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Descriptive Statements:
- Apply knowledge of chemical notation (e.g., chemical formulas, chemical equations, net ionic equations).
- Demonstrate knowledge of common types of chemical reactions (i.e., synthesis, decomposition, single replacement, double replacement, and combustion).
- Analyze chemical reactions using data to predict products (e.g., the solubility rules, the common oxidation states of elements, the activity series of metals and nonmetals, the properties of acids and bases).
- Demonstrate knowledge of common acid-base reactions, including neutralization.
- Demonstrate knowledge of oxidation-reduction reactions, including electrochemical cells.
Sample Item:
Automobile mechanics measure the density of the electrolyte solution of lead storage batteries to determine the amount of charge remaining. Which of the following statements describes the cause of the change in electrolyte density as the battery's charge decreases?
- The sulfuric acid electrolyte is consumed, and water is formed.
- Water evaporates, and the electrolyte concentration increases.
- The lead and lead(IV) oxide migrate from the solution to the electrodes.
- Lead in the electrolyte solution precipitates out of the solution.
Correct Response and Explanation (Show Correct ResponseHide Correct Response)
A. During the normal operation of a lead storage battery, elemental lead is oxidized and lead 4+ ions are reduced. Both half reactions produce lead(II) sulfate, consuming sulfuric acid. The reduction half reaction produces water. Sulfuric acid is more dense than water, therefore the density of the mixture decreases.
Descriptive Statements:
- Apply knowledge of the use of balanced chemical equations to represent chemical reactions.
- Apply knowledge of the mole, Avogadro's number, and their relationships to mass and particle number.
- Apply knowledge of mass percent data and the description of compounds through empirical or molecular formulas.
- Apply knowledge of stoichiometry to predict relationships between reactant(s) and/or product(s) (e.g., mole to mole, gram to gram, mole to particle, mole to liter).
- Apply stoichiometric reasoning to situations involving a limiting reagent.
- Demonstrate knowledge of common experimental techniques (e.g., titration, gravimetric analysis) for determining amounts of reactants and products.
- Analyze the results of investigations using mathematical tools (e.g., theoretical yield, actual yield, percent error) to evaluate their success.
Sample Item:
Use the chemical equation below to answer the question that follows.
N2(g) + 3H2(g) → 2NH3(g)Gaseous N 2 reacts with 3 gaseous H 2 to produce 2 gaseous N H 3
Given the reaction shown, how much NH3 is formed when 823 g of N2 are combined with 145 g of H2?
- 58.8 g
- 96.7 g
- 815 g
- 1650 g
Correct Response and Explanation (Show Correct ResponseHide Correct Response)
C. By calculating the number of moles of each reactant and analyzing the stoichiometric relationship between them, H2 can be identified as the limiting reactant. From the stoichiometric relationship between H2 and NH3, the number of moles of product formed can be calculated. This mole quantity can then be converted into mass using the molar mass of NH3.
Descriptive Statements:
- Apply knowledge of collision theory and its connections to qualitative factors affecting reaction rates (i.e., concentration, temperature, surface area, and catalyst).
- Analyze graphical and numerical representations (i.e., concentration, time, and rate) of reaction rates.
- Demonstrate knowledge of rate-determining steps in a reaction mechanism.
- Demonstrate knowledge of dynamic equilibrium in physical and chemical systems, including the equilibrium constant.
- Apply knowledge of Le Châtelier's principle and factors that can change equilibrium concentrations (e.g., temperature, pressure, amounts of reactants or products, presence of a common ion).
- Demonstrate knowledge of common applications of equilibrium systems (e.g., weak acid and base solutions, buffer solutions, electrochemical cells, solubility products).
Sample Item:
Use the chemical equation below to answer the question that follows.
Zn(s) + 2H+(aq) ⇌ Zn2+(aq) + H2(g)solid zinc reacts with 2 aqueous H plus ions to produce aqueous zinc 2 plus ions and gaseous H 2
What is the equilibrium constant expression for the reaction shown?
Correct Response and Explanation (Show Correct ResponseHide Correct Response)
B. When writing equilibrium constant expressions, pure solid and pure liquid compounds are omitted, as their concentrations are not dynamic, and the pressure of gaseous compounds can be used in place of concentration, as the two values will vary proportionally to one another. The equilibrium constant expression for this reaction is equal to the concentration of Zn2+(aq) × zinc 2 plus ions times the pressure of H2(g) H 2 gaseous each raised to a power equal to its stoichiometric coefficient, divided by the concentration of H+(aq) H plus ions aqueous raised to a power equal to its stoichiometric coefficient.
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