How do you know when a new substance forms? Observing the Phenomena Observe the Vinegar – Write down ALL characteristics/properties Observe the Baking Soda – write down ALL characteristics/properties Follow teacher directions – write down ALL changes/observations during and after Observing the Phenomena Watch as your teacher conducts this demonstration. How is the resulting gas different than the ingredients that produced it? Observing the Phenomena Phenomenon: Mixing vinegar and baking soda causes the substances to bubble up and spill over a container’s edge. What questions do you have about this phenomenon? Introduction p91 In a lab, a scientist has two clear liquids. The scientist slowly mixes the two together. The minute they touch, a bright yellow material forms. It swirls through the liquid before settling into solid clumps. What just happened? A new substance formed in this chemical reaction. Chemical reactions occur all around you, such as when you cook food or burn wood. Many of the changes in matter that you see around you each day are a result of chemical reactions forming new substances. How do you know when a chemical reaction is happening? You cannot always tell a chemical reaction has happened by looking. Instead, you have to understand what is happening on the atomic level. Recall that you can “see” atoms using a Scanning Tunneling Microscope. But if you did not have a Scanning Tunneling Microscope, how could you determine if a chemical reaction occurred? In this lesson, you will learn how chemical reactions change one or more chemical substances. Your observations of changes can provide evidence as to whether a chemical reaction has taken place. These changes can be noticed by observing the properties of newly formed substances and comparing them to the properties of starting substances. You will also learn how scientists use chemical reactions to develop modern medicines. 1. Chemical Reactions Change Substances (p92) This kind of change is a chemical reaction, a process in which one or more new substances are formed from one or more other substances. Substances that exist before a chemical reaction takes place and change as a result of the reaction are called reactants. New substances that form in chemical reactions are called products. In a chemical reaction, reactants react to produce Reactants change to products. form products that have Products are different substances than the entirely different reactants from which they came. properties. 1. Chemical Reactions Change Substances (p92) Products have a different set of properties than the reactants. Properties of matter are only noticeable during or after a chemical reaction. https://suite.smarttech.com/student/share/1eb50a10-aa75-417f-9639-7d71299c2954 1. Chemical Reactions Change Substances (p92) Lead Nitrate + Potassium Iodide → Lead Iodide + Potassium Nitrate Both white solids Potassium Nitrate that dissolve in and white solid water dissolved in water Colorless mixtures Lead Iodide: yellow solid not soluble in water Products have a different set of properties than the reactants. 1. Chemical Reactions Change Substances 1. What is a chemical reaction? A process in which one or more substances are formed from one or more other substances. 2. Why isn’t a state change from liquid to solid a chemical reaction? A substance can exist in more than one state—water that freezes to ice is still the same substance. No New Substance is formed 3. When lead nitrate and potassium iodide are mixed, lead iodide and potassium nitrate form. What are the reactants and products in this chemical reaction? Reactants: lead nitrate and potassium iodide Products: lead iodide and potassium nitrate (yellow solid) (clear liquid) 4. What is the difference between chemical properties and physical properties? Chemical properties are only noticeable during or after a chemical reaction. All other properties are physical properties. 2. Conditions that Cause Chemical Reactions Observe a match as it is struck. The substances in a match undergo a chemical reaction that produces a bright hot flame. Whether a reaction happens depends on the chemical properties of the reactants and on the specific conditions they are under. Different conditions can cause different reactants to undergo chemical reactions. 2. Conditions that Cause Chemical Reactions 2. Conditions that Cause Chemical Reactions 2. Conditions that Cause Chemical Reactions 2. Conditions that Cause Chemical Reactions 1. Why don’t matches catch on fire while they are in the box? The reactants need some energy to interact, which occurs with the friction (causes heat energy) of striking the match. 2. What are three conditions that can cause chemical reactions to occur? Heating, cooling, and mixing 3. Give an example of a chemical reaction that is caused when reactants cool. When cooled, nitrogen dioxide goes through a chemical reaction and forms dinitrogen tetroxide. 4. Give an example of a chemical reaction that is caused when reactants are mixed. When mixed, acetic acid and sodium bicarbonate go through a chemical reaction and form carbon dioxide and some other materials. 3. Evidence of Chemical Reactions p96-97 Scientists collect data to use as evidence of a chemical reaction. Scientific evidence is data that can be used to support a claim or argument. Change in the property of color is a clue a new substance is forming. New substances form during chemical reactions. Products will have properties that differ from those of the reactants. Scientists collect data on the properties of reactants and products to identify changes between them. They measure properties of reactants and products and compare whether they are different. This data is evidence of a chemical reaction. 3. Evidence of Chemical Reactions Change in Odor p96-97 Change in Color “Characteristic" Properties Change Evidence of a Chemical Reaction Gas is Change in IF 2 or more Produced Energy changes occur than we know there is a Precipitate NEW substance can Form being formed Part 1 – Sodium Carbonate plus Hydrochloric Acid Hydrochloric Acid + Sodium Carbonate (powder) 1) Put 1 small spoonful of Sodium Part 1 2HCl + Na2CO3 2NaCl + CO2 + H2O Carbonate onto a clean/dry watch glass. 2) Record the appearance of the sodium HCl Observations carbonate in the data table. before 3) Observe a dropper containing Na2CO3 reaction hydrochloric acid. CAUTION: Hydrochloric acid can burn you and/or Observations anything else it touches. Wash spills during reaction with water. 4) Record the appearance of the acid in NaCl the data table. 5) Add about 10-20 drops of HCl to the Observations CO2 after the sodium carbonate. Record observations reaction H2O during the reaction on your data table. 6) When the reaction stopped, record your observations of each product formed. Disposal Pour solution down the sink the PLENTY of water. Rise and Instructions dry watch glass Sugar + Heat Part 2 C H O 12C + 11H O Part 2 – Sugar subjected to heat 12 22 11 2 1. Fold the sides of the aluminum foil to Observations C12H22O11 make a small tray. before 2. Put 1 small spoonful of Sugar onto your reaction foil tray. 3. Record the appearance of the sugar in Observations the data table. during 4. Place a candle on top of a piece of reaction: Use paper. tongs to hold 5. CAUTION: tie back long hair and loose foil clothing. Carefully light the candle. 6. Use tongs to hold the aluminum tray. Heat the sugar slowly by moving the Observations C tray gently back and forth over the after the flame. Record observations during the reaction H2O reaction onto your data table 7. When the reaction stopped completely, Disposal When cool throw foil and burned sugar in the garbage can record your observations of each Instructions product formed. Part 3 – Copper Sulfate plus Aluminum Copper Sulfate + Aluminum Part 3 1. Observe the small flask of Copper 3CuSO4 + Al => Al(SO4)3 + 3Cu Sulfate and a piece of Aluminum Observations before CuSO4 foil. reaction 2. Record the appearance of the Al copper sulfate and aluminum foil in the data table. Observations during 3. Place the foil into the flask of reaction copper sulfate solution and swirl (gently) for several minutes. Observations after Al(SO4)3 Record observations and the reaction. temperature during the reaction Use a craft stick to onto your data table see precipitate Cu 4. When the reaction stopped completely, record your Disposal Place test tube onto the rack on big lab table. Teacher will observations of the products Instructions dispose. formed. 3. Evidence of Chemical Reactions p96-97 To find out whether a new substance has formed during a chemical reaction, scientists use tests to determine the properties of those substances. They focus on properties that are known to be different for certain reactants and products. Some commonly tested properties are density, melting point, boiling point, solubility, flammability and odor. • These properties do not change with an object’s shape and size. • They only change if one substance changes into a new substance. 3. Evidence of Chemical Reactions p96-97 Boiling/Melting Change in Odor point density Change in “Characteristic" flammability Properties Color Change solubility Evidence of a Chemical Reaction Change Exothermic Formation of a NEW in Energy substance Endothermic Precipitate can Form Claim, Evidence & Reasoning: Chemical Reactions Provided below are pictures of three different scenarios in which two different chemicals are mixed together. For each scenario, make a claim about whether or not a chemical reaction is occurring. Provide evidence and reasoning to support your claim. If a reaction cannot be determined based on the provided picture, explain why not and how you could determine if a reaction has occurred. Use specific examples in your explanation. 1 Claim, Evidence & Reasoning: Chemical Reactions Provided below are pictures of three different scenarios in which two different chemicals are mixed together. For each scenario, make a claim about whether or not a chemical reaction is occurring.