Topic: Substances, Chemical Reactions, and Conservation of Matter

Below is a list of key ideas related to Substances, Chemical Reactions, and Conservation of Matter. For each key idea, you will find a list of sub-ideas, a list of items, results from our field testing, and a list of student misconceptions. After clicking on a tab, click on it again to close the tab.

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.

Students are expected to know that:

  1. Note: The term “characteristic property” is used to emphasize that these properties are defining attributes that are independent of the amount of the sample, regardless of time, location, size, or shape.
  2. The term “substance” means a pure material that is made of the same matter throughout. This is in contrast to the common definition that equates substance with matter that could be made of either a single substance or a mixture of more than one substance. To make this explicit, the phrase “pure substance” is used in assessment items.
  3. A substance can be a solid, a liquid, or a gas.
  4. Every substance has a set of characteristic properties that are always the same for that substance, regardless of time, location, shape, or size.
  5. Furthermore, characteristic properties are consistent throughout a sample of a substance.
  6. Characteristic properties with which students should be familiar are boiling point, melting and freezing point, solubility (i.e. how much of the substance can dissolve in water), flammability (i.e. the ease with which a substance will catch on fire), odor, color, and density (i.e., that equal volumes of different substances have different masses).
  7. Weight, mass, volume, shape, length/width, texture, and temperature are not characteristic properties of substances and may change.
  8. The characteristic properties of a substance do not change when temperature and pressure remain the same.
  9. No two substances can have the same set of characteristic properties under the same conditions and that if two materials have even one different characteristic property, they are different substances.

Boundaries:

  1. Students are not expected to know that the properties of substance can be different at the nanoscale.
  2. They are not expected to know the formula for density (density = mass/volume).
  3. Students are not expected to know that the atomic mass of a substance is a characteristic property.
  4. They are not expected to know whether specific materials are or are not pure substances.
  5. Because some properties do change with changing conditions (e.g., changing atmospheric pressure affects boiling point) all assessment items will make comparisons between substances where it is clear that the conditions, such as temperature and pressure, are constant.
Percent of students answering correctly (click on the item ID number to view the item and additional data)
Item ID
Number

Knowledge Being Assessed

Grades
6–8

Grades
9–12

Select This Item for My Item Bank

SC095003

To help identify a metal, you could determine its density and compare it to the density of other metals.

56%

61%

SC095002

To help identify a metal, you could determine its melting point and compare it to the melting point of other metals.

55%

59%

SC064007

Two liquids with the same density and color but different boiling points are different substances. (This item uses a table that lists properties of the liquids.)

53%

54%

SC063004

To identify a liquid, you could determine the boiling point of the liquid and compare it to the boiling points of other liquids.

50%

58%

SC057008

Two solids with the same melting point and color could be the same substance. (This item uses a table that lists properties of the solids.)

46%

57%

SC044004

If a piece of wax is removed from a ball of wax, the mass of the ball of wax would change but its melting point would stay the same.

46%

59%

SC057007

Two solids with the same melting point and color could be the same substance. (This item uses a table that lists properties of the solids.)

46%

56%

SC046005

How much of a substance dissolves in water is a characteristic property of the substance.

35%

52%

SC100003

Two liquids with the same flammability, boiling point, and color could be the same substance. (This item uses a table that lists properties of the solids.)

37%

47%

SC064008

Two liquids with the same density and color but different boiling points are different substances. (This item uses a table that lists properties of the liquids.)

41%

43%

SC100004

Two liquids with the same boiling point and color could be the same substance. (This item uses a table that lists properties of the liquids.)

31%

44%

SC099002

Determining the mass of a liquid and comparing its mass to the mass of other liquids will NOT help you identify the liquid.

30%

36%

SC061004

Smelling two liquids can help a student determine if the liquids are the same substance.

29%

34%

Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

Grades
6–8

Grades
9–12

SCM053

If two substances share one characteristic property, they are the same substance (AAAS Project 2061, n.d.).

35%

34%

SCM069

The melting point of a substance is dependent on the amount of substance. For example, the melting point of a ball of wax will change if a piece of wax is removed from the ball (AAAS Project 2061, n.d.).

39%

27%

SCM079

Melting point is not a characteristic property of a pure substance.

32%

27%

SCM058

Volume is a characteristic property of a substance (DeBoer et al., 2009).

31%

26%

SCM076

Color is not a characteristic property of a pure substance (AAAS Project 2061, n.d.).

29%

24%

SCM078

Boiling point is not a characteristic property of a pure substance.

21%

22%

SCM081

Density is not a characteristic property of a pure substance.

21%

21%

SCM054

If most of the listed characteristic properties are the same, the substances are the same (AAAS Project 2061, n.d.).

20%

22%

SCM023

Temperature is a characteristic property of the substance (Thomaz et al., 1995).

20%

18%

SCM057

Mass/weight is a characteristic property of a substance (DeBoer et al., 2009).

20%

18%

SCM080

Freezing point is not a characteristic property of a pure substance.

20%

16%

SCM077

Flammability is not a characteristic property of a pure substance.

15%

15%

SCM061

Shape is a characteristic property of a substance (AAAS Project 2061, n.d.).

12%

10%

SCM060

Length is a characteristic property of a substance (AAAS Project 2061, n.d.).

10%

11%

SCM059

Width is a characteristic property of a substance (AAAS Project 2061, n.d.).

11%

7%

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.

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

Students are expected to know that:

  1. When substances react chemically one or more new substances are formed.
  2. If a new substance does not appear, a chemical reaction did not occur.
  3. 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.
  4. Liquids, solids, or gases can be reactants or products in chemical reactions.
  5. 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.
  6. It is not true that all chemical reactions are irreversible.

Boundaries:

  1. 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).
  2. 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*)
  3. 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.
  4. 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.
Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

Grades
6–8

Grades
9–12

SCM038

Chemical reactions involve two reactants (Cavallo et al., 2003; Eilks et al., 2007).

66%

58%

SCM036

A chemical change is irreversible (Cavallo et al., 2003; Calik et al., 2005).

36%

34%

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)

29%

21%

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).

19%

16%

SCM070

A chemical reaction always happens when two substances are combined together (AAAS Project 2061, n.d.).

18%

16%

SCM040

Chemical reactions involve only the production of gas (Cavallo et al., 2003).

11%

13%

SCM039

Chemical reactions involve liquids only (Cavallo et al., 2003).

13%

11%

SCM056

A chemical reaction always happens when two liquids are combined together (DeBoer et al., 2008).

15%

9%

SCM063

Chemical reactions occur between solids and liquids but not between solids and gases (AAAS Project 2061, n.d.).

12%

10%

SCM037

All chemical reactions are inherently dangerous (Cavallo et al., 2003).

11%

11%

SCM062

A solid substance is always formed during a chemical reaction (DeBoer et al., 2008).

9%

8%

SCM002

A chemical reaction must take place in a laboratory (Herrmann-Abell et al., 2009).

8%

7%

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.

When substances interact to form new substances, the atoms that make up the molecules of the original substances rearrange into new molecules.

Students are expected to know that:

  1. During a chemical reaction the atoms that are linked together in molecules (or arranged in other patterns such as arrays and crystals) rearrange to make new molecules.
  2. If the atoms are not rearranged, then a chemical reaction has not occurred.
  3. New substances are made of the same kinds of atoms as the original substances (i.e., the atoms themselves did not change during the reaction).

Boundaries:

  1. The idea that the number of each kind of atom stays the same will be assessed under Idea H (conservation of matter).
  2. Students are not expected to know the term “bond” or how chemical bonds are formed or broken during chemical reactions.
  3. They are not expected to know that during chemical reactions, atoms are not turned into energy.

Whenever substances within a closed system interact with one another, the total mass of the system remains the same.

Students are expected to know that:

  1. When substances mix, undergo chemical reactions, change state, or dissolve, or when objects are cut or broken into smaller pieces, the total mass of all the matter will always remain the same.
  2. Regardless of the form that the products of these processes may take (for example, when a sugar cube dissolves in water or a chemical reaction produces a gas), the mass will always stay the same.
  3. If it appears that the mass has changed, it is because some material has not been accounted for.
  4. Because light is not matter, its presence or absence does not affect the mass of the matter.

Boundaries:

  1. Students are not expected to know that mass is not conserved in energy-mass conversions such as nuclear reactions or other subatomic interactions.
  2. Note: The words “weight,” “weigh,” and “mass” are used appropriately in the assessment items. The students are not expected to know the difference between “weight” and “mass.”
Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

Grades
6–8

Grades
9–12

SCM029

Mass is not conserved during processes in which gases take part (Mas et al., 1987; Berkheimer et al., 1988; Hesse et al., 1992). If a gas is produced during a chemical reaction that takes place in a closed system, the total mass decreases (Ozmen et al., 2003).

55%

50%

SCM032

In a closed system, the total mass increases during a precipitation reaction (Barker et al., 1999; Ozmen et al., 2003).

54%

49%

SCM064

When a liquid in a closed container is heated, the mass of the liquid increases as the liquid expands (AAAS Project 2061, n.d.).

48%

34%

SCM041

During biological decomposition in a closed system, the total mass of the system decreases (Mitchell et al., 1984).

41%

32%

SCM028

In a closed system, mass decreases after a solid dissolves in a liquid (Stavy, 1990b; Ozmen et al., 2003).

27%

20%

SCM027

When a chemical reaction occurs, matter just disappears. For example, gasoline is used up in the car and disappears (Andersson, 1986).

16%

11%

SCM051

Mass increases after a solid dissolves in a liquid (Stavy, 1990b).

15%

13%

SCM010

Matter can disappear with repeated division, dissolving, evaporation, or chemical change (Smith et al., 2004).

10%

10%

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.

Whenever atoms interact with each other, regardless of how they are arranged or rearranged, the total mass stays the same.

Students are expected to know that:

  1. Atoms are not created or destroyed when substances mix, undergo chemical reactions, change state, or dissolve, or when objects are cut or broken into smaller pieces.
  2. The total number of each kind of atom always remains the same regardless of what happens to the matter (mixing, chemical reactions, changes of state, dissolving, or objects being cut or broken into smaller pieces).
  3. The mass of an atom does not change.
  4. If the measured mass has changed, it is because some atoms have not been accounted for.

Boundaries:

  1. Students are not expected to know that mass is not conserved in energy-mass conversions such as nuclear reactions or other subatomic interactions.
Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

Grades
6–8

Grades
9–12

SCM083

New atoms are created during chemical reactions (AAAS Project 2061, n.d.).

49%

34%

SCM075

Atoms can be destroyed during a chemical reaction (AAAS Project 2061, n.d.).

34%

26%

SCM029

Mass is not conserved during processes in which gases take part (Mas et al., 1987; Berkheimer et al., 1988; Hesse et al., 1992). If a gas is produced during a chemical reaction that takes place in a closed system, the total mass decreases (Ozmen et al., 2003).

30%

29%

SCM068

The mass of a closed system will increase if a new kind of molecule is formed in the system (AAAS Project 2061, n.d.).

30%

19%

SCM066

The number of different kinds of molecules, not the number of each kind of atom, is always conserved (AAAS Project 2061, n.d.).

20%

18%

SCM086

Atoms can become lighter during a chemical reaction (AAAS Project 2061, n.d.).

19%

13%

SCM065

The total number of atoms, not the number of each kind of atom, is always conserved (AAAS Project 2061, n.d.).

19%

13%

SCM067

The mass of a closed system will decrease if two substances combine to form one substance (AAAS Project 2061, n.d.).

16%

14%

SCM085

Atoms can become heavier during a chemical reaction (AAAS Project 2061, n.d.).

15%

13%

SCM005

The number of molecules is always conserved (Mitchell et al., 1984).

12%

10%

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.