How many grams of oxygen is required for the complete combustion of 39g of potassium.

Decision:
1. Let’s compose the reaction equation:
4K + O2 = 2K2O – redox reaction, potassium oxide obtained;
2. Let’s calculate the molar mass of substances:
M (K) = 39 g / mol;
M (O2) = 16 * 2 = 32 g / mol;
3. Determine the number of mol of potassium, if its mass is known:
Y (K) = m / M = 39/39 = 1 mol;
4. Let’s make the proportion according to the equation:
1 mol (K) – X mol (О2);
-4 mol       -1 mol hence, X mol (O2) = 1 * 1/4 = 0.25 mol;
5. Let’s calculate the mass of oxygen by the formula:
M (O2) = Y * M = 0.25 * 32 = 8 g.
Answer: to carry out the reaction you need 8 g of oxygen.