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Water Purification


CA State Teaching Standards


Heat and Thermodynamics

3. Energy cannot be created or destroyed, although in many processes energy is transferred to the environment as heat.

d. Students know that most processes tend to decrease the order of a system over time and that energy levels are eventually distributed uniformly.

The Cu2+ exchanges for the Na+ because two Na+ ions are released into solution upon exchange.  Two ions in solution provide more disorder than one ion in solution, and this drives the reaction.

e. Students know that entropy is a quantity that measures the order or disorder of a system and that this quantity is larger for a more disordered system.

Example d above explains why exchange of Cu2+ for Na+ is entropically driven.  Adsorption of they dye molecule onto the carbon is also related to entropy.  When an organic molecule is dissolved in water, the water molecules around the organic molecule become very ordered, lowering the entropy of the system.  If the organic molecule is removed by adsorption onto the carbon, the entropy of the water increases.


Chemical Bonds

2.  Biological, chemical, and physical properties of matter result from the ability of atoms to form bonds from electrostatic forces between electrons and protons and between atoms and molecules. As a basis for understanding this concept:

Copper sulfate is held by opposite electrostatic charges between the ions.  Activated carbon filters the food coloring dye through van der Waals interactions.  Teachers can also explain how water molecules solvate copper and sulfate ions.  

a. Students know atoms combine to form molecules by sharing electrons to form covalent or metallic bonds or by exchanging electrons to form ionic bonds.

Yellow #6 is an organic molecule composed of covalent bonds among carbons, hydrogen, sulfur, and nitrogen in addition to ionic bonds between sodium and oxygen.  Copper sulfate (CuSO4) is comprised of ionic bonds, between the Cu2+ an SO42- ions; the sulfate ion is composed of covalent bonds between the S and O atoms.

b. Students know chemical bonds between atoms in molecules such as H2, CH4, NH3,H2CCH2, N2, Cl2, and many large biological molecules are covalent.

    The bonds in the dye molecule and within the sulfate ion (SO42-) are covalent.

c. Students know salt crystals, such as NaCl, are repeating patterns of positive and negative ions held together by electrostatic attraction.

CuSO4 is a salt.

d. Students know the atoms and molecules in liquids move in a random pattern relative to one another because the intermolecular forces are too weak to hold the atoms or molecules in a solid form.

Dissociation of the CuSO4 salt in water is by the screening of the ionic bonds between the Cu2+ and SO42- ions.

e. Students know how to predict the shape of simple molecules and their polarity from Lewis dot structures.

Polar, hydrophobic and hydrophilic interactions are important interactions necessary to understand how the zeolites and activated carbons adsorb the salt and dye.  The yellow dye molecule contains hydrophobic aromatic carbon rings that have a large affinity to the hydrophobic carbon rings of the activated carbon. The dye prefers to interact with the carbon rather than water. The copper ions are positively charged (hydrophilic), and the carbon is neutral and hydrophobic.  Therefore, the copper ions prefer to interact with the water, which is hydrophilic. “Like dissolves Like”

Conservation of Matter and Stoichiometry

3. The conservation of atoms in chemical reactions leads to the principle of conservation of matter and the ability to calculate the mass of products and reactants. As a basis for understanding this concept:

a. Students know how to describe chemical reactions by writing balanced equations.

    CuSO4(s) + H20(l) ‡ Cu2+(aq) + SO42-(aq)

d. Students know how to determine the molar mass of a molecule from its chemical formula and a table of atomic masses and how to convert the mass of a molecular substance to moles, number of particles, or volume of gas at standard temperature and pressure.

    Calculate the molar mass of CuSO4
Cu atomic weight = 63.546 g/ mol
S atomic weight = 32.05 g/ mol
O atomic weight = 15.9994 g/mol
CuSO4  = 159.59 g/mol 

Acids and Bases

5. Acids, bases, and salts are three classes of compounds that form ions in water solutions. As a basis for understanding this concept:
a. Students know the observable properties of acids, bases, and salt solutions.

A copper sulfate salt solution is prepared in water and the solution contains positive and negative ions.


6. Solutions are homogenous mixtures of two or more substances. As a basis for understanding
this concept:
a. Students know the definitions of solute and solvent.

For both solutions, water is the solvent and Yellow #6 and  CuSO4 are the solutes.  The zeolite and the activated carbon do not dissolve in the water and form suspensions, rather than solutions.

b. Students know how to describe the dissolving process at the molecular level by using the concept of random molecular motion.

    Students can describe the dissolution of  CuSO4 through this method.

c. Students know temperature, pressure, and surface area affect the dissolving process.

Large surface area of activated carbons and zeolites helps bind more dye molecules and copper ions, respectively.

d. Students know how to calculate the concentration of a solute in terms of grams per liter, molarity, parts per million, and percent composition.

    Can calculate the concentrations of the solutions

Reaction Rates

8. Chemical reaction rates depend on factors that influence the frequency of collision of reactant molecules. As a basis for understanding this concept:

a. Students know the rate of reaction is the decrease in concentration of reactants or the increase in concentration of products with time.

The zeolite mechanism of copper(II) ion removal is by exchanging Na+ ions for Cu2+ ions.  As copper (II) ions exchange into the zeolite the concentration of copper ions in the solution decreases (and when the zeolite is filtered from the solution, the color provided by the copper ions is removed).

b. Students know how reaction rates depend on such factors as concentration, temperature, and pressure.

    Heating and decreasing contaminates concentration will increase the reaction rate of filtration.

Earth Sciences

California Geology

9. The geology of California underlies the state’s wealth of natural resources as well as its natural hazards. As a basis for understanding this concept:

c. Students know the importance of water to society, the origins of California’s fresh water, and the relationship between supply and need.

    Water filtration is important part of providing fresh water to the state of California.

Investigation and Experimentation

1. Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and addressing the content in the other four strands, students should develop their own questions and perform investigations. Students will:

b. Identify and communicate sources of unavoidable experimental error.

c. Identify possible reasons for inconsistent results, such as sources of error or uncontrolled conditions.

d. Formulate explanations by using logic and evidence.