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Step-by-step approach for Raoult's law problems: (1) Identify if solution is ideal or shows deviations. (2) Convert given masses to moles using molar masses. (3) Calculate mole fractions: x_A = n_A/(n_A + n_B). (4) Apply P_A = x_A*P_A_std for each component. (5) Find P_total = P_A + P_B. (6) For vapour composition: y_A = P_A/P_total. Common problem types: Given x_A and P_std values, find P_total and y_A. Given y_A and P_std values, find x_A (requires algebra). Given P_total and one P_std, find the other or find composition. For non-volatile solute: P_solution = x_solvent * P_solvent_std. RLVP = delta_P/P_std = x_solute. Traps: (a) confusing mass fraction with mole fraction, (b) not converting grams to moles before calculating x, (c) using RLVP formula when both components are volatile, (d) forgetting that y_A + y_B = 1. For immiscible liquids: P_total = P_A_std + P_B_std (each exerts full vapour pressure). This is tested as steam distillation problems.