Lesson 1
Students begin lesson with a ‘Do Now’ in which they complete
a series of problems (see assessment) that are meant to assess
their knowledge of fractions, equivalent fractions, and the
application of fractions to real world situations.
Students record the Purpose of the lab in their notebooks:
To determine how food-coloring affects the color of water.
Teacher displays eight different beakers, each filled with
200 ml of water. Teacher models how to drop a drop of food
coloring into a beaker of water. Students are instructed to
drop one drop of food coloring into the first beaker, then
two drops into the second beaker, three drops into the third,
four into the forth, ten into the fifth, 15 into the sixth,
20 into the seventh beaker, and 25 into the eighth beaker.
Teacher models how to write procedures in a notebook using
the lab template, (see assessment or student work). Students
write the procedure in their notebooks. Teacher models how
to write an observation. Students write observations in their
notebooks. Teacher asks students for observations and records
students’ comments on chart paper. (Teacher probes for responses
along the lines of ‘the water turns darker as more food coloring
is added,’ etc…). Teacher asks students for explanations for
why the water turns ‘darker’ as more food coloring is added.
Teacher asks students to predict what the term ‘concentration’
means, students record answer in the ‘Questions’ section of
the template. Teacher asks for predictions from class, and
then teacher defines the term ‘concentration’ as the ‘amount
of a substance present in a second substance per some standard
amount of that second substance.’ Teacher breaks down definition
explaining the parts (solute, solvent, and solution). Teacher
asks, “Which of the beakers would have the greatest concentration?
How can you tell?” Students write their answers in the ‘questions’
section of the notebook. Teacher asks for student responses
and probes for responses like, “the color changes.” Teacher
emphasizes that we can observe how the concentration of food-coloring
affects the water, specifically that the water turns a darker
red color as the concentration increases.
Lesson 2
Students record the Purpose of the lab in their notebooks:
To determine how the concentration of sugar affects the taste
of water. Students are given six plastic cups. Students fill
the cups with 100 ml of water. Teacher models how to measure
sugar on an electronic balance. Students measure out different
amounts of sugar to fill each cup according to the chart below.
| Beaker |
Sugar (g) |
| 1 |
0.1 |
| 2 |
0.5 |
| 3 |
1 |
| 4 |
2 |
| 5 |
5 |
| 6 |
10 |
Students write the procedure in their notebooks. Students
record the chart in the ‘Data and Measurement’ section. Students
write fractions to describe the concentration of sugar in
each glass. Students then taste each cup and record their
observations. Teacher then records student observations on
chart paper. Teacher asks,”Which of the cups has the greatest
concentration? Even though we can’t see a difference, how
can you tell which cup has the greatest concentration? Which
cup has the lowest concentration of sugar, how can you tell?”
Students record their answers in their notebooks in the ‘Questions’
section of their notebooks. Teacher asks for students’ responses
and probes for answers like, “We can taste the difference.”
Teacher stresses that we can still observe the difference
between the concentrations even if we can’t actually see the
difference.
Teacher says, “Now that you have learned a thing or two about
concentration, let’s take this a step further.” Teacher asks
students to contemplate a few questions. “What if I take 10
ml of the water from the 100 ml of the sixth beaker, how many
grams of sugar should be in that beaker?” Teacher removes
10 ml from the beaker. Students are given a few minutes to
come up with an answer. Teacher probes for correct answer.
“How did you get the answer?” Teacher probes for an answer
before using equivalent fractions. “We can use fractions to
figure this problem out.” Teacher sets up a fraction to demonstrate
how to relate 10g to 100ml stressing key words like ‘per’
or ‘for every.’
“On the left side of this equation is the concentration of
beaker 6, and the concentration must be equal to the water
I drew out of the beaker. So, now I have to figure out how
many grams are in the water. I realize these two fractions
are equivalent.” Teacher models how to solve for x by multiplying
by the greatest common factor (multiplying the numerator and
the denominator of the right-hand fraction by ten).
Differentiated Lesson: Similar problems can be solved also
using proportional reasoning strategies, specifically the
classic ‘cross multiply and divide method.’ Using this approach
to solve for the variable would be appropriate for grades
7-8.
Teacher gives students two similar problems to work on their
own in the questions portion of their notebooks.
1. If you take 50 ml from beaker 6, how many grams of sugar
would you have taken out? Set up two equivalent fractions
to find the answer.
2. If you take 20 ml from beaker 5, how grams of sugar would
you have taken out? Set up two equivalent fractions to find
the answer.
Challenge Problem: You want a beaker to have a concentration
of 1g of sugar per 10 ml of water. If you need 200 ml of water
in the beaker, how much sugar would you need?
Students present answers on board to the class.
Lesson 3
Teacher discusses how, in a fish tank, there are many concentrations
that need to be carefully monitored. However, we can’t see
or taste many of the substances. But, that doesn’t mean we
can’t still find out what the concentration is. In fish tanks,
one thing that needs to be measured is the amount of dissolved
oxygen. (Students learn about the importance of dissolved
oxygen from websites in later or previous lessons). This can
be measured using an electronic probe. Teacher models the
probe, how it works, and how to use the computer software
to find the concentration of dissolved oxygen in different
solutions. Teacher takes readings from beakers of water that
are different temperatures to model how to use the software
and how to record data and measurements. Students write the
lab procedure in their notes and use the probe to find the
concentration of dissolved oxygen in three beakers of water
at varying temperatures to check against the teacher’s model.
Students record data in their notebooks. Students are then
instructed to find the concentration of dissolved oxygen in
two of the fish tanks. Students record data in their notebooks
along with the data from two other groups.
When students finish, they respond to the following questions
in the questions section of their notebooks:
1. How did you determine what the concentration of dissolved
oxygen was in the fish tanks when you can’t even see, taste,
or touch dissolved oxygen?
2. In what ways are the methods you used to determine the
concentration of dissolved oxygen similar to the methods you
used to determine the concentration of sugar in water or food-coloring
in water? In what ways are your methods different?
3. If there are 3.79 L in 1 gallon, how many milligrams of
dissolved oxygen would be in one gallon of water? Use the
equivalent factions below to figure out the problem.
4. Use the results from last week to figure out how many milligrams
of dissolved oxygen are in the fish tank.
Challenge Problem: A two-liter bottle of coca-cola has a dissolved
oxygen concentration of 0.75 mg per 100 ml. How many milligrams
of dissolved oxygen are in a two-liter bottle of coca-cola?
Students share answers on the board.
