Calculate the mass of oxygen that can be obtained from potassium permanganate weighing 7.9 g.

To solve, we compose the equation:
1. 2KMnO4 = K2MnO4 + MnO2 + O2 – decomposition, oxygen was obtained by laboratory method;
2. Calculations:
M (KMnO4) = 158 g / mol.
M (O2) = 32 g / mol.
3. Determine the Y (amount) of the original substance:
Y (KMnO4) = m / M = 7.9 / 158 = 0.05 mol.
4. Proportion:
0.05 mol (KMnO4) – X mol (O2);
-2 mol -1 mol from here, X mol (O2) = 0.05 * 1/2 = 0.025 mol.
5. Find the mass of the product:
m (O2) = Y * M = 0.025 * 32 = 0.8 g.
Answer: oxygen with a mass of 0.8 g was formed.