Prescriptive Activities - Changes That Result in New Substances

Prescriptive activities may be assigned to individual students or to the whole class. These activities are designed to target specific problematic ideas diagnosed in the DIAGNOSER. They may be an extension of the developmental lessons and may include references to commercially (or freely) available curriculum. These activities can also be accessed from the teacher reports.

Scroll down or link to the facet: 70 80 90

Description of Changes That Result in New Substances Facet 70

(back to the top)
The student does not understand the relationships between various chemical representations (e.g. models, drawings, equations) of chemical reactions.
  • The student does not understand how to represent a chemical reaction to account for the fact that atoms are conserved.
  • The student thinks that the coefficient in front of the formula for the substance represents something other than the relative amount of each of the reactants and products.
  • The student does not understand how to determine the number of particles of each of the reactants and products in a chemical reaction.
  • The student does not know how to represent the particle interactions of a balanced chemical equation.
  • The student believes that if the reaction is not balanced, it will not occur.
  • The student views reactants and products as being in different locations in space rather than changes over time.
Most Common Conditions Where Facet 70 Occurs:

PA 70-75

Click Here for PDF Version of PA 70-75 (application/force-download, 476.9 kB, info)

Prescriptive #70-75:

70 The student does not understand the relationships between various chemical representations (e.g. models, drawings, equations) of chemical reactions.

71 The student does not understand how to represent a chemical reaction to account for the fact that atoms are conserved.

72 The student thinks that the coefficient in front of the formula for the substance represents something other than the relative amount of each of the reactants and products.

73 The student does not understand how to determine the number of particles of each of the reactants and products in a chemical reaction. (The total number of particles for each element can be calculated by multiplying the coefficient by the subscript.)

74 The student does not know how to represent the particle interactions of a balanced chemical equation.

75 The student believes that if the reaction is not balanced, it will not occur.

PA 76

Click Here for PDF Version of PA 76 (application/force-download, 390.2 kB, info)

Prescriptive #76:

The student views reactants and products as being in different locations in space rather than changes over time

Activity to address Facet 70:

PA 70-75

Background

Chemical reactions happen all around us, when you light a match, or eat dinner, there are chemical reactions that takes place. Any process that creates a new substance through changes in bond formation can be considered a chemical reaction. Chemical reactions often produce observable changes that indicate changes in bonds among atoms have occurred. However, the particles involved are too small to see. To understand and explain chemistry we have to find ways to represent the chemical reaction at a molecular level.

The shorthand way to describe a chemical reaction is to write it as a chemical equation.  For example, the following is a description of a chemical reaction.

Sodium oxide (in water) reacts with copper (II) chloride (in water) to form copper (II) oxide (a solid precipitate) and sodium chloride (in water).

The shorthand equation would be:

Na2O (aq) + CuCl2 (aq) => CuO(s) + 2NaCl (aq)

The subscript numbers within a chemical formula indicate how many of each kind of atom are bonded within the particles. In the example above, there are 2 sodium atoms attached to an oxygen atom.

The (aq) indicates that those substances are dissolved in water. They are aqueous solutions.

Notice that reactants have rearranged to form products but that mass has been conserved. That is there are the same numbers of atoms on each side of the arrow.

Purpose

This activity allows students to use models to demonstrate the conservation of atoms in a chemical equation and to use models to learn how to balance equations.

Materials:

  • Student handout
  • Scissors
  • Glue or tape

Directions of Activity:

Building paper atoms and molecules to show how they rearrange in chemical reactions.

1. Cut out the shapes on the back page. Each shape will represent a type of atom or molecule.

  • Triangles for the metals
  • Squares for the nonmetals
  • Star shapes for the polyatomic ions because they have two parts.

Here is a table of common polyatomic ions to refer to

Screen shot 2012-09-27 at 4.37.02 PM

2. Choose the correct shapes to represent the chemicals in each reaction below. Writethe correct symbol on each shape and put the shapes together to model the reactions.Remember, if you have two atoms in the reactants, the same two atoms must show up in the products.Matter is conserved in a chemical reaction.Remember, that to show a molecule, the atoms must be touching.

Screen shot 2012-09-27 at 4.37.44 PM

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Screen shot 2012-09-27 at 4.38.47 PM

Questions:

1.In number 10, how many particles of sodium phosphate are shown in the equation?

2.How many atoms of sodium participate in the reaction?

3.Would you ever see a balanced chemical equation with different numbers of atoms on either side of the arrow? Why or why not?

4.If you had the atoms represented in the image below in a container, would a reaction occur?

Screen shot 2012-09-27 at 4.38.54 PM

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______________________________________________________________________________________________________________

PA 76

Background:

The way that we write chemical reactions is sometimes interpreted to mean that the reactants exist in one location while the products exist in a different location. In reality, the reactant particles simply convert into the product molecules by rearrangement of their constituent atoms within the same location.

NaOH(s) + HCl(aq) => NaCl(aq) + H2O(l)

To carry out the reaction shown above, you would place solid NaOH pellets in a beaker containing HCl dissolved in water, and within the beaker the atoms would rearrange themselves to form the products: NaCl evenly dispersed throughout the solution and new liquid water molecules.

Shown below is a beaker with a mixture of chemicals shown at 4 different times during the reaction. Note that all the reactants and all the products are in the same beaker.

Screen shot 2012-09-27 at 4.45.19 PM

Video located at: http://www.techeblog.com/index.php/tech-gadget/video-briggs-rauscher-oscillating-color-change-reaction

Materials:

Student handout

A candle

Jar or beaker (tall enough to cover the burning candle)

Directions of Activity:

Light a candle. Place a jar or beaker over the burning candle and observe.

Questions:

1. Describe the appearance of the candle before burning.

2. The equation for the burning of the candle is given below. Circle the reactants in the equation for this combustion reaction.

3. Draw a box around the products in the equation.

4. Draw arrows showing where each of the substances is located in the picture below.

Screen shot 2012-09-27 at 4.45.58 PM

Screen shot 2012-09-27 at 4.46.22 PM

Resource For Facet 70:

PA 70-75

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PA 76

Teacher Notes

The Briggs-Rauscher Reaction

IO3- + 2 H2O2 + CH2(CO2H)2 + H+ à ICH(CO2H)2 + 2 O2 + 3 H2O

(from http://chemistry.about.com/cs/demonstrations/a/aa050204a.htm)


Description of Changes That Result in New Substances Facet 80

(back to the top)
The student doesn't understand that when the atoms of the reactants are rearranged to produce products, a new substance is produced with different chemical and physical properties. (Note: These PFs may occur once students are learning about chemical reactions, because they have no prior knowledge of the concepts. These may not be PFs that exist before instruction).
  • The student doesn't understand that the new substance (products) has different physical properties from the reactants.
  • The student doesn't understand that the new substance (products) has different chemical properties from the reactants.
  • The student thinks that a chemical reaction will not occur unless a phase change has occurred (eg. during a double-replacement reaction, if they see no precipitate or gas evolution no reaction has occurred).
  • The student believes once oxygen combines with something, it can never be oxygen by itself again.
  • The student does not recognize oxygen as a reactant in an open system oxidation reaction (i.e. rusting = loss of matter).
  • The student assumes that atoms can rearrange themselves without breaking bonds (eg. oxygen is accessible from compounds like CO2 without having to break CO2 bonds.
  • The student thinks that a chemical reaction is a phase change.
Most Common Conditions Where Facet 80 Occurs:

PA 80-83

Click Here for PDF Version of PA 80-83 (application/force-download, 183.5 kB, info)

Prescriptive:

80 The student doesn't understand that when the atoms of the reactants are rearranged to produce products, a new substance is produced with different chemical and physical properties. (Note: These PFs may occur once students are learning about chemical reactions, because they have no prior knowledge of the concepts. These may not be PFs that exist before instruction)
81 The student doesn't understand that the new substance (products) has different physical properties from the reactants.
82 The student doesn't understand that the new substance (products) has different chemical properties from the reactants.
83 The student thinks that a chemical reaction will not occur unless a phase change has occurred (eg. during a double-replacement reaction, if they see no precipitate or gas evolution no reaction has occurred).

PA 84

Click Here for PDF Version of PA 84 (application/force-download, 469.4 kB, info)

Prescriptive #84:

84 The student believes once oxygen combines with something, it can never be oxygen by itself again.

PA 85

Click Here for PDF Version of PA 85 (application/force-download, 150.6 kB, info)

Prescriptive#: 85

85 The student does not recognize oxygen as a reactant in an open system oxidation reaction

PA 86

Click Here for PDF Version of PA 86 (application/force-download, 452.7 kB, info)

Prescriptive#86:

86 The student assumes that atoms can rearrange themselves without breaking bonds (eg. Oxygen is accessible from compounds like CO2 without having to break CO2 bonds)

Activity to address Facet 80:

PA 80-83

Purpose

Observe and test physical and chemical properties of products and reactants in chemical reactions through mixing solutions

Materials:

Student handout

Equipment

Chemical solutions

6 small test tubes, test tube rack

0.1 M Silver nitrate (AgNO3)

6 small-scale pipets (one for each solution and one for stirring)

0.1 M Sodium hydroxide (NaOH)

6 pieces of litmus paper

0.1 M Iron nitrate (Fe(NO3)3)

0.1 M Calcium chloride (CaCl2)

0.1 M Sodium Carbonate (Na2CO3)

Directions for Activity:

Safety note: Handle chemicals with caution; NaOH is caustic – avoid contact with skin; AgNO3 will stain skin black.

  1. Put one drop of CaCl2 into 3 labeled test tubes.
  2. Add one drop of AgNO3 into test tube 1, one drop of Na2CO3 in test tube 2 and one drop of NaOH in test tube 3. Stir each with a clean stirring rod or toothpick.
  3. Observe and record any changes in appearance or texture (a physical property) in the chart below.
  4. Repeat Steps 1 and 2, using Fe(NO3)3 instead of CaCl2.
  5. Use litmus paper to test each test tube’s pH (a chemical property) both BEFORE and AFTER adding reactants. Record the pH values in the chart below.
  6. Cleanup and dispose of test tube contents

Screen shot 2012-09-27 at 4.51.29 PM

Questions

  1. When a chemical reaction occurs, the appearance may or may not change. Sometimes the color changes, sometimes a precipitate forms, and sometimes there is a change in texture or clarity. What physical changes did you observe for each reaction?
  1. Which mixtures gave no visible reaction? If no visible reaction took place, does that mean no reaction occurred?
  1. When a chemical reaction occurs, the chemical properties of the products are often different than the chemical properties of the reactants. List 5 different types of chemical properties.
  1. In which mixtures did you detect a pH change using litmus paper?
  1. Which mixtures did not undergo a chemical reaction? How do you know?

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PA 84

Materials:

Student handout

The story of oxygen:

We rely on oxygen for our very existence. We take oxygen for granted despite the fact that it has not always existed as an abundant atmospheric gas here on earth. For the first 2 billion years of earth’s 4.6 billion year history, there was virtually no atmospheric oxygen. The atmosphere consisted of methane (CH4), ammonia (NH3), hydrogen (H2) and carbon dioxide (CO2), collectively referred to as the primordial soup. The hydrogen gas, being very light, escaped into space. Any free oxygen quickly reacted with free iron in the earth’s oceans creating iron oxides which became buried deep in the earth over hundreds of millions of years. In the early history of earth, amino acids, nucleotides, sugars and fatty acids formed from the primordial soup, and later RNA and DNA formed, and simple chemical processes that form the basis of life began. Free oxygen is highly toxic to just about every part and process of living cells, and eventually a symbiotic relationship between early cells and protective mechanisms began. Chloroplasts and mitochondria as well as the mechanisms for shuttling oxygen into and out of the cell are the only things protected from oxygen’s toxicity. It is fortunate that there was no atmospheric oxygen in the early part of the earth’s history because life on earth may never have begun if there had been.

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Light from the Sun broke down the ammonia molecules released by volcanos, releasing nitrogen into the atmosphere. Over billions of years, the quantity of nitrogen built up to the levels we see today.

Although life formed just a few hundred million years after the earth formed, it wasn’t until the evolution of bacteria 3.3 billion years ago that the early Earth atmosphere really changed into the one we know today. By 2.7 billion years ago early bacteria, known as cyanobacteria, used energy from the Sun for photosynthesis, allowing cells to obtain carbon (C) from carbon dioxide (CO2) and hydrogen (H2) from water (H2O). Much of the bound oxygen was released as a byproduct, yet it wasn’t for another few hundred million more years that there was a dramatic increase in atmospheric oxygen levels. Scientists are still trying to figure out the details of how this increase occurred. One important aspect was that there was a decrease in the amount of hydrogen gas in the atmosphere, so any free oxygen would not be immediately taken up by hydrogen. Then, the O2 level increased. This increase resulted in an increase in iron oxides on in the earth’s oceans. At left is a picture of a “banded iron” rock which shows alternating layers of iron-rich (red) and iron-poor (gray) sediments. Eventually the increased oxygen levels used up all the free iron, and it was at this point that the O2 levels in the atmosphere really increased. 

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In just a few hundred million years, early bacteria completely changed the Earth’s atmosphere composition, bringing us to our current mixture of 21% oxygen and 78% nitrogen.

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Before this all happened, the amount of oxygen in Earth's atmosphere was about one ten-quadrillionth of the amount present today. Oxygen now makes up nearly 21 percent of Earth's atmosphere; most of the rest is nitrogen. The free oxygen gas was produced by plants when photosynthesis reactions released the oxygen from water.

The history of oxygen on earth shows on the grandest scale that oxygen can be released from elements to which it is bound in even the most stable compounds such as water and carbon dioxide. Today photosynthesis is a crucial part of the cycle by which oxygen is released into the atmosphere, thereby making it available to breathe in for all animals, including humans.

Questions:

1. In photosynthesis, plants take in carbon dioxide and water, and use these to build sugars (C6H12O6), releasing oxygen gas as a byproduct. Write the equation for photosynthesis.

2. Write the equation for respiration, in which results in sugar effectively being combined with oxygen, producing carbon dioxide and water.

3. Which one releases oxygen into the atmosphere? Where did the oxygen come from?

4. When you decompose hydrogen peroxide, it releases oxygen as bubbles. Where did the oxygen come from?

5. Oxygen is found in nature bonded to many different elements including carbon and hydrogen. How can this oxygen be released?

6. Provide your own explanation for the concept of the reversibility of chemical reactions?

Resources:

http://www.bettykamen.com/rice/History.html

http://www.universetoday.com/10932/early-atmosphere-looked-very-different-from-today/

http://iridiumminer.blogspot.com/2011/01/banded-iron-formations-clues-to-early.html

Earth’s Early Atmosphere image taken from: http://forces.si.edu/atmosphere/04_00_03.html

DNA and Cell picture taken from: http://www.koshland-science-museum.org/exhibitdna/intro02.jsp

http://iridiumminer.blogspot.com/2011/01/banded-iron-formations-clues-to-early.html

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PA 85

Purpose

The purpose of this activity is to observe a chemical reaction in an open oxidation system.

Materials:

  • Student handout
  • Candle (C25H52) (if candle cannot stand on its own, use a candle holder)
  • Matches
  • Glass (must fit over candle, a beaker works best)
  • Dish (a pie tin works well)

Directions for Activity:

1. Fill dish less than half full with water

2. Place candle in center of dish

3. Check that the glass fits over the candle and observe where the water rises to on the glass

4. Light the candle and place the glass over it

5. Observe changes in the water level in the glass

6. Note how long the candle burns

Questions

1. What happens to the water level in the glass once the candle starts burning?

2. For how long does the candle burn?

3. Draw a representation at the molecular level of what is under the glass before burning begins.

FC 2.3 PA 85 Open Oxidation system Teacher Version

4. How does your representation in #3 change as the candle burns? Illustrate this below.

Screen shot 2012-09-27 at 5.00.43 PM

5. Which reactant got used up thereby stopping the combustion reaction?

6. Write the chemical equation for this combustion reaction.

7. Another example where atmospheric oxygen is a reactant is in the rusting of iron (Fe) to produce iron (III) oxide (Fe2O3). Write a balanced chemical equation for this reaction. 

8. Provide another example of something reacting with atmospheric oxygen.

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PA 86

Materials:

  • Student handout
  • Marshmallows (3 different colors and sizes)
  • Toothpicks

Directions for Activity

For each reaction below:

  1. Write the balanced equation
  2. Select a marshmallow type to represent each element
  3. Build the reactant molecules using toothpicks and sketch them under the balanced equation.
  4. Using only the reactant molecules, reassemble the atoms to create the products. (More or less toothpicks may be used.)
  5. Sketch the product molecules under the balanced equation

Reactions

1. Hydrogen gas (H2) and chloride (Cl2) react to form hydrochloric acid (HCl).

Balanced equation:

Screen shot 2012-09-27 at 5.03.08 PM

2. Magnesium (Mg) and carbon dioxide (CO2) react to form magnesium oxide (MgO) and pure carbon (C).  Recall that CO2 has two double bonds as shown here. These can be represented by PAIRS of toothpicks: O=C=O.

Balanced equation:

Screen shot 2012-09-27 at 5.03.52 PM

Questions

1. Were you able to assemble the products using only the reactant atoms?

2. What must happen to reactant molecules before product molecules can be “built” in a chemical reaction?

Resource For Facet 80:

PA 80-83

Screen shot 2012-09-27 at 4.52.38 PM

PA 86

Teacher notes

Here is an example of a water molecule built of marshmallows and toothpicks. For this activity we recommend different colored marshmallows to more accurately represent the different atoms. For best results, have at least 3 types (color or size) of marshmallows. Small marshmallows can still be used to represent hydrogen.

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Note about ionic crystal structure:

You may want to remind students that ionic compounds actually form large repeating crystal lattices, and that the MgO that they build are the simplest representation of the ratio and arrangement of atoms within the crystal.

Answer Key

H2 + Cl2 =>2HCl

2Mg + CO2 => 2MgO + C


Description of Changes That Result in New Substances Facet 90

(back to the top)
The student thinks that atoms of the reactants get lost or that new atoms are added to the atoms of the products in a chemical reaction.
  • The student thinks that atoms come from some place other than the reactants in a chemical reaction.
  • The student thinks that atoms of the reactants can disappear in a chemical reaction.
  • The student believes atoms of one element change into atoms of a different element in a chemical reaction.
  • The student thinks that burning a substance turns that substance into energy and left over pieces of the substance.
  • The student believes when gas is produced, the reaction has lost mass.
  • The student cannot identify all of the reactants or all of the products of a chemical reaction, so does not know how to correctly predict the conservation of mass.
Most Common Conditions Where Facet 90 Occurs:

PA 90-93

Click Here for PDF Version of PA 90-93 (application/force-download, 192.2 kB, info)

Prescriptive#: 90-93

90 The student thinks that atoms of the reactants get lost or that new atoms are added to the atoms of the products in a chemical reaction.

91 The student thinks that atoms come from some place other than the reactants in a chemical reaction.

92 The student thinks that atoms of the reactants can disappear in a chemical reaction.

PA 94

Click Here for PDF Version of PA 94 (application/force-download, 87.7 kB, info)

Prescriptive#:

94 The student thinks that burning a substance turns that substance into energy and left over pieces of the substance.

PA 95

Click Here for PDF Version of PA 95 (application/force-download, 159.1 kB, info)

Prescriptive#: 95

95 The student believes when gas is produced, the reaction has lost mass.

Activity to address Facet 90:

PA 90-93

Materials:

  • Student handout
  • Flask and stopper
  • Potassium hydroxide (KOH)
  • Glucose
  • Ice

Directions for Activity:

Safety: Potassium hydroxide is corrosive; contact with skin causes severe blisters

1. Add about 8 g KOH to 300 ml of water in a flask.

2. Cool the solution and dissolve about 10 g of glucose in it.

3. Add 2-3 drops of methylene blue indicator.

4. Stopper the flask, shake and swirl. Record your observations.

5. Let the flask sit undisturbed for 5 minutes. Record your observations.

6. Swirl the flask and record your observations.

Questions

1. Oxygen is involved in this chemical reaction. Where do you think oxygen is within this system when the flask is sitting still?

2. What happens to the oxygen when you shake the flask?

3. Where are the products in this reaction?

4. When the solution turns from blue to colorless, where do you think the oxygen goes?

5. Illustrate where you think the reactants (oxygen and methylene blue) and products (oxidized methylene blue) are in this reaction when it is blue and when it is colorless.

Screen shot 2012-09-27 at 5.17.54 PM

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PA 94

Materials:

Student handout

Directions for Activity:

Refer back to the developmental lesson on Burning magnesium.

Questions

1. What happened to the mass when the magnesium burned?

2. Provide an explanation for this observation.

3. The chemical equation for this reaction is given below.

2 Mg (s) + O2 (g) => 2 MgO (s)

What bonds had to break in order for the reaction to take place?

4. Draw the reactant atoms at the particle level before the reaction occurred.

Screen shot 2012-09-27 at 5.20.09 PM

5. Why does the magnesium not spontaneously combust when it is sitting in the room?

6. What bonds formed as the reactant atoms were rearranged into the product?

7. How do you know that this reaction released energy?

8. Where do you think the energy came from?

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PA 95

Materials:

  • Student handout
  • Alka-seltzer
  • Vinegar
  • Balloon
  • Flask

Directions for Activity:

1. Place an Alka Seltzer in a balloon.

2. Put some vinegar in the flask

3. Weigh the balloon, alka seltzer, flask and vinegar all together

4. Put the neck of the balloon completely around the flask opening and get the Alka Seltzer to fall into the flask

5. Observe

6. Weight the whole system

Questions

1. Describe your observations when the Alka Seltzer fell into the vinegar?

2. Draw and label a representation of the particles within the flask and the balloon both before and after the reaction occurred.

Screen shot 2012-09-27 at 5.23.15 PM

3. What was in the balloon after the reaction occurred?

4. What happened to the mass of the system?

5. Does the gas in the balloon have mass? How can you tell?

6. This reaction occurs in a closed system, meaning that the reactants and products are all within a contained space. Particles cannot enter from the surroundings and cannot leave (unless some small particles escape through the tiny holes in the balloon). Why is it often difficult to measure the mass of the products for a reaction that is open to the surroundings?

7. How did this activity attempt to address this difficulty?

Resource For Facet 90:

PA 90-93

Teacher Notes:

You can prepare the solution ahead of time and give student groups a small stoppered flask with some solution in it.

Chemical reactions involved:

When shaken:

O2 + methylene bluereduced à methylene blueoxidized

Upon standing:

RH + OH- => R- + H2O (R = glucose)

Methylene blueoxidized + R- => methylene bluereduced + glucose oxidation products

The process of shaking to turn blue can be repeated about 10 times before the glucose gets used up.

Disposal:

Neutralize the resulting solution according to Flinn Suggested Disposal Method #10 for Bases, Strong and Weak, and Basic Anhydrides. Bases should be neutralized by a mild process of diluting to 1 M or 10% and neutralizing with dilute hydrochloric acid to pH of 5-9 before discharge to the drain. The procedure can be found in the current Flinn Chemical Catalog/Reference Manual