Chemical equations and stoichiometry
- 1 gram of sodium hydroxide was treated with 25 mL of 0.75 M HCl solution, the mass of sodium hydroxide left unreacted is equal to Answer: 3. 250 mg Key idea: find the limiting reagent for NaOH+HCl→ NaCl+H₂O . NaOH: 1/40=0.025 mol = 25 mmol. HCl: 25×0.75=18.75 mmol. Left... 1
- Which amongst the following options is correct graphical representation of Boyle's Law?(1) P vs T, straight lines through origin labelled V_1, V_2, V_3 with V_1<V_2<V_3; (2) P vs V, hyperbolas labelled T_1, T_2, T_3 with T_3>T_2>T_1; (3) P vs 1/V, st… Answer: 3. P vs 1/V lines, T ₃ >T ₂ >T ₁ (graph) Key idea: Boyle's law: at constant T, P ∝ 1/V , so P plotted against 1/V is a straight line... 1
- The right option for the mass of CO_2 produced by heating 20 g of 20% pure limestone is (Atomic mass of Ca = 40)CaCO_3 1200\ K CaO + CO_2 Answer: 3. 1.76 g Key idea: Only the pure CaCO₃ decomposes; find its moles and use 1:1 mole ratio with CO₂ . Pure CaCO₃ = 20 × 20/100 = 4 g.... 1
- What mass of 95% pure CaCO_3 will be required to neutralise 50 mL of 0.5 M HCl solution according to the following reaction ?CaCO_3(s) + 2HCl_(aq) → CaCl_2(aq) + CO_2(g) + 2H_2O_(l)[Calculate upto second place of decimal point] Answer: 3. 1.32 g Key idea: find moles of HCl, use the 1 : 2 stoichiometry, then correct for purity. Moles of HCl =0.5×0.050=0.025 mol. CaCO... 1
- The number of moles of hydrogen molecules required to produce 20 moles of ammonia through Haber's process is : Answer: 3. 30 N₂ + 3H₂ → 2NH₃ : 3 mol H₂ give 2 mol NH₃ . Moles of H₂ = 20×3/2 = 30 . Option (3). 1