SPEAK OUR LANGUAGE

• CELL – Core Experience Learning Lab
• SDR – Scientist Data Record

ASK WHY

Great scientists question the world around them. We encourage our LabLearner students to do the same. In anticipation of this, we explain the importance of learning the concepts in the Ask Why section within the CELL. Our hope is that these explanations help students understand why science matters.

BRANCH OUT

Each Investigation introduces students to a different branch of science or STEM (Science, Technology, Engineering, Mathematics) career that utilizes the scientific concepts of the CELL. These real-world connections will help students see the relevance of what they are learning. STEM connections are also integrated into each Performance Assessment.

GET FOCUSED

The Focus Questions in each Investigation are designed to help teachers and students focus on the important concepts. By the end of the CELL, students should be able to answer the following questions:

Investigation 1:

• Can you tell the difference between an element and a compound by measuring mass and volume? It is likely that students will not be able to discern the difference between substances that are elements and those that are compounds because many of the properties such as color, texture, visual appearance, mass, and volume are similar for many of the substances.

• Can you determine the identity of an unknown substance by observing its mass and volume? Students will likely indicate that without previous knowledge of the properties of all elements and compounds or samples of known elements or compounds at their disposal, a definite identification using just mass and volume is not possible.

Investigation 2:

• Can you tell the difference between an element and a compound by calculating density and observing chemical reactions? It is likely that students will not be able to discern the difference between substances that were elements and those that were compounds during the course of their investigation.

• Can you determine the identity of an unknown substance by calculating its density and observing chemical reactions? Students may or may not suggest possible identities of the substances based on similarities of color and texture to substances that they encounter in everyday life.

Investigation 3:

• Do compounds composed of the same elements have identical properties? Not necessarily.

• Can compounds composed of different elements have similar properties? Yes.

Investigation 4:

• Do compounds composed of the same elements have a similar or dissimilar pH? Compounds composed of the same elements may have a pH that is either similar or dissimilar to each other.

• Do all liquid compounds have the same pH? The pH of each liquid compound in our investigation was dissimilar from that of the other liquid compounds.

• Do all solid compounds have the same pH? Yes and no.

Note: These are succinct responses to the Focus Questions and are placed here for easy reference. Fully developed responses to the Focus Questions can be found on each PostLab page.

Note: Some questions may be revisited as the CELL progresses. As students acquire additional knowledge, their responses should reflect this.

LEARN THE LabLearner LINGO

The following list includes Key Terms that are introduced within the CELL. These terms should be used, as appropriate, by teachers and students during everyday classroom discourse.

Note: Additional words may be bolded within the Backgrounds. These words are not Key Terms and are strictly emphasized for exposure at this time.

Investigation 1:

• Matter: anything that takes up space and has mass
• Element: a type of matter that cannot be broken down into another substance by chemical reactions
• Compound: a type of matter that is made up of two or more elements
• Physical Property: a property of a substance that can be observed without changing the substance’s identity

Investigation 2:

• Density: a property of matter that defines how much matter exists in a particular space

Investigation 3:

• Solubility: the ability of a solid to dissolve in a liquid
• Miscibility: the ability of a liquid to mix with another liquid

Investigation 4:

• pH: a property used to describe whether a compound is an acid, base, or neutral substance

BE PREPARED

An overview of the materials for each lab is placed here for easy reference. Specific teacher preparation for the labs is placed at the beginning of each Lab page.

EXTEND YOUR THINKING

The following information is included so that teachers have additional background knowledge pertaining to the concepts introduced in the CELL. Teachers may choose to use this information enrich students during instruction, but this is optional and not necessary for the intended students’ learning outcomes.

What is matter? Matter is described as anything that takes up space and has mass. Within our universe, matter can and has been described in various ways. Early civilizations such as the Greeks believed that matter arose from four basic ingredients or elements: earth, wind, air and fire. They believed these elements to be pure or unable to be broken down to other forms of matter. Although the substances they identified as elements were incorrect, the concept of elements exists in our present understanding and description of matter. Elements are currently defined as substances that cannot be broken down to other substances by chemical reactions. Common examples of elements include copper, gold, silver, oxygen and chlorine.

Early in the 19th century, Dmitri Mendeleev constructed what he termed the Periodic Table, an organized grouping of the elements known at the time. The organization of the table was based on the chemical and physical properties of the elements, and categorized the elements by similarities in chemical and physical properties. Although the modern Periodic Table includes over 100 elements, more than in Mendeleev’s time, the organization remains the same.

Elements, however, represent neither the largest or smallest classification of matter. Elements are composed of atoms, which have been described as the smallest units of matter that still retains the properties of an element. Still smaller are subatomic particles such as electrons, protons and neutrons that compose an atom. Ultimately it is the subatomic organization that governs the characteristics of an element. Every property of an element, whether a chemical or physical property, is due to the element’s atomic structure (number and arrangement of subatomic particles). Differences and similarities between elements, therefore, can be explained by similarities or differences at the subatomic level.

Because elements are not the largest classification of matter it is not surprising that other forms of matter may result from the combination of elements. Compounds are substances which consist of wo or more elements combined in a fixed ratio. For example, water (H2O) consists of two atoms of hydrogen and one atom of oxygen. One of the most interesting features of compounds is that their properties result from the unique combination of atoms rather than the simple presence of an atom. Think back to our example of water. Both oxygen and hydrogen, in elemental forms, are gases whereas water is a liquid. Another example is sodium chloride or table salt. Sodium chloride (NaCl) is composed of the elements sodium and chlorine. Sodium is a highly reactive metal and chlorine a poisonous gas. Yet when the two are chemically combined, the resulting compound is an edible solid. Ultimately the properties of compounds can also be attributed to atomic structure, a structure that differs from each of the compound’s contributing elements.

Atomic and subatomic particles, however, are impossible to discern from visual observation. Instead, differences in atomic and subatomic structure can be inferred by examination of a compound’s or element’s physical or chemical properties. Physical properties refer to those properties that can be observed or measured without changing the identity of the compound. Examples of physical properties include color, hardness, density, solubility, boiling point and melting point. Chemical properties are defined as those that govern how a compound changes or reacts to form other substances. Examples of chemical properties include changes in pH, oxidation and combustion. The investigations with this Core Experience Learning Lab are designed to explore the physical and chemical properties of elements and compounds. Investigations One and Two focus on the physical properties of color, texture, hardness and density and chemical reactions with specific compounds.

The density of elements and compounds may be a new property that students need to consider. Density is a property of matter that defines the amount of matter that exists in a particular space. Strictly speaking, density is defined as mass per unit volume or g/cm3, and can be calculated if the mass and volume of a substance are known. Using the formula for density (density= mass/volume) students will calculate and compare the densities of unknown samples of elements and compounds. Although not explicitly stated during these investigations, students may discover that density is an intensive property of matter. That is, it is independent of the amount or volume of matter. The reason for this lies in the relationship between the two parameters, mass and volume, by which density is determined. Mass and volume are directly proportional to each other. As the volume of a substance increases or decreases, so does it mass. Likewise as the mass of a substance increases or decreases, so does its volume. Thus whether 10 grams or 5 grams of a substance is used for determination of density, the density will be the same because the larger mass of matter will have a correspondingly larger volume.

In addition to exploration of properties such as density, one of the underlying concepts in these investigations is that some of the physical and chemical properties of elements and compounds are similar. This concept may be a surprise to students, as a common misconception is that elements and compounds will have apparent and visually distinctive physical and chemical properties because they are defined in reference sources as different types of matter. What students will find in the Core Experience Learning Lab investigations is that the color, texture, and visual signs of chemical reactivity with specific compounds are similar between elements and compounds, and identification based only on a few limited physical and chemical properties does not often permit a definitive identification of a substance as an element or compound. Rather, identification of substances should involve a detailed investigation into many of the substances properties, as well as comparison of these properties to known elements or compounds.

From these first two investigations, students extend their exploration into the properties of matter by narrowing their focus to three properties of compounds: solubility, miscibility and pH. Solubility and miscibility are terms used to describe how well solids and liquids dissolve in other liquids. Solubility refers to the ability of a solid to dissolve in a liquid. Miscibility refers to the ability of a liquid to mix with another liquid. Both solubility and miscibility are considered physical properties. When exploited, miscibility can also be used to illustrate differences in the densities of liquids. If two liquids are miscible the difference in their densities cannot be determined merely by visual observation because the two liquids mix to create one uniform solution. When two liquids are immiscible, however, the liquid that is less dense will remain on top of or float on the more dense liquid.

pH, the final property that students will investigate, is considered a chemical property and is used to describe the acid or base properties of a substance. A numerical scale that extends from 0 to 14 is used to denote the property of pH. Substances with a pH less than 7 are considered acidic, those with a pH greater than 7 are basic, and those with a pH of 7, neutral. Acids and bases are reactive with certain elements and compounds as well as with each other. Thus the property of pH is often used to predict chemical reactions or select compounds for specific chemical reactions.

In this Core Experience Learning Lab, students will study each of these properties as a way of addressing the larger concept that the properties of a compound result from the unique combination of elements that compose the compound rather than from the individual properties of each element. As a result of their investigations students should conclude that properties of compound such as solubility, miscibility and pH depend upon the combination and number or ratio of the atoms of elements within compounds rather than simply the presence of an element. Therefore, compounds composed of the same elements can and often do have different properties and compounds composed of different elements may have similar properties. Ultimately it is these types of observations and analyses that lead students to consider that differences in properties may ultimately lie in understanding the atomic and subatomic structure of matter.

Note: In this Core Experience Learning Lab, table salt is listed as a compound with the formula NaCl (sodium chloride). Although sodium chloride is the major ingredient in table salt, table salt is technically a mixture rather than a pure compound, because it also contains silica particles to prevent clumping and potassium iodide as an dietary iodine source. However, the properties of table salt, which students will investigate in this module, are similar to those of pure sodium chloride.