HCl:

Since Moles of solute = Concentration of solution x Volume in litres

Moles = `0.500 ("mol"/L) xx 0.200 L = 0.100` mol

To get the equivalent weight of the metal, we assume the following reaction is a one-to-one ratio (which is the same as saying that metal M releases one electron as it is oxidized by the acid):

`M + HCl rarr M^+ + 1/2H_2 + Cl^-`

Since the amount of acid was 0.100 mol, the 1.2 g of M must be 0.100 mol as well.

Since Moles = mass / molar mass

it follows that molar mass = mass / moles

So, molar mass (actually the equivalent mass in this case) is

`"mass" -: "moles" = 1.2 g -: 0.10 "mol" = 12 g`

Note that this means the element is magnesium, because Mg would release two electrons in the reaction, giving it an equivalent weight of 12.1g. It would react this way with HCl:

`Mg + 2HCl rarr Mg^(2+) + H_2 + 2Cl^-`

meaning the equivalent weight of 12 is multiplied by two to get the actual molar mass of 24 g.