1. Chapter 2 Most Missed Topics

2. Physical Properties/Changes Color (if I paint my white car red), Density, Hardness, Texture Phase (PHASE means matter is either a gas, liquid, or solid; if you change the phase, it is only a physical change) Changing shape Dissolving (dissolving salt and water—let your water evaporate and you will have your salt again) RESTORING your original conditions WILL allow you to get your original substance  PHYSICAL change

3. Physical Properties/Changes How do you change from one phase to another? ◦Solid  Liquid MELTING ◦Liquid  Gas EVAPORATION (BOILING water causes it to change from liquid to gas and evaporate) ◦Gas  Liquid CONDENSATION ◦Liquid  Solid FREEZING ◦In order to have a phase change, this requires that a substance would either BOIL or MELT at some temperature, i.e. BOILING POINT and MELTING POINT are physical properties.

4. Chemical Properties/Changes Flammability BURNING Reactivity – If something can REACT with something else to form something NEW Signs of chemical changes—color (if it is RUSTING, fading from the sun, caused by reactions—you didn’t pull out your paint brush and change it yourself!), noticeable odor, formation of bubbles (INDICATES A GAS IS BEING MADE), formation of a precipitate ◦If a NEW substance is made, it is a chemical change. ◦If you restore the original conditions, and CANNOT get your original substance, then it is a CHEMICAL change

5. Which of the following is NOT a chemical change? (question 3) Release of gas Evaporation of water Change of color Production of gas ◦You should be able to immediately eliminate “release of gas” and “production of gas” because those are DEFINITE indicators of a chemical change ◦Change of color could be either physical or chemical depending on how the color was changed… ◦BUT evaporation of water (PHASE CHANGE, LIQUID  GAS) is DEFINITELY a physical change, and therefore should be chosen as the correct answer.

6. Which is an example of a chemical change? (question 26) Ice melting Pounding gold into a coin Paint fading A puddle of water evaporating ◦Lets go choice by choice… ◦Ice melting – it is a PHASE change, solid  liquid so DEFINITELY physical ◦Pounding gold into a coin – you are changing the SHAPE, it is still gold, so DEFINITELY physical ◦Paint fading – maybe you’re not sure at first? ◦A puddle of water evaporating – PHASE change, liquid  gas, DEFINITELY physical ◦Therefore, it has to be paint fading, even if you didn’t originally know that this indicated a change in chemical properties

7. Questions 3, 9, 10, 12, 15, 20, 26, and 32 were some of the MOST missed questions… and it was only because there was not an understanding of the difference between physical and chemical properties/changes… we did numerous worksheets and packets that I then gave you answers to in order to study from them.

8. Pure Substance Element, Compound, Molecule They are CHEMICALLY combined—water is a compound, the hydrogen and oxygen are chemically bonded to one another. Mixtures are NOT pure substances. I used the example (NUMEROUS times), if I take paper clips and marbles and put them into one jar, this is a mixture. Is a jar of marbles and paper clips pure? NO.

9. Compounds Two or more elements chemically combine (RECALL: an element is made of only one type of atom, therefore if the question asked what is made of at least two different types of atoms, that is like saying what is made of at least two different elements) Substances LOSE their properties when they form compounds They CANNOT be physically separated Water—made from oxygen GAS and hydrogen GAS, but it is a LIQUID. I cannot physically separate the oxygen and hydrogen atoms by picking them out with my hands, using a filter, etc. Table Salt—made from sodium and chloride atoms. In standard conditions, sodium is a soft, silvery metal and chlorine is a yellow-green gas. I cannot take a grain of salt and separate it into sodium and chlorine atoms by physical means.

10. Mixtures NOT chemically combined Substances KEEP their own properties They CAN be physically separated Pepperoni pizza—cheese and pepperoni off the pizza are the same as when they are on the pizza, I can pull the pepperoni off to separate my mixture.

11. Miscible vs. Immiscible Refers to mixtures of liquids Miscible mixtures are liquids than can be mixed – like gasoline. Immiscible mixtures are liquids that cannot be mixed – like oil and water.

12. Physical Science We are studying topics in both CHEMISTRY and PHYSICS during this course Chemistry—the study of matter and how it changes Physics—deals mostly with energy and forces (this was a question on your chapter 1 test) Therefore, we are currently studying topics in chemistry