Surface Tension Experiments
http://www.hometrainingtools.com/experiments-with-water-science-project/a/1272/
Surface tension is one of water's most important
properties. It is the reason that water collects in drops, but it is also why
water can travel up a plant stem, or get to your cells through the smallest
blood vessels. You can experiment with surface tension using just a few
household items.
What To Do:
1. Start with a cup of water and some paperclips.
Do you think a paperclip will float in the water? Drop one in the cup to find
out. Since the paperclip is denser than the water, it will sink to the bottom
of the cup.
2. Now find out if you can use surface tension to
float the paperclip. Instead of dropping the paperclip into the cup, gently lay
it flat on the surface of the water. (This is tricky - ” it may help to place a piece of paper
towel slightly bigger than the paperclip in the water. Then lay the paperclip
on top of it. In a minute or so, the paper towel will sink, leaving the
paperclip floating on top of the water.) Even though the paperclip is still
denser than the water, the strong attraction between the water molecules on the
surface surface forms a type of "skin" that supports the clip.
3. Now put a drop of dish soap in the water. This
will bind with the water molecules, interfering with the surface tension. The
paper clip will sink. You can try floating other things on top of the water
also - pepper floats well
until you add dish soap. Can you find any other light items that will float?
- There are some insects, called water skimmers (or water striders), which are able to walk on water, by using surface tension. They land on the surface of the water, but are so light they don't break the surface tension. Then by flapping their wings, they can zip around on the surface.
Let's start with the drop of water on the wax paper:
It is easy to see that the drop seems to have a "skin" holding
it into a sort of flattened sphere. It turns out that this surface
tension is the result of the tendency of water molecules to attract
one another (called cohesion). Though teachers often talk about surface tension being like a "skin", this is not really an accurate model...The surface does not react to being poked with a stick as a skin would. In fact, the water not only sticks to itself, it sticks to the wood ...This is called adhesion because of attraction to different substance
- Surface tension can be shown with many other demonstrations, including one in which you add coins to a full glass of water and note how the surface rises well above the rim of the glass.
- Place a small puddle of distilled water -- about 1.5 cm in diameter -- onto a clean acetate sheet. Note the shape of the puddle. Touch the tip of a clean toothpick to a small amount of liquid detergent, and wipe clean. Carefully touch the tip of the toothpick to the surface of the puddled water. Note and record the result.
- Place distilled water in one well of a 24-well plate. Place an equal volume of 1% detergent solution in an adjacent well. Dilute food coloring may be added to each well; this is optional. Place an open-ended glass capillary tube in each well. Slowly remove the capillary tube. Note the length of liquid in each tube.
- Place several drops of milk on a small 2.5-cm watch glass. Add a small drop of food coloring on the surface at a point near the edge of the tiny puddle of milk. Using a plastic transfer pipet, add one drop of liquid detergent on the top edge of the watch glass on the side opposite the location of the food coloring. Note and record the observations. (Alternatively - see "Milk in Motion" post)
1. Kitchen detergents
make water wetter. Explain this statement.
Detergents lower the surface tension of water. Each of the phenomena
studied here has an explanation rooted partially or entirely in the lowering of
the surface tension of water by the detergent. The dye spreading over the milk
is the most complex of the phenomena. Close visual examination shows that the
liquid detergent flows down the glass surface for many, many minutes. As a
result, the detergent concentration at the surface of the milk changes
throughout the duration of the observation.
Q1. Kitchen detergents make water wetter. Explain this statement.
A1. Water with added detergent covers more surface on flat surfaces.
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