Ch. 2.2 and 2.3 Mixtures, Elements, Compounds

Symbols Chemists use chemical symbols to represent elements Chemical Symbol: 1 st 1-2 letters of the name of the element –1 st letter is Capitalized –2 nd letter is lower case  Examples: Co = Cobalt; O = Oxygen; Be = Berylium Exception: Some use the letters from the Latin name  Examples: Fe = Iron (Ferrum) K = Potassium (Kalium) Cu = Copper (Cuprium)

Formulas Chemists use chemical formulas to represent compounds –Compounds: 2 or more elements  Examples: NaCl = Sodium Chloride H 2 O = Water

Na + Cl 2  NaCl Sodium + Chlorine  Table salt

H 2 + O 2  H 2 O

Distinguishing Substance and Mixtures Matter Substance: Definite Composition (Homogeneous) Element Ex: Sodium Na Compound Ex: Sodium Chloride Mixture of Substance: Variable Composition Homogeneous Mixture: Uniform; also called a Solution Ex: Salt in Water Heterogeneous Mixture: Non-uniform; Distinct phases Ex: Milk Physical Separation? No Yes Chemical Separation? YesNo

Heterogeneous V. Homogeneous

Paper chromatography Separating a mixture

Law of Conservation of Mass During any chemical reaction or physical change, the mass of the products is always equal to the mass of the reactants Bottom line: you cannot create or destroy matter. Matter is conserved. What about burning wood?????

Chromatography Lab Problem: A crime has been committed!! Can you match the pen used to write the note? Hypothesis: Materials: Pens, filter paper, tape, cup of water Procedure: Write your own procedure! Data: Draw a diagram of your filter paper. Label ink dots and show what happened, use colored pencils. Conclusion: Which pen was used in the crime? How do you know? What type of mixture was the ink?