Activity 35: Mystery Liquids by yGb0sMHP

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									                 Activity 35 Analysis
1. Did in class
2. In this activity you compared two liquids.
   a. What properties and measurements were the most
       helpful in identifying the two liquids?
   b. Explain your answer
   • density and boiling point were the most helpful (they
       were most exact)
   • all properties observed and measured could be used
       to tell the substances apart except general appearance
   • All the alcohols had similar qualitative and quantitative
       properties (it could be ethanol or isopropyl alcohol)
3. A liquid forms rounded droplets because
   of its degree of cohesiveness.
  a. Which of the two liquids was more cohesive?
  b. Explain the observations that support your
     answer.
  • Liquid A was more cohesive
      •     formed a round drop
      •     held together
      •     could be moved around as a single drop
  •       Liquid B formed a flatter drop
      •     didn’t stay round or hold together
      •     smeared out over the plastic
4. Why should you keep liquid samples capped or
   covered while studying them?
  •   they can spill
  •   they might evaporate
  •   can spread fumes
5. Which do you predict would evaporate more
   quickly at room temperature: methanol or
   acetone? (Refer to the data in Table 1.)
   Explain why.
  •   acetone
  •   lower boiling point
  •   it would evaporate faster at a lower temperature
  •   observed this with water and ethanol
6. Follow steps a, b, c, and d.
a. Look for a relationship among the words in List 1. Cross out the word or phase
that does not belong.
b. In List 1 circle the word or phrase that includes the other three.
c. Explain how the word or phrase you circled is related to the others.
d. Repeat steps a–c for each of the remaining lists.

List 1             List 2                    List 3                     List 4

Liquid             Density                   Odor                       Property

Solid              Boiling Point             Feel                       Cohesive

Gas                Quantitative Property     Color                      Liquid

Cohesive           Color                     Temperature                Comparison

States of Matter   Melting Point             Qualitative Property       Clear

Common             Quantitative             All qualitative            All properties
states of          properties,              properties,                of the
matter,            color is                 temperature is a           unknown
cohesiveness       qualitative              measurement                samples,
is a property                                                          comparison is
of liquids                                                             not a property
Follow-up
Part B
            Activity 36 Analysis
4. What does the 2 in the molecular formula H2O
   stand for? Explain.
  •   Number of hydrogen atoms in the molecule
5. In this activity, you modeled ethanol, hydrogen,
   methanol, nitrogen, oxygen, and water. Why are
   oxygen gas, hydrogen gas, nitrogen gas, and
   carbon called elements, while water and
   ethanol are called compounds?
  •   An Element is composed of only one type of atom like
      carbon, hydrogen, nitrogen, and oxygen
  •   A compound is composed of two or more different
      atoms chemically bonded together. Water and
      ethanol both have two or more different elements
      (atoms) bonded together
6. Methanol and ethanol are both alcohols.
  a. Compare: How are the molecules of methanol
     and ethanol similar?
  • Both are made of the same three elements
     and both contain an OH and a CH3
  b. Contrast: How are the molecules of methanol
     and ethanol different?
  • Methanol contains one carbon atom
  • Ethanol contains two carbon atoms
  • Ethanol has more of a chain structure since it
     has more carbons
7. a. Why is the formula for methanol usually written
      as CH3OH instead of CH4O?
  •     The formula CH3OH better describes the structure of
        the methanol molecule
  •     From the formula CH4O, you can’t tell how the oxygen
        atom is involved in bonding without building a model
  b. Looking at its structure, propose two ways other
     than C2H5OH to write the formula for ethanol.
     Describe the advantages and disadvantages of
     each.
  •     C2H6O,gives correct # of each kind of atom, but doesn’t
        show structure
  •     CH3CH2OH is long, but it most clearly suggests the
        structure of the molecule
                                                Liquid at
                                                room
                                                temperature


                                                Gas at room
                                                temperature




• This is called a molecular isomer
• They have the same number and type of atoms, but
  they are arranged differently
• Molecular size and structure have many effects on the
  physical properties of a substance
   – Density
   – Melting point
   – Boiling point
8. Compare and contrast water with the two
   alcohols you modeled. How are they the
   same? How are they different?
  •   Water and alcohols both include hydrogen
      and oxygen in OH groups
  •   Alcohols have carbon and water does not
  •   Alcohols are larger molecules
Name__________     Date_____ Period___


 Activity 32, #3
                    Activity 37




Title: What Dissolves?
         Water Contamination
• Water is not always pure.
• Dissolved substances can be helpful:
  – Salts dissolved in our blood and in our food and
    drink.
• Substances may be unpleasant to smell or
  taste or are harmful to humans or other
  organisms.
• Water contamination refers to undesirable
  materials dissolved in water.
• You will begin to investigate how things
  dissolve in water.
              Read C-39
Problem: What makes a mixture of a solid
and a liquid a solution?

Hypothesis/Initial Thoughts:
         Sugar Mixed in Water
• As the sugar mixes in:
                  • Dissolving
• When all sugar has disappeared:
                   • Dissolved
• Sugar dissolves in water:
                     • Soluble
• The mixture that results after a solute
  dissolves in a liquid such as water:
                    • Solution
• Flour does not dissolve:
                   • Insoluble
          Solute




Solvent
Procedure:
Follow procedure on pgs. C-40 to C-42
1. Put solid in appropriate cup instead of on
  a paper towel.
Note: In step 5, Using Table 2, make sure
  you put the correct number of scoops in
  the assigned cup listed in the table.

In step 11, demo on how to use filter paper.
           Did it dissolve?
• If the solute (solid) dissolves, the
  solvent (liquid) will be clear.
• If the solution is cloudy and you cannot
  see through it easily, it is not a solution.
  The material is suspended in the liquid,
  it is not dissolved.
Follow-up
Vocabulary sentences:
• Solute
• Solvent
• Solution

Write a sentence to describe your
 observations in the vocabulary section of
 your notebook for the above vocabulary
 words.
               Saturation
• In some cups, the water (solvent)
  dissolved some, but not all of the solid
  (solute)
• When there is solid left over after you have
  stirred and seen some dissolution, it
  means that the solvent can hold no more,
  the solution is saturated.
     In which cups did you see
            saturation?
• Cup 2: sodium chloride
• Cups 7 & 8: iron chloride
• Cornstarch cannot be considered a
  saturated solution since there was no
  evidence that any cornstarch dissolved at
  all
    Variables in this Investigation
• Controlled variable: the variable(s) which is held
  constant
   – The amount of water added to each cup
   – The temperature
• Independent variable: An independent variable is
  the variable you have control over, what you can
  choose and manipulate. It is usually what you
  think will affect the dependent variable.
   – The four solids
   – The two amounts used for each solid
• Dependent variable (or responding variable): It is
  the variable that depends on other factors.
   – Whether or not the solids dissolve to form a solution

								
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