Middle School SCIENCE -- Mrs. White

-      Mixture – a combination of 2 or more pure substances that are NOT chemically combined

·        Do not react to form a compound

·        NO chem. ∆ happens; no bond has formed

·        Each substance has its own chem. make-up as it had before mixture formed

·        Each substance keeps its identity, & their individual properties

·        Separated by physical means only

-      Common ways to separate mixtures

1)   Filtration – trap solids by pouring thru filter

2) Evaporation – heat mixture to evaporate out liquid

3) Distillation – mixtures separated based boiling pts

4) Magnet – separate out thru magnetic property

5) Centrifugation – separate based on densities

-      Mixtures do not have specific mass ratio       ie: granite, soil

-      Solution – 2 or more substances that are evenly distributed; a well-mixed mixture

·        Appear to be a single substance; particles too small to see

·        Have same appearance & properties throughout the mixture

·        Dissolving – process in which particles of a substance spread out evenly throughout a mixture

ie: salt or sugar water

·        All solutions have at least 2 parts:

1)   Solute – the substance that is dissolved; must be soluble         ie: salt or sugar

2) Solvent – the substance in which a the solutedissolves        ie: H₂O

§ Present in lg’r amt.

§ Dissolves other substance

§ H₂O often the solvent – “universal solvent”

·        Insoluble – unable to dissolve: mixture is NOT a solution

·        Solutions may be gas, liquid, or solid (alloy)

(See Table 2, p.67)

·        Particles in solution:

§ too small to settle out

§ cannot be removed w/out filtering

§ don’t scatter light (light does not appear to shine thru)

-      Compounds – a pure substance composed of 2 or more elements that are chemically combined

·        Elements are rarely found alone; combined w/ other elements

·        Elements undergo chem. ∆ (react chemically) w/ each other to form new pure substance

·        Elements are bonded tog. in predictable #’s:

§ Join in specific ratio according to their mass, which never ∆’s

ie: H₂O     H : O = 1 : 8    

mass of 2 H’s = 2 : mass of 1 O = 16   

2 : 16   Þ   1 : 8

§ Bonds hold elements tog.

-      Each compound has its own unique physical & chemical properties

·        Properties determined by atomic structure

·        Properties will differ from those of the properties of elements that form them

·        ie: Salt (NaCl)

   Na      +      Cl      Þ      NaCl

  unstable solid + poisonous gas Þ stable solid

-      Compounds can break down into simpler compounds or elements thru chem. ∆

ie:  (Carbonic acid) H₂CO₃   Þ CO₂ &  H₂O

CO₂   Þ  C & O₂      

1)   Є can be added to break down compound (endothermic) :

§ Apply heat

§ Electric current

2) Є can be released to break down compound (exothermic) :

§ Any burning reaction

§ Breakdown of foods       ie: C₆H₁₂O₆ Þ CO₂ & H₂O

-      Compounds in industry:

·        Elements not usually found in pure form in nature: must be broken down further                

·        Most must be broken down to use as raw materials

ie: aluminum, ammonia

-      Important compounds in nature:

·        Proteins

§ Found in all living things; needed to make new proteins

§ Proteins in food are broken down into simpler compounds: a.a. (amino acids), for which N is needed to make new proteins

§ Animals’ source of N comes from plants (directly or indirectly)

§ Plants get N through N-compounds found in soil

·        CO₂

§ Plays important role in life:

§ Necessary for photosynthesis in plants, to make compounds called carbohydrates

§ Carbo.’s broken down for Є by plants & animals