TAKS Review: Chemistry Focus on basic properties of matter!

Physical Properties Describe the physical nature of matter, not its chemical behavior. Examples: Melting point, boiling point, freezing points, color, viscosity, density . . . Melting and boiling points along with density are ways of identifying unknown substances

Chemical Properties Properties that describe the chemical behavior of matter. Formation of cations (+) or anions (-). Combines with oxygen or burns in air. Anything related to reactivity.

Physical and Chemical Changes Rotting, burning, cutting in half, vaporizing, rusting, explodes ….. So, which of the above are physical changes and which are chemical? Ask, which of the above changes the essence of the matter? Exploding is chemical, why? It’s a reaction! Cutting in half? Physical; it’s still the same stuff.

Evidences of a chemical change! Precipitates = solids formed when 2 clear liquids mix. Gas given off Color change (be careful, can be physical only, but a color change often accompanies a chemical one). Heat (exothermic or endothermic). Light.

Exo or Endo Heat = - 510 kilojoules Heat = +510 kilojoules If Heat is +, it’s endothermic (Temp. drops) If Heat is -, it’s exothermic(Temp. increases

Density vs. Weight What’s the difference between density and weight? Which changes if you suddenly land on the moon? Weight! Density is a ratio of your mass to volume which shouldn’t change if you made it safely. If a block of wood is cut in half, how does that change the density? It doesn’t!!

Viscosity Thickness of a liquid based on bonding. Syrup is more viscous than water because of the cohesive bonding of the molecules. How would you measure the viscosity of a liquid? Drop a marble in it and time it. I know, it sounds stupid, but we’re trying to pass the test. The longer it takes for the marble to reach the bottom in equal amts., the more viscous.

Review Your Periodic Table Know the difference between a Group and a Period. Groups, vertical. Group I has Li and Na which have similar properties because they have 1 valence electron and form +1 ions to achieve a stable octet. Periods, horizontal. Have same outer energy levels. 4th Pd = 4th outer level.

Parts of the Table Transition metals/Alkali metals Halogens Noble gases; what’s special about them? Calcium will form what kind of ion with what magnitude of charge? 2+ Chlorine ? 1- Formula?? CaCl2

3 states of Matter Solids Liquids Gases Describe the molecular motion for each state. What is the relationship between the strength of the bonding and matter’s physical state? Stronger bonds tend to form solids.

Types of Bonds Ionic = metal and non-metal Na+ + Cl-  NaCl Covalent = sharing e’s; non-metals. H – Cl share 1 pr. of e’s. Ionic – crystals Covalent – some solids, liquids and gases. Gases tend to be non-polar covalent.

Balancing Equations First, write the correct “formula” for a compound if it’s not given. Ca + O  CaO Ca+2 + O-2 = CaO so the charges =0 Mg+2 + Cl- = MgCl2 magnesium chloride Mg+2 + PO4 -3  Mg3(PO4)2 magnesium phosphate

So, put it together KClO3  KCl + O2 2,2,3 H2 + O2  H2O 2,1,2

Kinetic Energy and atoms The More KE atoms have, the more they move. Bonding holds them together Gases have little bonding, so adding more heat (Kinetic Energy) causes them to move a lot. Gas molecules moving around eventually cause collisions which create gas “pressure” inside a container. Increase the temperature (KE) and the gas pressure increases. Why?

Law of Conservation of Mass Mass of Reactants = Mass of Products 2H2 + O2  2 H2O 11 g. ? 23 g. 11 + ? = 23 then ? = 12 grams!

3 forms of Matter Elements: the purest form of matter. * Check the periodic table. Compounds: combinations of elements in a specific ratio ( water is H20, not H202). Mixtures: compounds and elements tossed together in any proportion.

Mixtures: types of. Homogenous: the mixture looks the same throughout. - kool aid, salt water, milk . . Heterogeneous: mixture maintains separate parts. - rocks and water, dirt.

Solutions: a type of mixture Made of a solute (what gets dissolved) and a solvent (what does the dissolving). Homogeneous and Heterogeneous solutions. See last slide. Water is always the solvent, salt is a solute. Unsaturated, saturated and super-saturated solutions.

Acids & Bases Solutions can be acidic or basic. Acid solutions taste sour, Basic solutions taste bitter. Lemon vs. Soap. pH is a scale used to identify weak solutions as either acidic or basic. 7(neutral) 0 Acidic Basic 14

Types of Acids/Bases Acids: hydrochloric acid (HCl) is a Strong acid Organic acids like citric or vinegar are weak acids. Strong base solutions are often called alkaline or caustic. If a solution has a pH of 10, it’s basic and would require vinegar, maybe, added to it to bring the pH down. That’s why they put citric acid in your shampoo which is normally basic because it’s a soap down to 5.5 which is the pH of your hair.

Water Acids are made of Hydronium ions (H3O+) in water. Bases are made of Hydroxide ions (OH-) in water. Water is neutral, a pH of 7, because the number or concentration of H3O+s = OH-s. H3O+ + OH-  2 H2O (neutral) acid base