Chemical Changes Gizmo Answer Key

Name: Haley Spears Date: 04-23-2022 Chemical Changes Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes. Vocabulary: acid, base, catalyst, chemical change, coefficient, conservation of matter, decomposition, dissolve, double replacement, endothermic, exothermic, indicator, ion, physical change, product, reactant, single replacement, subscript, synthesis Prior Knowledge Questions (Do these BEFORE using the Gizmo.) 1. A student mixes baking soda and vinegar in a glass. The results are shown at left. Do you think any new substances are being created in this mixture? If so, how do you know? I think carbon dioxide is the material that emerged from the mixture. This is due to the fact that when vinegar and baking soda are combined, a gas is produced (carbon dioxide) 2. Suppose this was done on top of a balance. Do you think the mass would change as the reaction proceeded? If the gas is allowed to escape, the mass will decrease rather than remain constant. 3. What do you think would happen to the mass if the reaction took place inside a sealed plastic bag? Due to its concealment, the mass would remain unchanged. Gizmo Warm-up A chemical change, (or chemical reaction) occurs when one or more substances, called reactants, are transformed into different substances, or products. In the Chemical Changes Gizmo, you will look for evidence of chemical changes by looking at changes you can see, touch, or smell. To begin, check that Reactant 1 is Sodium and Reactant 2 is Water. Sodium is a metal so soft you can cut it with a knife. 1. Click Play ( ). What do you observe? The glass of sodium was removed, and the water was added. The sodium dispersed in the water, increasing the mass. 2. Do you think a chemical reaction has taken place? Explain. Yes, I do think that the gas discharged into the air caused a chemical reaction to occur. Get the Gizmo ready: Activity A: Observing chemical changes ● Click Reset ( ). Check that the reactants are still Sodium and Water. ● Turn on the Label reactants checkbox. Introduction: It is important to distinguish chemical changes, in which new substances are formed, from physical changes, which do not create new substances. In this activity, you will look at many kinds of evidence that chemists use to see if a chemical change has taken place. Question: What kinds of evidence indicate a chemical change has taken place? 1. Observe: Some chemical reactions release heat, and others absorb heat. In an exothermic reaction, heat is released and the temperature of the system rises. In an endothermic reaction, heat is absorbed and the temperature of the system decreases. In the Gizmo, drag the Thermometer into the flask of water. A. What is the starting temperature? 21 Celsius B. Click Play, and wait for the reaction to end. What is the final temperature? 59 Celsius C. Was this reaction exothermic or endothermic? Exothermic. 2. Observe: Two families of chemicals are acids and bases. Acids and bases can be detected by an indicator, which is a substance that changes color in the presence of an acid or a base. Phenol red is an indicator that is yellow in an acid, orange in a neutral solution, and pink in a base. A. Click Reset. Drag the Phenol red next to the flask of water. What does the indicator show? Start PH: Neutral, 423.0g mass. Orange Phenol. B. Click Play, and wait for the reaction to end. What does the indicator show now? PH: Basic, 422.9g mass, sodium dissolved, When the water from the sodium was added, phenol turned red or pink. 3. Observe: Click Reset. Select the Gas collection setup. Chemists use this apparatus to collect any gases produced in the reaction. From the reaction flask, gases travel through a long tube and into a cylinder of water. As gases bubble into the cylinder, the water is displaced (removed) until the cylinder is filled with gas. Click Play and observe the cylinder. Was any gas produced in the reaction? No How do you know? No gas was released; instead, bubbles appeared as a result of everything being sealed or closed off. 4. Analyze: 1. One way to test what kind of gas is in the cylinder is to use a splint test. A glowing splint is a wooden stick that has been lit on fire and then blown out, resulting in a glowing, red-hot tip. A burning splint is a splint that has a burning tip. The table shows how a splint reacts to some common gases: Gas Carbon dioxide (CO2) or ammonia (NH3) Oxygen (O2) Hydrogen (H2) Glowing splint Goes out Ignites (burns) Does not ignite Burning splint Goes out Continues to burn Small explosion and “pop” sound A. Drag the glowing splint next to the cylinder, and observe. What do you see? I don't notice any change. B. Click Reset and click Play, and then bring the burning splint to the cylinder. What happens now? The burning splint turns off. C. Based on the table above, what gas do you think was produced in this reaction? Hydrogen 5. Interpret: Turn on Show chemical equation. A chemical equation is a shorthand way to describe a chemical reaction. Symbols represent the elements: H for hydrogen, O for oxygen, and Na for sodium. The reactants are to the left of the arrow, and the products are to the right. For example, the equation H2 + O2 → H2O shows that the reactants hydrogen and oxygen combine to form the product H2O, or water. A. Look at the reaction shown in the Gizmo. What are the reactants in this reaction? 2Na+2H2O (sodium and water) B. What are the products in this reaction? 2NaOH+H2 (Holmium and Hydrogen) These symbols represent sodium hydroxide and hydrogen gas. Sodium hydroxide is a strong base. (Chemicals that contain the hydroxide ion (OH–) are bases.) C. How do the products of the reaction relate to the phenol red test and the splint test? Because it demonstrates a strong base and a reaction, the reaction's byproducts connect to the phenol red test and splint test. Activity B: Get the Gizmo ready: Conservation of matter ● Click Reset. Select Hydrogen peroxide for Reactant 1 and Potassium iodide for Reactant 2. Goal: How does the mass change (or not change) during a chemical reaction? 1. Review: In this reaction, hydrogen peroxide is added to a potassium iodide solution. Click Play and observe the reaction. A. What do you observe? When potassium iodide solution was combined with hydrogen peroxide, the solution's color changed and the water in the capsule was released. B. What evidence do you see that a chemical reaction is taking place? The potassium iodide solution's alteration in color. C. Replay the reaction and use the available tools (Thermometer, Phenol red, Glowing splint, Burning splint.) What do these tools indicate? (Note: You will need to switch to the Gas collection setup to use the splint.) Thermometer: 21 degrees in the beginning and 83 degrees at the end. Phenol red: Start PH: Neutral, End: PH Neutral, there was no change at all. Glowing splint: It begin burning Burning splint: Flamed remained light. 2. Record: Click Reset, and change back to the Normal setup. Notice the mass shown on the electronic balance. A. What is the starting mass for this reaction? 336.6g B. Click Play. What is the mass when the reaction has finished? 335.2g C. How does the mass change in this reaction? It decreases 3. Record: Click Reset, and select the Gas collection setup. Notice that this setup is heavier than the normal setup, but the amount of reactants is the same. A. What is the starting mass for this reaction? 2386.6g B. How do you think the mass will change during the reaction? Yes, I believe that during the reaction, the mass will change. It might decrease. C. Click Play. What is the mass when the reaction has finished? 2386.6g 4. Explain: Why do you think that mass was lost when the reaction was done in the normal setup, but stayed the same when the reaction was done in the gas collection setup? Due of the gas's ability to enter or exit the open container, the mass has changed. Because you have a closed system and nothing (gas) can escape or be added, the arrangement for collecting gas keeps its mass constant. A fundamental law of chemistry is conservation of matter. This law states that, in a chemical reaction, matter can neither be created nor destroyed. That means that, as long as nothing escapes from the system, the total mass measured at the start of the reaction will be the same as the total mass at the end of the reaction. 5. Compare: Turn on Show chemical equation. The small numbers, called subscripts, show how many of each atom there are in the molecule. For example, the molecule H2O contains two hydrogen atoms and one oxygen atom. (Notice that, in this reaction, the potassium iodide (KI) acts as a catalyst. A catalyst is a substance that helps a reaction happen but does not change during the reaction.) Count the total number of hydrogen and oxygen atoms on the left and right sides of the equation: Left side: H 2 O 2 Right side: H 2 O 3 What do you notice? KI is the catalyst. The equation is H2O twice and O twice. 6. Turn on Show balanced equation. A balanced equation shows how many molecules of each substance take part in the reaction. The coefficients are the big numbers that tell you how many molecules there are. For example, “2H2O” means there are two water molecules and a total of four hydrogen and two oxygen atoms. Carefully count the total number of hydrogen and oxygen atoms on the left and right sides of the balanced equation: Left side: H 4 O 4 Right side: H 4 O 4 A. What do you notice? The equation is balanced. B. How does the balanced equation relate to the law of conservation of matter? It pertains to the rule of conservation of matter because a chemical equation is balanced when the same amount of atoms of an element are present on both sides of the equation. Activity C: Types of reactions Get the Gizmo ready: ● Click Reset. Select Normal setup. ● Select Sodium for Reactant 1 and Chlorine for Reactant 2. Goal: Explore, observe, and classify a variety of chemical reactions. 1. Observe: In this reaction, a small piece of sodium is added to a flask containing poisonous chlorine gas which has a yellowish color, and sand. Water is added to start the reaction. A. Click Play. What happens? When sodium and water are combined to chlorine, the sodium burns up and withers away. The mass varies as well. It weighs 348.0g in the beginning and 351.1g at the conclusion. B. Try the experiment with the Thermometer. Is the reaction exothermic or endothermic? Begin 363.9g; End 366.1g. 21 degrees Celsius at start; >100 degrees Celsius at end. C. Run the experiment one more time, this time watching the mass. What do you notice? The mass grew from 363.9 g at the beginning to 366.1 g at the conclusion. D. Repeat the experiment, this time in the Closed system. How does the mass change during the reaction now? Beginning at 1351. 1g up to 1351. Mass of 1 g did not change. 2. Challenge: Turn on Show chemical equation. In this reaction, solid sodium reacts with chlorine gas to form solid sodium chloride (NaCl), also known as table salt. How does this explain the normal setup increase in mass during the reaction? The mass increases when testing a closed system. Both ions have entire valence shells and are energetically more stable when solid sodium combines with chloride gas. 3. Observe: Select Ammonium nitrate for Reactant 1 and Water for Reactant 2. Add the Thermometer to the flask and click Play. A. What do you observe? The temperature lowered because it was 21 degrees Celsius when it started and was only 13 degrees Celsius when it ended. B. Is this process exothermic or endothermic? endothermic C. What is the equation for this process? NH4NO3+H20->NH4++NO3-+H20 In this example, ammonium nitrate (NH4NO3) dissolves in water, producing ammonium (NH4+) and nitrate (NO3–) ions. Chemists do not all agree about whether this is an example of a physical change or a chemical change. 4. Classify: There are many types of chemical reactions. Four are described below: ● Synthesis: Two or more reactants combine to form a single product. For example, 2H2 + O2 → 2H2O. (Synthesis reactions are also called combination reactions.) ● Decomposition: One reactant breaks down to form two or more products. For example, 2KCl → 2K + Cl2. ● Single replacement: An element reacts with a compound to form another element and compound. For example, Zn + 2HCl → ZnCl2 + H2. ● Double replacement: Two compounds react to form two different compounds. For example, FeS + 2HCl → FeCl2 + H2S. Using the Gizmo, find an example of each type of reaction. Synthesis: Sodium and chlorine Decomposition: 2 hydrogen Single replacement: potassium + water => potassium hydroxide + hydrogen Double replacement: Sodium sulfide + 2 hydrogen chloride => 2 sodium chloride + hydrogen sulfide 5. Explore: Find an example of each of the following in the Gizmo: A. An example of no chemical reaction occurring: Hydrogen + helium B. A reaction that produces an acid: water + Hydrogen chloride = hydrochloric acid C. A reaction that produces a base: salt + water + electrons/electrolysis = sodium hydroxide D. A reaction that uses a catalyst: Iodine + fluorine = Iodine monofluoride (it requires water) 6. Demonstrate learning: Choose an interesting reaction in the Gizmo. Use the available tools to make observations, and use what you have learned so far to draw conclusions about the reaction. Describe your findings below. Reaction: silver nitrate + hydrochloric acid Findings: For a number of reasons, the double displacement reaction is a chemical reaction. There was a change in temperature first. This exothermic process causes the material to rise by one degree. Despite there being no gas emission, a white precipitate did form. Additionally, this reaction results in the production of an acid, which is visible after performing the phenol red test. This indicates that there aren't many hydrogen ions present in the substance.