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a.k.a.
“EGG”xperiments with Vinegar or How to Grow
Your Own Crystals
In this activity, students
will observe chemical reactions and grow
calcium acetate
crystals.
Students will dissolve eggshells in vinegar, let the liquid evaporate
and witness the formation of crystals. These crystals will look
botryoidal (bumpy – like a bunch of grapes or popcorn).
MATERIALS
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Pickling Vinegar (also known as Extra Strength 7 % acetic
acid by volume) works best but may only be available seasonally
(Fall) in certain grocery stores. Pure White Vinegar (5% acetic acid
by volume) works as well but more volume needs to be used and less
material may end up being dissolved. You need about 250 mL of
vinegar, though more or less may be used depending on the quantity
of solid material you are trying to dissolve.
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Eggshells – crushed, the smaller the pieces the faster the
process, 3 or 4. (If eggshells not available, then use small bits of
gravel, limestone pebbles, chalk, marble chips or calcite. See
Extension Activities below.)
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Container – 500 mL plastic tubs (yogurt, margarine, clear food
containers) Clear containers make observation easier. Lids not
needed unless transportation home is required.
PROCEDURE
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Pour 250 mL
pickling vinegar into plastic tub (500 mL)
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Crush eggshells
and add to liquid.
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Observe immediate reaction for 5 minutes
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Pickling
vinegar will create immediate bubbles (carbon dioxide) and the
smaller pieces will be floated up to the surface on the gas
bubbles.
-
Regular
vinegar will not have as much of a pronounce effect but careful
observation over a few days will show that there is less visible
eggshell materials – namely it is dissolving.
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Place container in a warm spot where it can be
undisturbed & observe changes every few days.
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Evaporation &
deposition will occur.
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Botryoidal
crystal shapes will form on the sides of the tub. Looks like
popcorn.
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Observe until
there is no more liquid left in the container (about 3 weeks).
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This experiment
can be a class demonstration, group activity or a home assignment.
The set up is minimal, the cost negligible, the materials are easy
to obtain and are safe to handle.
-
The initial part
of the experiment takes about 30 minutes which includes teaching
concepts and describing scientific procedures. It takes about 3
weeks for the liquid to evaporate & the crystals to grow. The rate
depends on how warm it is.
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Students can be
assigned to keep a journal & to draw diagrams or take digital
photographs documenting the change. Measuring activities can also be
included (Measure weight of initial liquid & solid and compare to
weight of what is left when only a solid remains).
OJECTIVES:
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Discover that
although rocks are solid, liquids can dissolve them.
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Observe &
understand the concept of chemical change.
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Observe how
calcium carbonate (in eggshells) reacts with acetic acid (vinegar)
to release carbon dioxide (bubbles of gas).
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Observe the rate
of evaporation of the liquid and the formation of calcium acetate
crystals.
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Understand the
terms: acid, dissolve, , carbon dioxide, acid rain, scientific
method, variable, surface erosion, evaporate, liquid, solid, gas,
deposit, crystals, botryoidal, calcium, calcite
Content Applications:
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Water that is acidic (rain, fog & snow or ground
water) can dissolve rocks that are exposed. This is called
SURFACE EROSION.
ACID RAIN
is a commonly heard term.
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Urban
environment: Statues made of marble, buildings built of
limestone
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Natural
environment – Pitted rocks that are exposed, the on-going rock
cycle where ground water carries soluble minerals to other
areas, the creation of sedimentary rocks through deposition and
evaporation.
Scientific Skills:
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Observation skills, predicting, concluding,
journaling
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The process can be used to demonstrate the
SCIENTIFIC METHOD
of experiments and VARIABLES
can easily be introduced after the first run through.
EXTENSION ACTIVITIES
– Challenge your students to change the
VARIABLES of their experiments.
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CHANGE the look of the crystals by adding extra ingredients.
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A rock at the
bottom of the container acts as a place for some of the crystals
to grow on. Most crystals will grow on side of container in a
ring as the liquid evaporates.
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Adding
colored chalk bits will make the liquid cloudy & somewhat color
the resultant crystals.
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CHANGE which acidic liquid is used to dissolve the material.
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Liquids with
low pH have high acidity. Vinegar is listed as having a pH of
2.4 – 3.4. Test a variety of household liquids that are
acidic like: orange juice (2.8 – 4), lemon & lime juice (1.8 –
2.4), grapefruit juice (2.9 – 3.4), pineapple juice (3.3 – 4.1),
cider (2.9 – 3.3), Pepsi/Coke (2.7). Be aware that these liquids
have other active ingredients that might color the resultant
crystals & that additional “sludge” which is organic in nature
will attract fruit flies.
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CHANGE the material which you are dissolving.
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Rocks &
minerals containing calcium: marble (use broken tiles available
from flooring stores), limestone (crushed gravel found in
playgrounds, driveways), calcite, apatite, chalk
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Naturally
occurring items: bones, teeth (baby teeth students have “lost”),
seashells
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Use unknown
rock “crumbs” to test if they are soluble in acid. Good use of
small rocks & minerals that accumulate in the bottom of rock
containers.
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CHANGE the size of the material you are dissolving
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If you crush
whatever you are dissolving, there will be more surface area
therefore the reaction will be faster.
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CHANGE the temperature of the liquid you are using.
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If you
increase the temperature of the liquid, it could speed up the
rate that the material is dissolved and speed up the rate at
which the liquid is evaporated.
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CHANGE the amount of liquid and or the amount of the solid material.
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With less
liquid, less acid is present and therefore less material will be
able to be dissolved and fewer crystals will grow.
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With more
material, more crystals will form although there can be too much
material for the amount of acid to dissolve.
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