Science Assessment ~ Ideas ~ A pure substance has characteristic properties, such as density, a boiling point, and solubility, all of which are independent of the amount of the substance and can be used to identify it.

Key Idea: Many substances react chemically in predictable ways with other substances to form new substances with different characteristic properties.

Sub-Ideas
Items & Student Performance
Misconceptions
NGSS

Students are expected to know that:

When substances react chemically one or more new substances are formed.
If a new substance does not appear, a chemical reaction did not occur.
The products of a chemical reaction can be identified as new substances because each product has different characteristic properties from the original substances under the same conditions.
Liquids, solids, or gases can be reactants or products in chemical reactions.
It is possible for a single substance to undergo a chemical reaction, such as when the substance is heated or an electrical current flows through the substance.
It is not true that all chemical reactions are irreversible.

Boundaries:

Students are not expected to know that chemical reactions involve the rearrangement of atoms into new molecules. This idea is addressed in a later idea (Idea D).
Students are also not expected to know that nuclear reactions are not chemical reactions nor why nuclear reactions are not chemical reactions. Nuclear reactions are addressed in later ideas (4E/H6* and 4G/H6*)
By “predictable ways,” we mean that the same products will be formed when the same reactants are combined regardless of location and experimental set-up. Students are not expected to predict what the products of a reaction will be.
Students are expected to know that the original substances in a chemical reaction are called reactants and the resulting substances are called products but they will not be assessed on these definitions.

Percent of students answering correctly (click on the item ID number to view the item and additional data)
Item ID Number	Knowledge Being Assessed	Pre-Test	Post-Test
SB045002	Bubbles of gas forming as a seashell is placed in vinegar is an example of a chemical reaction.	74%	86%
SC069007	When a chemical reaction occurs, the characteristic properties of the products are different than the characteristic properties of the reactants. (This item used a table to show the properties of the substances.)	72%	80%
SB058001	If the characteristic properties of the ending substances are different than the characteristic properties of the starting substances, a chemical reaction occurred. (This item used a table to show the properties of the substances.)	50%	70%

Frequency of selecting a misconception
Misconception ID Number	Student Misconception	Pre-Test	Post-Test
SCM020	A chemical reaction occurs when a substance dissolves (Novak et al., 1991; BouJaoude, 1992; Abraham et al., 1994; Ahtee et al., 1998; Stavridou et al., 1998; Valanides, 2000; Eilks et al., 2007)	20%	12%
SCM038	Chemical reactions involve two reactants (Cavallo et al., 2003; Eilks et al., 2007).	19%	9%
M009	Chemical reactions require heat in order to occur.	8%	5%
SCM056	A chemical reaction always happens when two liquids are combined together (DeBoer et al., 2008).	7%	7%
M003	All changes to matter involve chemical reactions.	7%	6%
SCM036	A chemical change is irreversible (Cavallo et al., 2003; Calik et al., 2005).	6%	5%
SCM019	A chemical reaction occurs during a change of state (Hall, 1973; Novak et al., 1991; BouJaoude, 1992; Ahtee et al., 1998; Stavridou et al., 1998).	4%	2%

Frequency of selecting a misconception was calculated by dividing the total number of times a misconception was chosen by the number of times it could have been chosen, averaged over the number of students answering the questions within this particular idea.

NGSS Statements
Code	Statement
PS1.A MS	Each pure substance has characteristic physical and chemical properties (for any bulk quantity under given conditions) that can be used to identify it.
PS1.B MS	Substances react chemically in characteristic ways. In a chemical process, the atoms that make up the original substances are regrouped into different molecules, and these new substances have different properties from those of the reactants.