BR 2/13

1
BR 2/13

• Identify whether each substance or combination of
  substances is a pure element, a compound, or a
  mixture of elements or compounds. Write down the
  chemical formulas in addition to your response.
• O2
• O2 He
• CO2
• C2H6O and H2O
• O2, H2O, N2, and CO2

2
Illustrating elements, compounds, mixtures

• Identify which image represents each item in the
  BR.
• a. b. c.
• d. e.

3
Compounds vs. Mixtures

• In an illustration, how can you tell the
  difference between a compound and a mixture?
• What does each color represent?
• What would a mixture of elements look like?
• What would a mixture of compounds look like?

4
Compounds

• Made of elements in a specific ratio that is
  always the same H2O (water) is VERY different
  from H2O2 (hydrogen peroxide)
• Can only be separated by chemical changes, not
  physical changes
• Have their own physical chemical properties
  that can be different from what they're made
  of...
• EX. H2O is water, which is a liquid at room
  temperature although H and O are both gases at
  room temperature

5
Mixtures

• A mixture is a combination of two or more pure
  substances that are not chemically combined.
• Substances are held together by physical forces,
  not chemical ones
• No chemical change takes place when you make a
  mixture
• Each part of the mixture keeps the same
  properties it had before it was mixed
• Mixtures can be separated physically

6
Mixtures

• Homogeneous mixtures are when molecules are mixed
  up in an even distribution (so if you take two
  samples from separate parts of the mixture, they
  should be identical)
• EX sugar water, lemonade, Kool-Aid, soda, air
• DRAW what you think a homogeneous mixture would
  look like with legos

7
Mixtures

• Heterogeneous mixtures are when molecules are not
  mixed up in an even distribution
• EX snow globe, muddy water
• DRAW what you think a heterogeneous mixture would
  look like with legos

8
HW Elements, Compounds, Mixtures Assignment
9
Demo 4 Mixtures

• Each person will measure 10 mL of distilled water
  using a graduated cylinder and put it in a
  separate cup.
• Volunteer 1 will then measure in 1 tsp of table
  salt and mix with a stirring rod.
• Volunteer 2 will then measure in 2 tsp of table
  salt and mix with a stirring rod.
• Volunteer 3 will then measure in 3 tsp of table
  salt and mix with a stirring rod.
• Volunteer 4 will then measure in 4 tsp of table
  salt and mix with a stirring rod.

10
Observations...

• What are the differences you observe between each
  of our mixtures?
• Did the salt fully dissolve in each sample, or is
  there still solid salt in any sample?
• Which mixtures are homogeneous and which are
  heterogeneous based on your visual observations?
• Properties of each solution need 4 new
  volunteers...

11
Demo Part 2 Measuring Conductivity

• Each person will use a 1.5 V battery and a
  multimeter to measure the conductivity of their
  solution (I will show how to connect the
  circuit).
• What do you observe about each sample? Which
  sample conducts the most electricity (highest
  number)?
• What is the relationship between salt
  concentration (amount per mL of water) and
  conductivity?