Observations Direct Observations Those observations we make ourselves Indirect Observations Those observations that we figure out from direct observations
Observing Milk Consumption The cafeteria is considering getting rid of milk at lunch. Before they do, they need to know how many students drink milk each day. List as many ways as you can to find out how many students drink milk each day.
Comparing Observations Observation Time Cost Accuracy Direct Lots Expensive High Indirect Little Cheap Low
Chemical Reactions Lab Activity #1: Observe the teacher ripping and burning paper and complete the data table. Chemical Reaction Chemical bonds are formed or broken Physical changes are not chemical reactions
Evidence of Chemical Reactions Lab Activity #2: Observe the teacher mixing different materials and complete the data table. Evidence of chemical reactions 1. Energy is released 2. Precipitate Forms 3. Color Change 4. Bubbles 5. Change is difficult to reverse
Variables Independent (manipulated) Variable The variable that YOU assign Dependent Variable The variable that responds to what you do Does Mountain Dew wake you up faster than coffee? _how fast you wake up depends on type of drink_ 1. Does ice melt faster in the sun or shade 2. Will 5 mg or 10 mg of medicine make your headache go away faster 3. Are diesel or gas engines more fuel efficient 4. Will salt water boil faster than fresh water
Chemical Equations Equation Description of the chemical reaction Reactants Ingredients or substance before reaction Reactants go on left side of equation Products Substance after the reaction Products go on right side of equation Equations are balanced so you have the same number of atoms on both sides of the equation
Two Important Chemical Reactions Sunlight 6 CO 2 + 6 H 2 O C 6 H 12 O 6 + 6O 2 Chlorophyll C 6 H 12 O 6 + 6O 2 6 CO 2 + 6 H 2 O
Reaction Rates Lab Activity #3: Carry out the following tests 1. Drop a half tablet of alka-seltzer into water and a half tablet into vinegar 2. Drop a half tablet of alka-seltzer into hot water and a half tablet into cold water 3. Drop a half tablet of alka-seltzer into water and stir it and a half tablet into water that is not stirred 4. Drop a half tablet of alka-seltzer into water and a crushed half tablet into water
Rates of Chemical Reactions Chemical Reaction occur when atoms collide Reaction rates change from increasing or decreasing collisions Ways of changing reaction rate: 1. Nature of reactants 2. Concentration 3. Pressure 5. Catalysts 6. Agitation 7. Surface Area 4. Temperature
Energy and Chemical Reactions Lab Activity #4: 1. Place a 25 ml of vinegar and a thermometer in a small glass beaker 2. Record the temperature 3. Add 10 g of baking soda and observe any changes in temperature 4. Place a 25 ml of hydrogen peroxide and a thermometer in a small glass beaker 5. Record the temperature 6. Add 10 g of yeast and observe any changes in temperature
Energy & Chemical Reactions Endothermic Requires energy Energy Exothermic Releases energy Reactants have less energy than products Breaking bonds requires energy Activation energy is part of the reaction Products have less energy than reactants Few reactions Majority of reactions
Types of Chemical Reactions Synthesis Reactions Combination Exothermic Simple to Complex 2H 2 + O 2 2H 2 O Replacement Reactions Elements trade places Endo or Exo Thermic i.e. Cl + NaBr Br + NaCl Decomposition Reactions Separation Endothermic Complex to Simple 2H 2 O 2H 2 + O 2 Combustion Reactions Synthesis Reaction Reactant: O 2 and some compound Product: H 2 O and CO 2 i.e. Burning wood
Acids, Bases, and ph Acid Anything that produces H 3 O + (hydronium ions) in water Base Anything that produces OH - (hydroxide ions) in water ph Logarithmic measure of H+ ions <7 = Acid 7 = Neutral >7 = Base
Measuring Acids and Bases Acids Neutral Bases 0 7 14 10-7 Mole H + ions/liter 1 Mole H + ions/liter 10-15 Mole H + ions/liter What s a Mole 6.02 x 10 23
ph Within organisms, ph must be carefully maintained or death will result. In order to prevent ph imbalances, buffers are produced to moderate changes to acids and bases in the body.
The ph of Beans Lab Activity #5: Place 10 beans in a 100-ml beaker. Each bean will represent a H + ion and the beaker will represent a solution with a ph of 7 (neutral). Now make a beaker with 1 bean and a beaker with 100 beans. The 1 bean solution is a ph of 8 (basic) while the 100 beans are a ph of 6 (acidic). Use the beans to help you answer the questions in your lab packet.
Measuring ph Lab Activity #6: Acids and Bases Special paper called litmus paper can be used to estimate the ph of different substances. Predict the ph (acid or base) of the following substances. Then test the substances using the litmus paper provided. Tap Water Soda Water Starch Solution Vinegar Milk Apple Juice Cranberry Juice Coffee Tea Lab Activity #7: Measuring ph Better results can be obtained using a ph meter. Predict the ph (1-14) of the following substances. Then test the substances using the ph meter provided. Tap Water Soda Water Starch Solution Vinegar Milk Apple Juice Cranberry Juice Coffee Tea