2021 AP Exam Administration Scoring Guidelines AP Chemistry AP ® Chemistry Scoring Guidelines 2021 © 2021 College Board College Board, Advanced Placement, AP, AP Central, and the acorn logo are regist[.]
2021 AP Chemistry đ Scoring Guidelines â 2021 College Board College Board, Advanced Placement, AP, AP Central, and the acorn logo are registered trademarks of College Board Visit College Board on the web: collegeboard.org AP Central is the official online home for the AP Program: apcentral.collegeboard.org AP® Chemistry 2021 Scoring Guidelines Question 1: Long Answer (a) point For the correct expression: Ka = (b) 10 points [H 3O + ][HCOO − ] [HCOOH] For the correct calculated concentration of H3O+: I C E point → H O+ + HCOO– HCOOH + H2O ← 0.25 0 –x +x +x 0.25 – x x x x2 Let [H 3O ] = x, then 1.8 × 10 = (0.25 − x) x2 Assume x Ksp), the introduction of SO42− as a common ion shifts the equilibrium towards the formation of more CaSO4(s) Total for question points â 2021 College Board APđ Chemistry 2021 Scoring Guidelines Question 7: Short Answer (a) points point For the correct calculated value: Accept one of the following: ã 0.325 mol O ì 32.00 g O = 10.4 g O mol O m 10.4 g = = 1.31 g/L V 7.95 L m P( MM ) (1.0 atm)(32.00 g/mol) = = = = 1.31 g/L D L ⋅ atm (0.08206 mol )(298 K) V RT ⋅K D = • (b) point For the correct answer and a valid justification: Accept one of the following: • • No, the density of the gas remains constant because P, R, and T remain constant AND the mass and volume of O2 decrease proportionately A mathematical justification is shown below D = (c) m = V n moles of O × molar mass of O = nRT P P × (molar mass of O ) RT point For a valid explanation: Accept one of the following: (d) • As the gas cools, the average kinetic energy (speed) of the O2 molecules decreases The molecules rebound with less energy when they collide with each other and the walls of the container The spacing between particles decreases, causing the volume occupied by the gas to decrease • As the gas cools, the average kinetic energy (speed) of the O2 molecules decreases The molecules rebound with less energy when they collide with each other and the walls of the container The only way for the molecules to maintain a constant rate of collisions with the walls of the container (maintaining a pressure of 1.00 atm) is for the volume of the gas to decrease point For a valid explanation: The ideal gas law assumes that gas particles not experience interparticle attractions As a real gas cools further, the intermolecular forces have greater effect as the average speed of the molecules decreases, resulting in inelastic collisions To maintain a gas pressure of 1.00 atm, the volume must decrease to accommodate more collisions with less energy Total for question points © 2021 College Board ... = = 0.035 M 6.3 6.3 = y mx = Estimated value from the graph within the specified range â 2021 College Board AP? ? Chemistry 2021 Scoring Guidelines (g) point For the correct answer: The concentration... reaction the net amount of catalyst is constant Total for question 10 points © 2021 College Board AP? ? Chemistry 2021 Scoring Guidelines Question 2: Long Answer (a) 10 points (i) For the correct answer:... sufficient thermal energy to overcome the activation energy of the reaction â 2021 College Board AP? ? Chemistry 2021 Scoring Guidelines (g) point For the correct peak height and location: The peak should