Answer
The atomic weight of the unknown element is 207 g/mol
Explanation:
Given that:
XO2 is the compound
Step 1: we need to find the mole of oxygen
Mole = reacting mass / molar mass
3.20g of oxygen was produced when the compound was heated
reacting mass of oxygen = 3.20g
Mole = 3.20 / 16
Mole of oxygen = 0.2 mole
Oxygen has 2 moles
Element X has 1 mole
We need to find the mole of the unknown element
Let the mole of the unknown element be x
2 ---------- 0.2 mole
1 --------- x mole
Cross multiply
2 * x = 0.2 * 1
2x = 0.2
Divide both sides by 2
2x/2 = 0.2/2
x = 0.1 mole
Therefore, the mole of the unknown element X is 0.1 mole
Next step is to find the atomic weight of element X
Recall, Mole = racting mass / molar mass
Mass of X = (23.9 - 3.2)
Mass of X = 20.7 gram
Reacting mass = mole x molar mass
Atomic weight = reacting mass / mole
Atomic weight = 20.7 /0.1
Atomic weight = 207 g/mol
The element with atomic weight 207 is lead (Pb)