An ionic compound has the following composition (by mass): Mg, 10.9%; Cl, 31.8%; O, 57.3%. What is the formula and name of this compound?

You do this the same way you work the CHFO problem. Post your work if you get stuck.

To determine the formula and name of this compound, we need to first calculate the empirical formula. The empirical formula represents the simplest ratio of elements in a compound.

Step 1: Convert the percentages to grams.
Given:
Mg: 10.9% Cl: 31.8% O: 57.3%

To convert the percentages to grams, assume we have 100g of the compound.
Mg: (10.9/100) x 100g = 10.9g
Cl: (31.8/100) x 100g = 31.8g
O: (57.3/100) x 100g = 57.3g

Step 2: Determine the number of moles for each element.
We can use the molar mass to convert the grams to moles.

Mg:
Molar mass of Mg = 24.31 g/mol
Number of moles of Mg = 10.9g / 24.31 g/mol = 0.449 mol

Cl:
Molar mass of Cl = 35.45 g/mol
Number of moles of Cl = 31.8g / 35.45 g/mol = 0.897 mol

O:
Molar mass of O = 16.00 g/mol
Number of moles of O = 57.3g / 16.00 g/mol = 3.57 mol

Step 3: Find the simplest ratio of elements.
Divide the number of moles of each element by the smallest number of moles to find the ratio.

Mg: 0.449 mol / 0.449 mol = 1
Cl: 0.897 mol / 0.449 mol = 2
O: 3.57 mol / 0.449 mol = 8

Therefore, the simplest ratio is 1:2:8, and the empirical formula is MgCl2O8.

Step 4: Determine the formula and name of the compound.
The empirical formula MgCl2O8 can be simplified. Dividing all subscripts by 2 would give us the simplest whole numbers.

Simplified empirical formula: MgClO4

Naming the compound:
The name of the compound with the empirical formula MgClO4 is magnesium perchlorate.