Answer:
Atomic mass of E is 15.95 g/mol
Explanation:
To solve this we must begin with this knowledge:
1 mol of Al₂E₃ contains 2 moles of Al and 3 moles of E
The percentages shows the mass of elements in 100 g of salt, so we must think this rule of three.
2 moles of Al = 2 mol . 26.98 g/mol → 53.96 g (the mass of Al, in 1 mol of Al₂E₃)
If 52.99 g of Al, are contained in 100 g of salt
53.96 g of Al, would be contained in (53.96 . 100) / 52.99 = 101.8 g of salt.
This is the molar mass of the salt, 101.8 g/mol. Therefore, we can think another rule of three.
In 100 g of salt we have 47.01 g of E
In 101.8 g of salt we would have (101.8 g .47.01g) / 100g = 47.87 g of E
This number, 47.87 g represents the amount of 3 moles of E, so if we want to know the molar mass, we should do this g/mol
47.87 g / 3mol = 15.95 g/mol
We can make a verification of this. Imagine that we have the molar mass ( 101.8 g/mol ) and the percent of composition so we have to find out the molecular formula.
We divide the percent between the molar mass of each element
52.99 g /26.98 = 1.96
47.01 g / 15.95 = 2.95
Now we divide between the less value of both
1.96 / 1.96 = 1
2.95 / 1.96 = 1.50
As we must have integer numbers in the formula we multiply x2, so the formula will be correctly Al₂E₃
