Unit_7_Progress_Check_FRQ_ANS.pdf

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(1)

1. For parts of the free-response question that require calculations, clearly show the method used

The dissolution of is represented above.

(a) Write a mathematical expression that can be used to determine the value of , the molar solubility of . (Do not do any numerical calculations.)

(b) If is dissolved in , is the maximum possible concentration of in the solution greater than, less than, or equal to the concentration of in the solution in part ( ) ? Explain.

Compound

(c) A table showing values for several lead compounds is given above. A saturated solution of which of the compounds has the greatest molar concentration of ? Explain. (Do not do any numerical calculations.)

(2)

Select a point value to view scoring criteria, solutions, and/or examples and to score the response.

0 1

The response gives the equation OR (or a variation).

Part (b)

Select a point value to view scoring criteria, solutions, and/or examples and to score the response.

0 1 2

The response meets both of the following two criteria:

The amount of that dissolved in the solution is less than the amount of that dissolved in the original solution.

The high concentration of in the solution suppresses the dissolution of because less can form before the product equals or exceeds the value of .

Part (c)

Select a point value to view scoring criteria, solutions, and/or examples and to score the response.

0 1

(3)

has the largest .

2. For parts of the free-response question that require calculations, clearly show the method used

Gas Initial Concentration ( ) 0.030

0.015

Samples of three gases, , , and , were combined in a rigid vessel. The initial concentrations of and are given in the table above.

(4)

Equilibrium was established at a certain temperature according to the following chemical equation.

After equilibrium was established, the concentration of was .

(b) On the graph above, carefully draw three curves, one for each of the three gases, starting from the initial points you drew in part ( ). The curves must show how the concentration of each of the three gases changed as equilibrium was established.

, , and are at equilibrium at a different temperature in a different vessel.

(5)

(d) Does the value of increase, decrease, or remain the same when the temperature is decreased? Justify your answer based on the expression for and the concentrations of the product and reactants.

(e) In the following empty box, draw an appropriate number of each type of molecule to represent a possible new equilibrium at the lower temperature.

Part (a)

Select a point value to view scoring criteria, solutions, and/or examples and to score the response.

0 1 2

The diagram meets both of the following criteria:

(6)

The partial pressure of is plotted at at time , and the point is labeled.

Part (b)

Select a point value to view scoring criteria, solutions, and/or examples and to score the response.

0 1 2 3

The response meets all of the following criteria:

The curve for decreases to and levels off.

The curve for decreases to and levels off.

The curve for increases to and levels off.

Part (c)

Select a point value to view scoring criteria, solutions, and/or examples and to score the response.

0 1

The response indicates that the system shifts to the right because the forward reaction is exothermic.

Part (d)

(7)

0 1 2

The response meets both of the following criteria:

The response indicates that .

The response indicates that if and decrease and increases, must increase.

Part (e)

Select a point value to view scoring criteria, solutions, and/or examples and to score the response. The response should be consistent with the answer to part (d).

0 1 2

The response meets both of the following criteria:

There is one molecule and one molecule in the box.

References

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