Compounds_ Mixtures and Solutions

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Compounds_ Mixtures and Solutions Powered By Docstoc
					Get  out your notebook and
 turn to the warm up page
Write down any
 observations you can
 make about the two
 different substances in the
 jars on my desk
After    the
    demonstration, write
    down any new
    observations including
    what happened to
    each substance
Mixtures and
Compounds Vs Elements
        Compounds                 Elements

Pure  substances made     Pure substance that
up of two or more         can not be broken down
                          into simpler substances
The elements are
chemically combined        A single particle of an
                          element is called an
A single particle of a
compound is called a
Molecules are made up
of atoms of elements
Compounds Vs Elements
     Common Compounds       Common
Table salt              gold
-sodium and chlorine    Silver
Water                  Aluminum
-hydrogen and oxygen    Carbon
Vinegar                Oxygen
-hydrogen, carbon       hydrogen
and oxygen
Baking soda
-sodium, hydrogen,
carbon and oxygen
Properties of compounds
   Every compound has a unique set of
       These properties are similar to those of
       Ex: melting or boiling points, density, color,
   A compound’s properties are sometimes
    very different from the properties of its’
    individual elements
       Ex:
             sodium (an alkali metal) is a highly reactive solid
            Chlorine is a poisonous gas
            When they combine, they form table salt which is
             safe to eat
Break it down
   Some compounds can be broken down into their
    individual elements
       Ex: water can be broken down into hydrogen and
        oxygen by using extremely high amounts of energy
   Other compounds are broken down into simpler
    compounds which can then be split into their
       Ex: carbonic acid creates the bubbles in your soda
            Carbonic acid breaks down into carbon dioxide and water
             once the soda is opened
            The carbon dioxide and water then break down into carbon,
             oxygen and hydrogen
   Breaking down compounds can only be done
    through chemical changes and typically require
    the addition of heat or energy
Mix it up
   A mixture is a combination of two or more
    substances that are not chemically
       All of the substances keep their individual
       Ex: a salad – you mix all of the vegetables
        together in a bowl, but you still have individual
        carrots, lettuce, tomatoes, etc…
Where’d it go?
   You won’t always be able to see the
    substances that make up a mixture
       Ex: salt or sugar water
            salt and sugar both dissolve in water
            They retain (keep) their individual properties as does
             the water
            You can separate the salt or sugar by physical means
               Add heat to evaporate the water and you are left with
                the salt or sugar
Separation Anxiety
   How do separate the substances in a
       Through chemical changes
   How do you separate the substances in a
       Usually can be done through physical changes
            Ex
               magnetism to separate out metals
               Evaporation
               Distillation (using boiling points)
 Go back to your journal
 Explain which substance created
  a compound and which created a
  mixture when vinegar was added
   How do you know?
Warm up 10/5 –write the questions!!
Describe the difference
 between elements and
What is one particle of an
 element called?
What is one particle of a
 compound called?
What is the only way to break
 apart a compound?
Bond, Chemical Bond
 A chemical bond occurs when two or more
  atoms join to make a new substance
 To understand chemical bonding, you
  need to recall valence electrons
       We have discussed:
            You can determine the # of electrons in an atom
             based on its atomic number
            electrons in the outermost orbital (electron shell) are
             called valence electrons
       Valence electrons are typically the only
        electrons to be involved in bonding
            You can determine the number of valence electrons
             based on the group number of the atom
To bond or not to bond
   Not all atoms create chemical bonds
       The noble gases of group 18 already have a
        full outer orbital with 8 electrons so they are
       Therefore, they rarely bond with other atoms
   Atoms bond by gaining, losing or sharing
       Remember:
            group 1 will usually bond with group 17 – why?
               Group one wants to give away its one valence electron
                while group 17 wants to gain one more electron
            group 2 will usually bond with 16
   A chemical reaction is when one or more
    substances change to make one or more new
       Ex: baking a cake, burning wood
   Signs of a chemical reaction taking place:
       Gas formation (bubbles)
       Solid forming (called a precipitate)
       Heat or light given off
       Color change
   What does it mean if a chemical reaction has
       The bonds between atoms have been broken, the atoms
        rearranged and new bonds have been created
Reading in Chemistry
   Chemical formulas are shorthand ways to
    represent substances
       They use the chemical symbols from the
        periodic table and numbers to represent the
        elements and compounds
       Ex 1: H2O is the chemical formula for water
            The small 2 is called a subscript
               It shows that there are two atoms of hydrogen
            Because there is no subscript next to the O, there is
             only one atom of oxygen
       Ex 2: C6H12O6 = Glucose
            Glucose has 6 atoms of carbon, 12 atoms of
             hydrogen and 6 atoms of oxygen
Practicereading and
writing chemical
formulas as a class
Warm up 10/6 – write these questions on the
next page of your notebook not in your warm
up section and leave 1-2 lines between each
 What does the law of conservation of mass tell
  you about a chemical reaction?
 What is the mass of the experiment in the bag
  before you mix everything together?
 How do you know a chemical reaction took
  place in the bag?
 What is the mass of the experiment in the bag
  after you mix everything together?
 How does this lab demonstrate the law of
  conservation of mass?
Doing the Math
   Chemical equations use chemical formulas
    and chemical symbols to describe
    chemical reactions
       The reason for using chemical equations:
            They are shorter than writing out the reaction
            Anyone who can read chemical symbols can
             understand chemical equations
   Equations refer to the entire chemical
    reaction while formulas refer to a specific
    chemical compound or element
2 parts to an equation
   There are two sides to a chemical
    equation, separated by an arrow
       The left of the arrow contains the reactants
            These are the substances that you begin a reaction
       The right of the arrow contains the products
            These are the substances that you end up with after
             a reaction
       Ex: C + O2  CO2
            C O2 and are the reactants
            CO2 is the product
Balancing act
   Atoms are never lost nor gained in a
    reaction, they are just rearranged
       The number of atoms in the products have to
        equal the number of atoms in the reactant
       A french chemist found that the total mass of
        the reactants was always the same as the
        total mass of the products
            This is called the Law of Conservation of Mass
 Experiment in a bag mini - lab
 1. place the zip loc bag on the balance
 2. pour the baking soda into the bag
 3. CAREFULLY PLACE the cup of vinegar in
  the bag – DO NOT SPILL THE VINEGAR!!!!
 4. seal the bag tightly
 5. find the mass of the bag and its contents
 6. without opening the bag, tip over the
  vinegar cup
 7. find the mass of the bag and its contents
 8. answer the questions from your warm up
Warm up 10/7 – be sure to write the questions!!!!
1.   What is a chemical formula?
2.   What is the little number next to an
     element symbol in a formula
3.   What does the little number mean?
4.   What is a chemical equation?
5.   What is the difference between the
6.   What does the law of conservation
     of mass tell us?
    Balancing Act
   Balancing equations lets you show that there has not
    been any mass gained or lost
       When you balance an equation, you show that there are
        the same number of all atoms before and after a
   Some compounds will have a number in front
    of the chemical formula
       Ex: 2H2O
       The 2 in front is called a coefficient
            It symbolizes that there are two molecules of water
               This means that there are a total of 4 hydrogen atoms and 2
                oxygen atoms

   When you balance an equation, you can
    change the coefficient of any of the reactants
    or products
Balance this equation
H2 + O2 H2O
Step 1: Count the number of atoms of each
   H2 + O2 H2O
  2H 2O 2H 1O
Step 2: start by balancing the oxygen atoms –
  place a coefficient of 2 in front of the water
  H2 + O2 2H2O
  2H 2O        4H 2O
Step 3: balance the hydrogen atoms – place a
  coefficient of 2 in front of the hydrogen formula
  2H2 + O2 2H2O
  4H     2O 4H 2O
 Which of these
  substances are mixtures?
  Why do you think so?

Sand       Salt Water   Steel   Air
The answer is the Solution
   We’ve talked about mixtures before
       A mixture is created when two or more
        substances are physically combined
       A solution is a type of mixture that appears to
        be one single substance
            It is particles of two or more substances that are
             distributed evenly among each other
            Solutions are created because of the process of
            Ex: salt water, sugar water
Which is dissolved into which?
   The solute is the substance that is
       Salt is the solute in salt water
   The solvent is the substance that the
    solute is dissolved in
       Water is the solvent in salt water
   The ability to dissolve is called solubility
       If a substance can not dissolve in a solvent, it
        is said to be (called) insoluble
Is it always a liquid?
   Examples of solutions:
       Tap water
       Soft drinks
       Gasoline
   Solutions aren’t always liquids
       Air, a gas, is a solution
            Multiple gases are evenly spread out among each
       Alloys, metals melted within each other, are
        solids and solutions
It takes Concentration
   Concentration is the measure of the
    amount of solute dissolved in a solvent
       Solutions can either be dilute or concentrated
            If there is less solute in a solution, it is dilute

            If there is more solute in a solution, it is concentrated
Journal #13
What  is the difference
 between a general mixture
 and a solution?
What is concentration (in
 terms of solutions)?
What does it mean if a
 solution is diluted?
The Suspension is killing me!
   A suspension is a mixture in which
    particles that are mixed with a liquid are
    large enough that they are able to settle
       IE: Snowglobes

       If you leave a snow globe sitting on a desk,
        the snow particles will fall to the bottom
             They are too large, and too heavy, to stay
            suspended in the liquid
Properties of a suspension
   Suspensions scatter or block light
       If you were to shine a flashlight through a
        suspension, you would not get a solid beam
        out the other side
   Suspensions can be separated by passing
    the mixture through a filter
       The filter will catch the large particles and
        allow the water to drain out
What do you get when you cross a
solution and a suspension?
   A colloid!
       A mixture where the particles are dispersed
        throughout, but are not heavy enough to settle
            Ex: the dust you see in a ray of light
            Ex: fruit particles in a jello mold

   Properties:
     Particles can scatter light
     Particles can not be separated
    by filtration because they are too
    small and light