Physical and Chemical Changes Friday, Sept 29

Physical Changes Definition: the chemical nature of the material remains unchanged. Evidence/ examples Ripping, molding, or reshaping the material Molding clay Phase changes Solid -> Liquid -> Gas Dissolution (dissolving) or recrystalization For example, formation of rock candy

Chemical Changes Definition: The chemical identity of a substance is altered Evidence/Examples A change in the odor or color of a material Formation of large amounts of energy Heat, light or electrical Formation of a new form of matter with a different boiling point or melting point Formation of gas bubbles from a solid or liquid A white or colored solid appearing around the shower head (called precipitation)

Lab Stations – General Instructions Record all observations and thoughts in your lab notebook Visit each station. Identify the elements that make up the compounds used. Describe any and all physical or chemical changes that occur at the lab station. Record observations Suggest an investigation you might like to attempt to further your understanding of the situation presented at each station.

Lab Station #1 Rock Salt – 1 scoop Describe what happens. Crush rock salt crystals (NaCl) using the mortar & pestle. Add the crushed rock salt to the beaker of H2O. Describe what happens. Where do the crystals go once placed in the H2O? Is it a physical or chemical change? How do you know? How does the stirring device work? Propose a further investigation.

Lab Station #2 Place a scoop of calcium chloride into a baggie and add 10mL of water. Make observations. Repeat using the sodium bicarbonate. Add a dropper of phenol red to each and observe. Place both baggies into a Ziploc bag and seal. After sealing mix the contents and observe. Attempt to assign responsibility for each observation to a chemical involved in this station.

Lab Station #3 What are the bubbles made up of in the beaker of water? Describe what you believe is happening to the molecules in the beaker. Use an illustration to provide another description of what is happening to the molecules.

Lab Station #4 Add a nail to the copper sulfate solution and observe. Remove the nail after a length of time and record observations. Hypothesize as to the cause and nature of the change.

Lab Station #5 Place 5 kernels of popcorn into a 250mL and cover with clear plastic wrap. Poke a hole in the middle of the plastic wrap. Heat on a hot plate. Respond to the questions on page 71 of your text.

Lab Station #6 Obtain 3 test tubes that fit into the test tube rack provide. Add a dropper of the KOH to a test tube and a dropper of HCl to a second test tube. Add a dropper of both KOH and HCl to the third test tube. Add one squirt of phenolphthalein to each test tube and record observations.