Download Activity 3

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
•
•
•
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formed a round drop
held together
could be moved around as a single drop
Liquid B formed a flatter drop
•
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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?
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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.
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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
states of
matter,
cohesiveness
is a property
of liquids
Quantitative
properties,
color is
qualitative
All qualitative
properties,
temperature is a
measurement
All properties
of the
unknown
samples,
comparison is
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?
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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.
•
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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?
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•
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Water and alcohols both include hydrogen
and oxygen in OH groups
Alcohols have carbon and water does not
Alcohols are larger molecules
Name__________
Activity 32, #3
Date_____ Period___
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