Modeling the Atoms in the Chemical Reactions with the Element Cards Model the Atoms in the Chemical Reactions You Just Performed

UNIT 3 CHEMICAL REACTIONS L7ATOMS IN CHEMICAL REACTIONS

What happens to atoms during chemical reactions?

OBSERVING PHENOMENA

Carefully observe as your teacher places a piece of steel wool on a ceramic plate and places both on the digital balance so you can observe the mass of the steel wool. Your teacher lights the steel wool on fire. Note any patterns of change in mass as the steel wool burns. Consider if this could be related to structural changes at an atomic level. OBSERVING PHENOMENA

Phenomenon: Burning steel wool causes the mass of the steel wool to increase. What questions do you have about this phenomenon? Introduction A car sits in a field, rusting. Over time, the rust builds up thickly on the once-smooth steel parts of the car, parts containing iron. It seems to grow, as the rust gets thicker and thicker. The iron- containing parts get heavier and heavier, until the rust crumbles away, leaving jagged holes. What is happening here? Is matter disappearing or appearing? Although it may seem like matter is appearing out of nowhere as the rust grows, the extra mass comes from oxygen in the air. A chemical reaction has occurred in which atoms of iron and oxygen come together to form a new substance: iron oxide, or rust. You have already learned about substances and their properties. You also learned about chemical reactions and how to identify whether they have occurred by testing the properties of the substances. Now, you will explore what happens at the atomic level during chemical reactions. In this lesson, you will learn how atoms in chemical reactions regroup to form new substances. You will learn that the total number of atoms involved in a chemical reaction does not change. Thus, their total mass does not change either. Finally, you will learn how engineers use chemical reactions to make products in more environmentally friendly ways by analyzing the results of chemical reactions. Sec 1. Atoms Regroup in Chemical Reactions p106-107 Thinking of Atoms in Chemical Reactions • Chemical reactions occur when the bonds between atoms in the reactants break and reform to make new substances – the Products • The atoms that made up the molecules and extended structures of the reactants can form new molecules and extended structures in the products. Sec 1. Atoms Regroup in Chemical Reactions p106-107 A chemical reaction occurs when the bonds between the atoms of oxygen and hydrogen break within a water molecule. These atoms then form new bonds to produce oxygen gas and hydrogen gas. Atoms that are regrouping in this chemical reaction. Sec 1. Atoms Regroup in Chemical Reactions p106-107 When electric current passes through water, a reaction called electrolysis can take place. During the reaction, the bonds between the atoms of water molecules break and reform between pairs of hydrogen atoms or pairs of oxygen atoms.

The chemical reaction has produced the molecules of two different substances: O2 and H2. Since there are twice as many atoms of hydrogen as there are atoms of oxygen, the tube on the left, which contains hydrogen gas, contains twice as much gas as the tube on the right. Sec 1. Atoms Regroup in Chemical Reactions p106-107 Writing Chemical Reactions To describe how atoms regroup during reactions, scientists write equations using chemical formulas and element symbols. Chemical equations are shorthand notations that describe chemical reactions. Sec 1. Atoms Regroup in Chemical Reactions p106-107 Annotate the image with the following labels: • Reactants • Products • Chemical bond Then, in red, circle the chemical bonds that break. In blue, circle the chemical bonds that formed.

This is not really “your choice” I would like you to draw pictures of the atoms in the reaction and chemical Equation You may use examples in book or online Sec 2. Ways Atoms Regroup in Chemical Reactions p108-109 Molecules Break Apart Decomposition Reaction In some reactions, groups of atoms that make up one substance break apart. These atoms form new groups of atoms that make up two or more other substances. Sec 2. Ways Atoms Regroup in Chemical Reactions p108-109 Molecules Break Apart Decomposition Reaction In some reactions, groups of atoms that make up one substance break apart. These atoms form new groups of atoms that make up two or more other substances. Sec 2. Ways Atoms Regroup in Chemical Reactions p108-109 Atoms of Multiple Substances Combine Synthesis Reaction In some chemical reactions, the molecules or extended structures that make up two or more substances join together to form new groups of atoms that make up a single substance.

When atoms New chemical of iron and bonds form molecules of between the oxygen react, oxygen atoms the bonds and the iron between the atoms to make molecules of the extended oxygen structure iron break. oxide. Sec 2. Ways Atoms Regroup in Chemical Reactions p108-109 Atoms Switch Places Displacement Reaction In some chemical reactions, atoms within one group swap places with atoms within another group.

The lead atom swaps places with the potassium atoms to produce lead iodide and potassium nitrate.

3. Conservation of Matter

Scientists describe this idea in the law of conservation of matter, a scientific law that states that matter cannot be created or destroyed. This law means that matter is not created or destroyed during state changes, chemical reactions, or any other changes in matter.

A scientific law is a verbal or mathematical description of a natural phenomenon. For example, conservation of matter can be stated as: matter before reaction = matter after reaction

why the mass does not change in a chemical reaction between acetic acid (vinegar) and sodium bicarbonate (baking soda).

Since the atoms are neither created nor destroyed, the overall mass remains the same. The atoms have simply rearranged to form new substances. 3. Conservation of Matter 3. Conservation of Matter

Equations Model Conservation of Matter in Chemical Reactions In all chemical reactions, the atoms of the reactants regroup to form new combinations in the products. No matter how atoms rearrange, the number of atoms does not change. In most chemical reactions, atoms break apart and then join together, swapping places. This diagram shows the chemical reaction that occurs when someone takes an antacid for digestive pains.

3. Conservation of Matter No matter which way atoms regroup during a chemical reaction, atoms never appear out of or disappear into thin air. The law of conservation of matter states that matter cannot be created or destroyed during a chemical reaction. For example, when baking soda and vinegar are mixed, the reaction forms water, sodium acetate, and carbon dioxide. If you count the number of atoms in the reactants and the products, you will notice that they are the same before and after the reaction. Fill out the following table with the number of each element in the chemical reaction. Reactants Products

Acetic acid Sodium Sodium acetate Water Carbon dioxide bicarbonate

H (hydrogen)

C (Carbon)

O (Oxygen)

Na (Sodium)

Use the information in the table to explain why the mass does not change in a chemical reaction between acetic acid (vinegar) and sodium bicarbonate (baking soda). 3. Conservation of Matter

C2H4O2 + NaHCO3 → NaC2H3O3 + H2O + CO2 If you count all of the atoms, you will find that the number of atoms in the reactants (14) equals the number of atoms in the products (14).

INVESTIGATION 1 MODELING CHEMICAL REACTIONS

Think about what you observed when steel wool was burned. What patterns can you use to identify whether or not a chemical reaction has happened? The properties of the substances change since a new substance has formed. You could measure the properties of the substance each time it changes colors. INVESTIGATION 1 MODELING CHEMICAL REACTIONS

What is happening to the atoms during a chemical reaction? Atoms are so small that you cannot see how they interact using a conventional microscope. How can you possibly know what is going on if you cannot see it? You can use models.

INVESTIGATION 1 MODELING CHEMICAL REACTIONS

For each reaction, illustrate your model. Use circles of different colors to represent the different atoms and sticks to represent the bonds between the atoms. INVESTIGATION 1 MODELING CHEMICAL REACTIONS For each reaction, illustrate your model. Use circles of different colors to represent the different atoms and sticks to represent the bonds between the atoms. INVESTIGATION 1 MODELING CHEMICAL REACTIONS

Count the atoms before and after a chemical reaction. What do you notice? There is the same number of atoms & same types of elements before and after a chemical reaction. – They are just rearranged What do you notice happens to the chemical bonds between the atoms? Chemical bonds are broken and then reform between different atoms form different molecules and extended structures. What do you notice about the molecule size before and after a reaction? Molecules can get bigger or smaller depends on the number of atoms in the molecule INVESTIGATION 1 MODELING CHEMICAL REACTIONS Think back to the PhET simulation you worked with. What are the similarities and differences between the simulation and the Element Card model you used. INVESTIGATION 1 MODELING CHEMICAL REACTIONS Think back to the PhET simulation you worked with. What are the similarities and differences between the simulation and the Element Card model you used. Computer Simulation Element Cards INVESTIGATION 1 MODELING CHEMICAL REACTIONS

Wrap up Why do scientists use models to look at chemical reactions? Atoms are too small to be seen. So, models help people observe the atomic behavior during a chemical reaction. How can you use this model to predict how atoms in molecules and extended structures behave? This model demonstrates that the atoms separate and then reform in different groups and arrangements. So, you can predict that the products are made up of the same elements as the reactants.

Students perform three different chemical reactions. Measure the mass of substances before and after a chemical reaction has occurred. Use data to modify their explanations. Model the chemical reactions using element cards. INVESTIGATION 2 MEASURING THE MASS OF CHEMICAL REACTIONS

Discuss and answer questions #1-2 in your notebook 1) What changes during a chemical reaction? What stays the same? The bonds between the atoms and the atomic arrangement changes. The number and types of atoms stay the same. 2) Can you directly measure anything on the macroscopic scale to confirm that your model is accurate? You can measure the mass. You'll conduct three chemical reactions to see how accurate your predictions are. To confirm your predictions, you will need to measure the mass before and after the chemical reactions occur. INVESTIGATION 2 MEASURING THE MASS OF CHEMICAL REACTIONS INVESTIGATION 2 MEASURING THE MASS OF CHEMICAL REACTIONS

Change in Mass Cup Mass Reactant 1 Mass Reactant 2 Mass Product Mass (increase decrease (g) (g) (g) (g) or stay the same)

Reaction A: magnesium sulfate + sodium carbonate

Reaction B: sodium carbonate + calcium chloride

Reaction C: acetic acid + sodium bicarbonate INVESTIGATION 2 MEASURING THE MASS OF CHEMICAL REACTIONS Look closely at the data you gathered. In groups, discuss how the mass of the reactants compare to the mass of the products. You should use the words increase, decrease, or stay the same. 3) What did you notice from your data regarding mass of reactants and products? The mass either decreased (reaction 3) or stayed the same (reaction 1 and 2). 4) Does the data you gathered in this investigation support or refute the law of conservation of matter? The data refutes the law because it shows that sometimes the mass stays the same and other times the mass decreases. INVESTIGATION 2 MEASURING THE MASS OF CHEMICAL REACTIONS Modeling the Atoms in the Chemical Reactions With the element cards model the atoms in the chemical reactions you just performed. Reaction A magnesium sulfate + sodium carbonate → sodium sulfate + magnesium carbonate

MgSO4 + Na2CO3 → Na2SO4 + MgCO3 Reaction B sodium carbonate + calcium chloride → sodium chloride + calcium carbonate

Na2CO3 + CaCl2 → 2NaCl + CaCO3 Reaction C acetic acid + sodium bicarbonate → sodium acetate + water + carbon dioxide

C2H4O2 + NaHCO3 → NaC2H3O2 + H2O + CO2 INVESTIGATION 2 MEASURING THE MASS OF CHEMICAL REACTIONS INVESTIGATION 2 MEASURING THE MASS OF CHEMICAL REACTIONS INVESTIGATION 2 MEASURING THE MASS OF CHEMICAL REACTIONS INVESTIGATION 2 MEASURING THE MASS OF CHEMICAL REACTIONS 5) What did you notice about the atoms each reaction using element cards? How do they relate to the law of conservation of matter? Atoms of the reactants equal the atoms of the products All of the atoms are conserved. 6) There is an inconsistency between the results you got from your test, and the model you used. Describe the inconsistency. The results showed the mass decreasing when baking soda is mixed with vinegar. However, in the model, none of the atoms disappear. Why do you think the mass decreased in the chemical reaction between sodium bicarbonate and acetic acid? Some of the atoms formed a gas (carbon dioxide), which mixed with the air. (The gas escaped.) 7) How can redesign Reaction C of the experiment to resolve this inconsistency? You can try to capture the gas using a balloon

4. Engineering Green Medicines

Scientists perform chemical reactions to create medicines, but these chemical reactions can be inefficient. These reactions can also create waste products, which are reactants that did not react or products that are not desired.

The U.S. government started the Green Chemistry Program to develop more environmentally-friendly chemical processes and to reduce waste products. How? One criteria for a green engineering solution is that it makes processes more efficient. An efficient process is one in which most of the reactants become the desired products and less waste is produced. This criteria is found by measuring the mass of the reactants and products and then calculating the percentage of those substances that becomes a desired product. 4. Engineering Green Medicines

Beginning in the 1960s, industries used a very inefficient process to make ibuprofen, a painkiller and fever reducer. The process involved six different chemical reactions and produced large amounts of waste products. This process was 40% efficient, so less than half of the reactants' weight ended up in the desired product: ibuprofen. Over half of the reactant's mass became waste products. 4. Engineering Green Medicines

Reducing the Number of Reactions In the 1990s, a company decided to come up with a solution to maximize efficiency of the ibuprofen manufacturing process. Scientists at the company saw that they could use catalysts to make the process more efficient. Catalysts are substances that take part in a reaction but are not used up by the reaction. They help the reaction occur. They can be used again and again, so they do not become waste products after one use. 4. Engineering Green Medicines

Reducing the Number of Reactions Engineers researched chemical reactions that used catalysts to produce ibuprofen. Using these catalysts meant the process took 3 reactions instead of 6. A process with fewer chemical reactions has fewer reactants and therefore produces less waste products. It also saves time and is cost-efficient. After making this change, the reaction had an efficiency of 77 percent. This is a huge improvement from 40 percent— almost double the efficiency! The process better met their criterion. 4. Engineering Green Medicines

Reducing the Number of Reactions However, the scientists were not satisfied. They wanted to be able to come up with a way to make their reaction process more environmentally friendly. They wanted solutions that were even more efficient. 4. Engineering Green Medicines Using Products in Other Reactions For their second solution, the scientists looked for what waste product was being produced. One chemical reaction in their process produced acetic acid, which is the substance that gives vinegar its sour taste. When making ibuprofen, acetic acid was not considered a desired product, so it was thrown away as waste. To improve its efficiency, the scientists decided they would collect the acetic acid instead. They could use it as a reactant in other chemical reactions to make polyvinyl alcohol, which is used in eye drops and play putty. By reusing a waste product, they improved the efficiency of their process. 4. Engineering Green Medicines

Combining the Solutions Each of these two solutions would have improved the efficiency on their own. However, by combining them, they developed a process that was 99 percent efficient. This means that almost every single atom of reactants was in a desired product. This ibuprofen manufacturing process was so environmentally friendly that it won multiple chemical engineering awards! By analyzing their data and combining the best characteristics of two different solutions, the engineers developed a solution that better met their criteria. 4. Engineering Green Medicines

1. Describe the green method of ibuprofen production and how this solved the problem of an inefficient process. In the green method, scientists used catalysts to make the process more efficient. Because catalysts are not used up by the reaction, they can be used again and again without becoming waste products. This reduced the number of chemical reactions. As a result, ibuprofen production with the green method had an efficiency of 77%. 2. Describe the method of using products in other reactions and how this solved the problem of an inefficient process. Waste products of one chemical reaction can be useful reactants for different chemical reactions. By recycling waste products, the substance that was originally thrown away as waste becomes useful and increases the efficiency of a chemical reaction. 3. Describe how combining the two reactions helped solve the problem of an inefficient process. By combining both solutions, the process became extremely efficient. (99%) This is because each solution helps improve the efficiency on its own but combining the two results is a much better solution. 4. Engineering Green Medicines