Kb=KwKa=1.0×10-144.0×10-4=2.5×10-11cap K sub b equals the fraction with numerator cap K sub w and denominator cap K sub a end-fraction equals the fraction with numerator 1.0 cross 10 to the negative 14 power and denominator 4.0 cross 10 to the negative 4 power end-fraction equals 2.5 cross 10 to the negative 11 power :
The 1972 AP Chemistry Free-Response section featured several classic problems covering stoichiometry, thermodynamics, and acid-base chemistry. Below are detailed solutions and explanations for the primary questions released from that year. 1. Stoichiometry and Gas Laws (Acid-Base Mixture) : A 5.00g sample mixture of KOHcap K cap O cap H KClcap K cap C l is reacted with 0.100L0.100 cap L 2.00M2.00 cap M HClcap H cap C l . The reaction produces 249mL249 m cap L CO2cap C cap O sub 2 740torr740 t o r r ). The excess HClcap H cap C l is titrated with 86.6mL86.6 m cap L 1.50M1.50 cap M NaOHcap N a cap O cap H Part A: Percentage of in the mixture Find moles of CO2cap C cap O sub 2 : Use . Convert units: CO2cap C cap O sub 2 Find mass of : From the balanced equation 1972 ap chemistry free response answers
concentration remains essentially stable, leading to a negligible pH change [6]. Kb=KwKa=1
Weak acids/bases, buffer systems, and titration calculations. Stoichiometry and Gas Laws (Acid-Base Mixture) : A 5
The half-reactions for the electrolysis of molten sodium chloride (NaCl) are:
Ptotal=PNO2+PN2O4cap P sub total end-sub equals cap P sub cap N cap O sub 2 end-sub plus cap P sub cap N sub 2 cap O sub 4 end-sub :
The answer is negative , indicating exothermic. In 1972, many students forgot to multiply O₂ by zero and lost a point.