Question

A sample of 0.351 mol of a metal M reacts completely with excess fluorine to form 27.4 g of MF2. Identify the metal M.

a. Sr
b. Ca
c. Mg
d. Ar
e. K

Answer 1

The metal M in the reaction is magnesium (Mg).

Step-by-step explanation:

In order to determine the metal M, we need to first calculate the molar mass of MF2. The molar mass of the compound is 27.4 g/mol. Since the ratio of M to F in MF2 is 1:2, we can subtract the molar mass of two fluorine atoms (2 x 19 g/mol = 38 g/mol) from the molar mass of MF2 to find the molar mass of M. Subtracting 38 g/mol from 27.4 g/mol gives a molar mass of 11.4 g/mol for M. Comparing this value with the molar masses of the given options, we find that the closest match is magnesium (Mg) with a molar mass of 24.3 g/mol. Therefore, the metal M in this reaction is magnesium (option c).

Answer 2

To identify the metal M in the compound MF2, the molar mass of MF2 was calculated using the provided amount of substance (0.351 mol) forming 27.4 g of MF2. The molar mass of Fluorine was subtracted from the molar mass of MF2 to find the molar mass of the metal M, which closely matches that of calcium (Ca).

Step-by-step explanation:

To identify the metal M from the compound MF2, we start by calculating the molar mass of MF2. We have 0.351 mol of the metal, and this amount of substance forms 27.4 g of MF2. From the molecular formula MF2, we know there is 1 atom of M in each formula unit, thus 0.351 mol of M will be present in 0.351 mol of MF2.

First, we calculate the molar mass of MF2:

Molar mass of MF2 = Mass of sample / Number of moles

= 27.4 g / 0.351 mol = 78.06 g/mol (approximately).

We know the molar mass of F (Fluorine) is about 19 g/mol, so for two fluorine atoms, the combined mass would be around 38 g/mol. Subtracting this from the molar mass of MF2 gives us the molar mass of the metal M:

Molar mass of M = Molar mass of MF2 - Mass of 2 F

= 78.06 g/mol - 38 g/mol = 40.06 g/mol (approximately).

Examining the options provided, magnesium (Mg) has an atomic mass close to 24.31 g/mol, which isn't a match. Calcium (Ca), with an atomic mass of about 40.08 g/mol, is a close match. The other options, such as strontium (Sr), argon (Ar), and potassium (K), do not match the calculated molar mass.

Therefore, the metal M in the compound MF2 is most likely calcium (Ca).