$word_{count}$: 200

H2O2 calculations: Volume strength = 11.2 x Molarity = 5.6 x Normality. n-factor = 2 always. Equivalent weight = 17. For percentage: % w/v = $\frac{Molarity x 34}{10}$.

Stoichiometry with KO2: 4KO2 + 2CO2 → 2K2CO3 + 3O2. Mole ratios: 4:2:2:3. Always start from the given moles and use the ratio.

Hardness calculations: 1 mol Na2CO3 (106 g) removes 1 mol $Ca^{2+}$. For ppm: mg/L directly, then convert to moles.

Lattice energy and solubility: If lattice energy >> hydration energy → insoluble. If they're close, entropy decides. For similar salts: compare the rate of change of LE vs HE with cation size.

Common numerical traps: (1) Forgetting that CaH2 gives 2 mol H2 per mol. (2) Confusing volume strength formula (11.2 for M, 5.6 for N). (3) Using wrong stoichiometry for Na2O2 + H2O (ratio is 2:2:4:1 for Na2O2:H2O:NaOH:O2). (4) Not distinguishing limited vs excess O2 for alkali metal oxide products.

Key formula sheet: Vol strength = 11.2M; Ksp(Ca(OH)2) = 4$s^3$; 4KO2 → 3O2; 2Na2O2 → 1O2; LE proportional to $\frac{q1q2}{r+ + r-}$.