Transcript Water Unit

Review of Activities 35-40
Mystery Liquids – Activity #35
 We explored the fact that substances in a liquid phase have
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characteristic properties, just as solids do.
We tried to identify two different liquids. One was water
and one was ethanol (an alcohol).
We investigated qualitative properties such as appearance,
odor, feel on the skin, cohesiveness, phase and tendency to
evaporate at room temperature.
We also measured quantitative properties such as melting
and boiling points, and density.
We should have learned that water has some unusual
properties and that most measurement scales tend to be
defined relative to water.
Vocabulary words learned
 Particle – small pieces or parts
 Phase – the three forms that a substance can be in –
solid, liquid, or gas
 Physical change – distance b/w particles changing
 Vapor - water in the gas phase
Objectives to Activity 35
 Substances have characteristic properties, such as
density, melting point, and boiling point, that are
independent of the amount of the sample.
 Substances generally exist in one or more of three
phases: solid, liquid and gas.
 Phase changes, such as melting and boiling, are
physical changes.
 Scientists set the standards of density and the Celsius
temperature scale based on water’s melting and
boiling points.
Notes to remember
 When we froze water in the freezer, it turned to ice.
 When we froze ethanol, it never froze in our freezer.
 Remember that the lower the temperature, the less
amount of energy so the particles vibrate but they stay
in place.
 Higher temperature means more energy so the particles
move faster to fill the container.
 The basic particles do not change – only the
arrangement and distance between the particles change
during a phase change.
Main ideas
 Substances can be identified based on their properties.
 Liquid A was water based on its properties.
 Lack of color
 Lack of odor
 Round drop
 Density was 0.98 – 1.02 g/mL
 Boiling point was 97 – 103 degrees Celsius (higher than alcohol)
 Melting point
 Liquid B was ethanol based on its properties
 Had an odor
 Did not form a drop on the wax paper
 Boiling point was 75 – 81 degrees Celsius (lower than water)
 Density was 0.75 - 0.86 g/mL
One plus one does not always equal two…….
Space between molecules
Activity #36 – Making Molecules
 We created models of basic compounds such as
 Water
 Methanol
 Ethanol
 We created models of molecules of diatomic elements
such as
 Hydrogen
 Oxygen
 Nitrogen
Can you identify the molecule?
Ethanol
Methanol
Vocabulary terms
 Element – a basic substance that can’t be simplified
 Atom – smallest particle of an element
 Molecule – 2 or more atoms held together with a
covalent bond
 Compound – two or more elements chemically
bonded – a molecule that contains more than one
element
 A is for Atom
Further Review
 We worked with four different elements: carbon, hydrogen,
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oxygen and nitrogen
The ‘sticks’ in our models represented ‘bonds’ with another
atom.
In the molecular formula H2O – what doe the 2 stand for?
The number 2 represents the number of hydrogen atoms in
the molecule.
Remember that elements are a substance composed of only
one type of atom whereas a compound is any substance
made up of two or more elements chemically bonded
together.
Water and alcohols are similar in that they all include
hydrogen and oxygen in OH groups. However, alcohols
have carbon and water does not. Alcohol molecules are
larger.
Activity 37 “What Dissolves?”
 We investigated the solubility of four solids in water.
 Sodium chloride
 Copper chloride
 Cornstarch
 Iron chloride
 We further explored solutions and solubility.
 Key vocabulary
 Dissolve – sugar mixing into water – sugar dissolves
 Solute – the sugar – what YOU are putting in
 Solvent – the water – universal solvent is water
 Solution – the mixture that results of you putting two things
together
Questions
 Must a mixture be clear to be a solution?
 Yes, a mixture must be clear to be a solution.
If it isn’t clear, there are still large particles
in the mixture.
 Must a mixture be colorless to be solution?
 No. Even when the copper chloride
completely mixed into the water and no
particles remained, the solution was blue. If
it is clear, it is a solution, even if it has color.
Activity #38 – Dissolving Duel
 We compared water and ethanol as solvents.
 We performed a controlled experiment that tested for
the relative solubilities of eight solutes.
 Water can dissolve many different solutes and is often
called the universal solvent.
 Water’s ability to dissolve many substances is both
helpful and harmful to living organisms.
 Industrial activity can introduce undesirable
substances into the environment.
Concept Map
Dissolves in
Solvent
Solute
dissolves
Can be
More soluble
form
Solution
More solute
dissolves before
May be
Saturated
Less soluble
Less solute
dissolves before
Questions
 In a solution of sugar and water: Which is the solute?
Which is the solvent?
 Which one is a solution?
 Coffee with cream
 Hot tea
 Soda
 Black coffee
 Muddy water
 milk
Black coffee, tea and soda are solutions because they are clear
Milk, muddy water and coffee with cream are not solutions because
they are not clear.
https://www.youtube.com/watch?v=e-2EoyDYamg
Objectives
 A solution exists when one substance, the solute,
dissolves in another, the solvent.
 Solubility, the amount of a substance that can dissolve
in a particular solvent such as water, varies from
substance to substance.
 Dissolved particles may be detected by sight as a color
change of the solution; un-dissolved particles are
always visible.
 A filter can remove only un-dissolved solid particles
from a mixture.
Questions continued
 What could be done to a sugar solution to make
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it more dilute?
Adding more water to a sugar solution would make
it more dilute
What could be done to a sugar solution to make it
more saturated?
Adding more sugar or evaporating some of the
water
The longer you leave a tea bag in hot water, the
darker the tea becomes. Explain why this happens
in terms of dissolving and concentration?
Dark tea is more concentrated than light colored
tea made from the same tea leaves. The deeper the
color, the more tea is dissolved in the solution.
Activity 39 Contaminants
 We did an activity which followed a water molecule in
a droplet of water through the water cycle – very
similar to what we did in the weather unit however, the
piece that was added was the contaminants. Started as
fairly pure precipitation.
 Water circulates through the earth’s crust, oceans, and
atmosphere in the water cycle. It evaporates from the
surface, rises, cools at higher elevations, condenses as
rain or snow, and falls to the surface where it collects in
lakes, oceans, soil, and rock layers underground.
Water Cycle
 https://www.youtube.com/watch?v=QIst2_0r4Gg
Pass out Transparency 39.1
 Use this as a reference – tape it into Activity #39
 Notice that the solid arrows represent water which has
picked up contaminants
 Notice that the black outlined arrows represent water
as either vapor or no significant contaminants
Activity #40 Parts Per Million
 We were introduced to the concept of serial dilution.
 We can quantify relative concentration of solutions in
parts per million.
 Dilution reduces the amount of solute relative to the
amount of solution but without eliminating the
existence of solute, even when it becomes
imperceptible to the naked eye
 Mathematical relationships are involved in serial
dilution and the expression of concentration of a
solution.
Parts per million
 1 second in 12 days
 1 penny out of $10,000
 1 grain of salt in 2 pounds of potato chips
 1 inch in 16 miles
 1 postage stamp in an area the size of a basketball court
 https://www.youtube.com/watch?v=0Hwqv5sW6sw