c Physical Sciences Concepts:
The student produces evidence that demonstrates
understanding of chemical reactions, such as everyday examples of
chemical reactions.
 
The student expresses understanding of the nature of chemical reactions
in the concise explanations of the effects of buffers on [hydrogen]
ion concentration.
 The student’s
explanation of why calcium carbonate is not a good buffer demonstrates
an understanding of the role of ionic dissociation in a subsequent
chemical reaction.
a Scientific Connections and Applications:
The student produces evidence that demonstrates understanding of
big ideas and unifying concepts, such as…cause and effect.
The student
explicitly states that increasing the proportion of Na2HPO4
(sodium hydrogen phosphate) in relation to the acid will result
in the release of more ions.
Throughout the answer to question 1 and especially at  ,
the student expresses the results of the investigation as causal
relationships.
 In the answer
to question 2, the student clearly states the chemical cause behind
the sudden change in the pH data.
b Scientific Connections and Applications:
The student produces evidence that
demonstrates understanding of the designed world, such as the reasonableness
of technological designs.
 Throughout the
answer to question 6, the student logically and correctly identifies
scientific limitations to the use of lime in neutralizing an acidic
lake. The student’s statements are actually conclusions based
on the outcome of the investigation.
 At the end of
the answer to question 6, the student describes a fundamental societal
limitation—economic—on large-scale use of lime to neutralize
an acidic lake.
a Scientific Thinking: The
student…identifies variables in experimental and non-experimental
research settings.
The student
correctly identifies the proportion of Na2HPO4
as the variable that determines its capacity to absorb acid.
 The student
correctly identifies the addition of lime as a variable that will
increase pH, and states that the addition of other acids—another
variable—will lower the pH.
 The student
notes the simultaneous effects of two variables in this statement.
b Scientific Thinking: The
student uses concepts from Science Standards 1 to 4 to explain a
variety of observations and phenomena.
 The student
uses understanding of
c, specifically ionization and buffering, to explain the
phenomena observed.
 The student
applies understanding of
c to a new situation in the suggestion that biological (“organic”)
inhabitants of a lake may excrete basic substances, and that introduction
of such species into a damaged lake might provide natural buffering.
a Scientific Tools and Technologies:
The student uses technology and
tools…to observe and measure…with appropriate consideration
of accuracy and precision.
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The student’s collection of data demonstrates competence in
using lab equipment (pH meter and equipment for titration) and the
ability to observe and accurately measure phenomena. The student
demonstrated appropriate consideration of accuracy and precision
by recording consistent significant figures.
The student’s data are expressed in both table and graph forms.
The graph organizes data from the table so that a viewer can instantly
compare the buffering abilities of sodium phosphate and water.