Read B-39 Problem: How are reactants changed by a chemical reaction? How are the products different? Hypothesis/Initial Thoughts:
Background: Chemical Reactions occur during every day activities like cooking, cleaning and bleaching laundry can’t be observed at a molecular level generally use indirect indicators to infer that a chemical reaction has taken place Color change Formation of a new substance with properties different from the original reactant release of a gas heat given off or absorbed light or sound given off
Iron powder and sulfur are mixed. A heated metal rod initiates an exothermic reaction
Examples of chemical reactions: –Burning fuel to heat homes –Combustion of gasoline to power cars –The human body using a reaction between food and oxygen to produce carbon dioxide and water, releasing energy –Baking bread or cookies Background cont.:
H C C HO H H Background: Create this molecule Vinyl alcohol Draw it in your notebook Link your vinyl alcohols together
You can use all of these single molecules to build a long chain. Use extra bonds to link your molecule to the other molecules. You modeled a chemical reaction between vinyl alcohol molecules. One function of a model is to make simple representations of complex systems Molecular models allow us to visualize what is happening at the molecular level
You will be using Polyvinyl Alcohol today. The long chain is called a polyvinyl alcohol, because “poly-” means many. In any reaction like this, the starting subunit part is called a monomer, which means “one part”, and the resulting chain of many parts is called a polymer, which means “many parts” We made Polyvinyl Alcohol
One Vinyl Alcohol Molecule = monomer Long Chain Polyvinyl Alcohol = polymer –1,000-10,000 monomers form a polymer. “Poly” means many “Mono” means one Background cont.:
Draw it in your notebook More monomer links H C C HO H H H C C HO H H Polyvinyl Alcohol More monomer links
Background cont.: Reactants + Reactant Product + Product Sodium and Water Demo: 2Na + 2H 2 O 2NaOH + H 2 Reactant: a substance that undergoes change in a chemical reaction Product: a substance formed as a result of a chemical reaction
Examples of Plastics Polypropylene (Blue) Polyvinyl Chloride (Green) High Density Polyethylene (Red) Polystyrene (Yellow) What do you notice about the names of these materials?
Read Steps 1-8 on B40 to B41 LEAVE ROOM (AT LEAST 10 LINES) FOR YOUR DATA TABLE!!
What will be our evidence of a chemical reaction? What are some of the rows that we will need to label on our data table??
What will be our evidence of a chemical reaction? Color How does it pour? Can it be stirred? Stickiness Bounciness Stretchiness Other Observations
In this activity you will start with the polymer known as polyvinyl alcohol (PVA) and see how its properties change when it is mixed and reacts chemically with another compound, to change its molecular composition. Stir the mixture constantly and slowly until a gel forms Clean and dry the materials quickly!!!! Everyone wash your hands after you have put away your goggles and gloves
It is the number of cross-links that determines the properties of a polymer Which do you think is a harder substance, a polymer with more cross-links or a polymer with fewer cross- links? The sodium borate created the cross-links with the polyvinyl alcohol What do you think would happen to the final polymer if you continued to add sodium borate? Cross-linked plastics are more rigid Follow-up
What are the physical properties of the reactants? Describe the physical properties of the product. What evidence show a new substance was formed? –change in physical properties indicates an new substance has been formed