Transcript Compounds Galore! - Johnston County Schools

Compounds, Mixtures,
Solutions and Reactions
Classifying Matter
Matter
Pure Substances
Mixtures
Homogeneous
Elements
Compounds
milk, tea
Fe, O
H2O, CO2
Heterogeneous
Rocky Road ice
cream, muddy
water
What is a Pure Substance?
• A pure substance is a classification of
matter that includes both elements and
compounds
• Pure substances cannot be separated by
physical means such as distillation,
filtration, or chromatography
Elements
• We will study elements in depth later, but
be sure to know…
− An element is made of one kind of atom
− Found on the periodic table
What Is A Compound?
• A compound is a pure substance that is
created by 2 or more elements chemically
reacting and joining together
− Ex: NaCl, H2O, CO2, NH3, NaHCO3, and
C6H12O6
• Notice that elements combine in many
ways to make compounds
− Ex: H2O, H2O2, CO, and CO2
Why Do Compounds Form?
• Compounds form to allow elements to
become more stable
− Na is flammable when it comes in contact
with H2O, and Cl2 is a toxic gas
− NaCl is a very stable compound that is
neither flammable nor toxic (in normal
quantities)
• Compounds that are extremely unstable
will break down to form the more stable
elements
How Do Compounds Form?
• Compounds form by the interaction
between the nuclei and valence electrons
of 2 or more elements.
What Do Compounds Have To Do With
My Life?
• Compounds are the substances that make
up ALL living and non-living things
• Examples: Where would you be without:
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−
−
−
H2O—water
NaCl—table salt
C3H8O—rubbing alcohol
C55H98O6—an example of an
unsaturated fat
What Is A Mixture?
• A mixture is the physical combination of 2 or more
substances
• It is important to understand that a mixture is not
chemically combined
• Mixtures can be separated by physical means such
as filtration, distillation, and chromatography
• Mixtures can be divided into 2 groups
− Homogenous mixtures
− Heterogeneous mixtures
How Do Mixtures Form?
• Mixtures form by physically “junking” 2 or
more substances together
• Remember no chemical change is
occurring
• The formation of a mixture is not a result of
lowering energy
What Is a Homogenous Mixture?
• A homogeneous mixture is a mixture that is evenly
distributed
• Homogeneous mixtures are commonly called
solutions.
− Solution = Solute + Solvent
• Solute: “stuff” being dissolved
• Solvent: “stuff” doing the dissolving
• The solvent is present in greater quantity
• The solute is present in the lesser quantity
− Ex: Salt water: Salt=solute, Water=solvent
What Is a Heterogeneous Mixture?
• A heterogeneous mixture is a mixture
that is unevenly distributed.
• Examples:
− Iced tea: The ice is floating at the top
and therefore is not evenly distributed
throughout the tea
− Chex Mix: You may find a different
number of pretzels or Chex cereal in each
handful; therefore, the mixture is
unevenly distributed
How Are Mixtures Important To My
Life?
• We encounter mixtures everywhere in our
lives
• Where would you be without:
−
−
−
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−
−
Ice cream
Kool-aid
Shampoo
Soup
Milk
Orange juice
Pop Quiz Question #1
• Place an S beside each solution
and an M beside each mixture
S
_____ seawater
S
_____
steel
M
S
_____
salad
M
_____
air
Solutions
• Solutions can be solids, liquids, or
gases
• One substance dissolves in another
solvent --The substance that does the dissolving
*Water is the most common solvent.
solute
--The substance that gets dissolved
Rule #1: Usually there is more solvent
than solute
What Affects Solubility?
• Demo 1: Motion
−Rule #2: stirring helps to break up
particles and bring particles in contact
with the solvent
• Demo 2: Particle Size/Surface Area
−Rule #3: the smaller the particle, the
faster a solute will dissolve
• Demo 3: Pressure
−Rule #4: For gases, the higher the
pressure, the more gas that can be
dissolved in a liquid
• Demo 4: Temperature
−Rule #5: increase in the
temperature of the solution
increases the solubility of a
solute
−Rule #6: Adding a solute will
decrease the freezing point
and increase the boiling
point
−Rule #7: the more solute in a
solution, the less additional
solute that will dissolve; the
more solvent, the more
solute can be dissolved
• Saturated solution: contains the
maximum quantity of solute that can dissolve in a
certain quantity of solvent
− Supersaturated
Pop Quiz Question #2
• Which is the solute? Which is the solvent?
• A. salt in water
• B. 40% tin in 40% copper
• C. strawberries in cream
• D. carbon dioxide gas in water
Amounts of Solute
• A solution’s concentration depends on the amount of
solute dissolved in the solvent
− A solution with a high concentration has a large amount
of solute
− A solution with a low concentration of solute is called a
dilute solution
Solubility
• Solubility is the ability of a substance to dissolve in
another substance
• It is the amount of substance that will dissolve in a
certain amount of solvent at a given temperature
− If a solute is highly soluble, a solution will be very
concentrated
− If a solute has a low solubility, the solution will be dilute
Solutions/Solubility Video
• http://app.discoveryeducation.com/sear
ch?Ntt=solutions+and+solubility&N=18342
&N=4294949582&N=4294939055
• Do p. 545 question 1-4 and p.550
questions 1-4
How Can We Change Matter Into New
Substances?
• Chemical reaction (also known as a
chemical change) is a change in a
substance or substances that results in a
totally new substance
− Ex: 2H2(g) + O2(g)  2H2O(g)
Notice that the reactants (the substances
you start with) combine to form a new
substance (the product)
How Do I Know If A Chemical Reaction
Has Occurred?
• There are 5 indicators of a chemical reaction
1. Evolution of a gas
2. Evolution of light
3. Evolution of heat
4. Color change
5. Evolution of a precipitate
Precipitate: an insoluble substance that is
produced as result of a chemical reaction
Why Do Chemical Reactions Occur?
• Chemical reactions occur to produce a
more stable product than the existing
reactants
− Ex: 2Na(s) + Cl2(g)  2NaCl(s)
*The sodium is highly unstable and the
chlorine gas is somewhat unstable. The
resulting Sodium Chloride is VERY stable.
**It is important to understand that the
products have totally different properties
than the reactants
Where Does The Matter Go?
• It is important to understand that when
matter undergoes a chemical reaction (ie
a chemical change) it does not disappear
or appear
− The atoms are rearranged and form new
bonds, but no matter is lost nor gained
• This is called the Law of Conservation of
Matter
What Kind of Chemical Reactions Do I
Experience?
• The acidic milk and basic baking soda
that produce CO2 gas when a cake bakes
• Paper burning to produce ashes, CO2, and
H2O vapor
• Hydrogen peroxide decomposing to
produce water and oxygen gas
Exothermic Reactions
• A reaction in which energy is released
• Often produces an increase in temperature
• Reactants = Products + Energy
Exothermic Examples
• Glow sticks- work by a chemical reaction
that releases energy as light
• Fireflies- light up by a reaction that takes
place between oxygen and a chemical
called luciferin
Endothermic Reactions
• A reaction in which energy is absorbed
• Often produces a decrease in temperature
• Reactants + Energy = Products
Endothermic Examples
• Instant cold pack
• Photosynthesis
• Baking a cake- The cake batter will not
bake unless it absorbs energy