M O T I O N Mixing, separating and liquid

Mixing, separating and liquid
M O T I O N
Why
do two
layers form?
Why
does the dye
colour the water
but not the
oil?
Why
does the oil
rise and
fall?
MAKE YOUR OWN LAVA LAMP FROM SALAD DRESSING!
Water and oil do not mix. Water is more dense than oil so it sinks to the bottom while the oil floats on top. These
lava lamps are made from oil, water and salt.
OBJECTIVES
To understand the similarities and
differences in various everyday materials.
To discuss the ideas of density, mixing
happening? what is changing? and how is it
standing at them to transfer their vote by
changing?
moving.
GENERATING QUESTIONS
ENQUIRY
Give the children a few minutes quiet
Manage turn taking by asking children to
and floating and sinking.
thinking time to reflect fully on what they have
raise their hand if they want to talk.
STARTER
just observed and to create an individual
REFLECTING ON THE ENQUIRY
Play “stand to attention”. Arrange the
class so that the children are sitting in a circle.
Explain to the children that everyone in this
game must stand up, however they must
stand up individually and not at the same time
as anyone else. They must work together as a
group to complete the task but they must not
verbally communicate with anyone: they must
question based on the stimulus. Now split the
class into groups of 3 and ask each member
within the small group to share their question.
Then together in their groups they must
decide on one question they would like to
discuss and record it on an A4 sheet of paper.
SELECTING QUESTION FOR DISCUSSION
Gather in all the questions recorded on
observe others body language and try to
the A4 paper and read them aloud. Place the
guess when they are going to stand up. If two
questions around the room and ask the
or more children stand up together the group
children to vote for which one they would
must start from the beginning again.
most like to discuss by standing next to the
STIMULUS
appropriate A4 sheet. The question with the
Making mini lava lamps (see page 2).
encourage children to describe what they see
with questions like what do you see?, what is
Resource for Teachers
Complete the “Evaluating with
emoticons” activity - see page 3.
most votes will be the topic for the enquiry.
Should a tie situation arise, remove the
questions with fewest votes and ask anyone
1
Wa t e r a n d o i l d o n o t m i x
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M I N I LAVA LAMPS
To do this demonstration you will need cooking oil, food colouring, tap
water, a tall glass or jar and either salt or vinegar and baking powder, or
an effervescent tablet.
Do either variation A or B or C. Ask the children to observe closely at each
stage of the demonstration. Encourage them to describe what they are seeing in
words and in pictures.
VARIATION A
VARIATION B
Pour oil into a tall glass until it is about
Pour oil into a tall glass or bottle until it
a quarter full. Slowly add water until the
is half full. Add water until it is three quarters
glass is about three quarters full. Add drops
full. Add about 10 drops of food colouring
of food colouring and watch them sink
(choose a colour that is easily seen e.g. red)
through the oil into the water (if this
and watch them sink through the oil into the
happens too slowly, stir the oil and water).
water (stirring if this takes too long). When
When there is a good colour contrast
there is a good contrast between the oil and
between the oil and coloured water, pour
water, drop an effervescent tablet into the
some salt onto the oil (about the size of half
oil.
a peanut at a time).
VARIATION C
Pour oil into a tall glass or bottle until it is half full. Dilute some vinegar so that it is about
one part vinegar to 10 parts water. Add this dilute vinegar to the oil until the jar is three
quarters full. Drop some baking powder into the oil - just enough so that it sinks slowly
through the oil (about the size of half a peanut). Observe!
What
happens to the
oil/water/dye/
salt/tablet?
Children can make their
own mini lava lamps, investigating the
science of colour, mixing, floating and
sinking, chemical reactions (version B)
and dissolving.
Following the enquiry, the
demonstration can be recorded and
children asked to write a script to
explain an aspect of the science. This
What changes?
can be used as a formal assessment.
Resource for Teachers
2
For next
time...
try adding a
coloured ice cube to
the glass of oil and
water. Watch as
it melts.
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evaluating with Emoticons
Images © Microsoft Clip Art
Cut out and laminate the emoticons below and place them face-up on the floor (you may need multiple copies). Ask students to reflect on how
they felt during the enquiry, and why, and ask them to select the emoticon that best represents their feelings. Discuss as a class a) what was
positive about the enquiry and b) how the group could improve their enquiry skills. You may want to provide blank laminated paper and a
marker for students who cannot find an appropriate emoticon.
Resource for Teachers
3
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FLOATING
AND
SINKING
L AVA L A M P S
MIXING
Water and oil hate each other and don’t mix (no matter how hard you shake them!)
The oil is always on top because it is less dense than water.
When you add the food colouring, it sinks through the oil because it weighs more than
an equal volume of oil (it is denser). The food colouring likes to be with water (they
are both polar liquids; oil is non-polar) so only the water is coloured.
Oil
The food colouring diffuses (spreads out) when it reaches the water. This is because
the particles that make up the water and food colouring are in constant random
motion.
VERSION A
Salt is more dense than oil so when you pour it in, it sinks - but it brings some oil with
it. When the salt reaches the water, it begins to dissolve and lets the less dense oil
float back to the surface. This accounts for the bubbles of oil you see travelling
through the coloured water.
Water
Only a limited amount of salt can dissolve in water. After the addition of a lot of salt,
the water becomes saturated: no more will dissolve. The salt begins to build up at the
bottom of the jar.
VERSION B
The effervescent (fizzy) tablet contains an acid and a carbonate in solid form. When
they are solid they don’t react, but when they dissolve in water they react to release
carbon dioxide. Carbon dioxide is a gas, and when it is released in water it forms
bubbles.
The bubbles float in both water and oil. As oil and water do not mix the bubbles rise
to the top of the glass where they pop and the remaining water sinks back down to
the bottom of the glass.
Oil and water do not mix:
they are immiscible. This is
because water is polar and
oil is not. Oil floats on
water because it is less
dense than water. Food
colouring is polar like
water. It sinks through the
oil without mixing until it
reaches the water.
VERSION C
The baking powder sinks through the oil into the vinegar. When it reaches the vinegar,
it starts to react, producing bubbles of carbon dioxide gas. These rise through the
vinegar and oil to the air, where they burst.
REAL LAVA LAMPS
In a real lava lamp, wax is held in oil. Cold wax is less dense than oil so it sinks. Hot
wax is less dense than oil so it floats. Cold wax is heated by the bulb at the bottom,
reducing its density. This makes it float in the oil. As it rises, it cools, making it more
dense than oil, so it sinks again.
Foo
sinks d colouri
ng
thro
into
the w ugh the
diffu ater, wh oil
ses (
ere i
throu spreads) t
gh t
wate he
r.
Resource for Teachers
4
Oil containing
Carbon
Dioxide
Effervescent
Tablet
Carbon
Dioxide
Bubbles
In version B, the tablet
releases carbon dioxide gas.
The gas forms bubbles
which rise through the
water and oil.
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